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Factors affecting induced color
Yision Rev.
Vol. 2. pp. 503-525.
Pergamon
FACTORS
Press
1962.
Printed inGreat Britain.
AFFECTING
INDUCED
COLOR
Jo ANN S. KINNEY U.S. Naval Medical Research Laboratory, (Received
Groton, Connecticut
3 August 1962)
Abstract-The amount of color induced into a field of Illuminant A was determined for four inducing colors, red, yellow, green and blue, by having observers compare the induced color with a field of actual colored light. The results, given in C. I. E. values, show that the amount of color induced increases as the size of the inducing field is increased, as the luminance ratio between inducing and induced fields is increased, and, to a small extent, as the purity of the inducing color is increased. R&un~&-La quantite de couleur induite dans un champ de l’etalon colorimetrique A fut mesuree pour quatre couleurs inductrices, rouge, jaune, verte et bleue, en faisant comparer aux observateurs la couleur induite avec un champ de lumitre reellement color&e. Les resultats, don& en valeurs C.I.E., montrent que la quantite de couleur induite augmente avec la dimension du champ inducteur, avec le rapport des luminances entre champs induit et inducteur, et pour une faible part avec la purete de la couleur inductrice. Zusammenfassung-Indem die Beobachter die induzierte Farbe mit einem Feld, das mit einer reinen Farbe erleuchtet war, verglichen, wurde der Anteil der induzierten Farbe in einem Feld der Lichtart A fur vier Farben, nlmlich Rot, Gelb, Griin und Blau gemessen. Die Ergebnisse, die im C.I.E.-System dargestellt sind, zeigen, dass der Anteil der induzierten Farbe in der gleichen Weise ansteigt, wie die Grosse des induzierenden Feldes wlchst, wie der Helligkeitsunterschied zwischen dem induzierenden und dem induzierten Felde zunimmt, und in geringem Masse wie die Reinheit der induzierenden Farbe grosser wird.
A MAJORcontribution by LAND (1959a, b) in his demonstrations of two-color projection has been to restimulate interest in the phenomenon of induced color. Within the last few years, reviews of the subject by WALLS (1960) and by JUDD (1960) and experimental data by SELF (1959), WILSON and BROCKLEBANK (1960), KARP (1959), and JAMESON and HURVICH (1959, 1961) have been reported. Compared with the previous fifty years of inactivity, the change is impressive. On the other hand, little of the recent data is applicable to the formulation of laws stating how much and what kind of color is induced under various conditions. One reason is that many of the investigators were interested in the complex stimulus conditions used by Land. Another is that much of the newer work has utilized the technique of color-naming, a method that does not lend itself readily to quantification. At the end of the nineteenth century, investigators did attempt to find generalities for predicting the variables underlying induced color. The classical laws of KIRscHMANN (1890) stated that the saturation of the induced color increased with increasing size and increasing saturation of inducing color and with decreasing brightness contrast between the two areas. Although these laws are still widely quoted, few attempts have been made to verify them. SELF (1959) investigated the effect of purity and luminance ratio on induced color and found that saturation increased with increasing purity and with increasing luminance of inducing field. JAMESON and HURVICH (1959) also cite examples of increased saturation with increased surround luminance. WALLS (1960) disagrees with Kirschmann’s law 503
concerning purity of inducing color, stating that highly saturated colors are seen when the inducing color is tlooded with dim white light. The particular hue induced under simple stimulus conditions has not received much attention, since it has been known since Fechner to be roughly complementary to the inducing hue and since individual differences in sensitivity and pigmentation easily account
for the variations. Self, using Illuminant C as the induced field, also concludes that the hues are complementary and do not change with the purity or the luminance of the inducing color. The purpose of this investigation, therefore, was to obtain quantitative data on the factors influencing induced color by having observers compare the color induced in a given area with that of a field of actual colored light. The effect of the size, purity and luminance of four inducing colors was studied for an induced field of Illuminant A. APPARATUS
A Bausch & Lomb projection calorimeter was used to provide the stimuli. The colorimeter consists of three separate projecting systems from a single light-source, an inside frosted 300W lamp of 2854°K. The light from each projecting system can be varied in intensity by the setting of diaphragm blades and, in form and spectral composition, by appropriate templates and filters. In addition, filter holders are provided in an out-of-focus position to yield an additive mixture of the light transmitted by two filters. The position of the two filters relative to the path of light can be varied in small steps between the two end positions; the spectral composition of the projected light can thus be varied from that transmitted by one filter to the other with all mixtures in between. A group of approximately thirty Wratten filters, mounted in cover glass, gave comprehensive control of chromaticity values. The spectral transmissions of these filters were measured on a G.E. Spectrophotometer and C.I.E. values calculated for Illuminant A. Luminances of llluminant A on the screen were measured with an ultra-sensitive Spectra Brightness Spot meter. STIMULI
Figure 1 is a representation of the stimulus field. At the top is the field as it appeared when focused on a white Bainbridge board screen; at the bottom are the components of the field. Light from the first projector was filtered so that it provided a circular field of color with a vertical unlighted strip in the center. Light from the second projector was focused on the same area of the screen. Light from the third projector, used in conjunction with the movable filter holders and Wratten filters, provided the comparison field. Three stimulus parameters were investigated. First the size of the vertical unlighted strip was varied. The diagram shows the lo strip; a 2” strip and a r strip were also studied. The field size remained constant at 5”, so as the strip was decreased in size the colored or inducing area varied from 3” to 4$“. Secondly, the purity of the colored light was varied by changing the amount of Illuminant A from the second projector. At one extreme five times as much Illuminant A as colored light was used, resulting in a very desaturated inducing stimulus. At the other extreme, arbitrarily defined as maximum purity, all Illuminant A was removed from the semi-circular fields. This is indicated in the diagram by the dashed lines; under this condition only light from the second projector was in the center strip.
505
Factors Affecting Induced Color
The third parameter was the luminance ratio between the semi-circular fields and the center strip. Not all combinations of all parameters were investigated. In general, two parameters were held constant, while the third was varied. The effect of purity and luminance ratio was studied for the medium, 1” strip ; with purity the variable, the luminance ratio was 1.2/l ; with varying ratios, purity was maximum. The effect of the size of the inducing field was determined for the minimum purity and 1*2/l luminance ratio. When evidence of interactions between parameters was found, other combinations were studied. COMPARISON FIELD
INDUC~ON FIELD
Projector FIG.
1.
I
Projector 3
Projector 2
The stimulus field, as it appeared to the observer, and its components.
Four different inducing colors were investigated. Table 1 gives the chromaticity values of these four colors together with the values for the various purities, or mixtures with Illuminant A, and the maximum luminance used. TABLE
Purity condition
Red #33 Yellow # 16 Green #60+#65A Blue #44A
1. DESCRIPTION
Y
06766 0.5590 0.0843 0.1280
0.2666 0.4386 0.6509 0.3463
COLORS
X
Y
z
X
Y
z
Max. Lumill. used ft-L
0.5860 0.5011 0.3077 0.2748
0.3223 0.4228 0.5012 0.3744
0.0917 0.0761 0.1911 0.3507
0.5012 0.4651 @4072 0.3869
0.3745 0.4124 0.4346 0.3961
0.1243 0.1225 0.1582 0.2170
0,260 O-260 0.094 0.260
Equal amounts Color & Illum. A
Maximum x
OF INDUCING
I 0.0568 O+-rO23 0.2648 0.5257
5 times as much Illurn. A
Luminance levels of the inducing colors varied around 0.1 f&L. Preliminary investigation revealed that the absolute level was not a factor in the amount of color induced as long as the ratio between inducing and induced fields was constant. Nevertheless, the luminances of the red, blue and yellow were kept the same for ease of comparison; the luminances of the green-inducing color were lower, due to the lower transmission of the green filter.
PROCEDURE
The observer viewed the screen binocularly from a seat 10 ft away. Between presentations a shutter blocked the colored light from the first and third projecting systems so that the field consisted of Illuminant A from the second projector viewed against a dim surround of 0.001 ft-L of Illuminant A. The total field was exposed from 2 to 3 set with 10 set between exposures. Data were taken for four observers, all of whom had normal color vision. The color induced in the center strip was compared with the actual colored light in the comparison field, which could be varied in hue, saturation and brightness. The method of constant stimuli was used to determine saturation limens. The comparison field was set at given proportions of color;Illuminant A and the observer was asked, in one series, whether the induced color was more saturated, and, in another series, whether the comparison color was more saturated. He was instructed to glance briefly from one to the other to make his comparisons. Ten judgments at each of five settings of the comparison Before saturation judgments began, the comfield were used in each series of judgments. parison field was varied in brightness and hue until it appeared equal to the induced color in these respects.
96 96
90
\f I \\
E
I
0 50 .z f 40 0 p 30 'i: al y 20 It
1 l
I\ I\
IO
I
2
tll’JJ~\.“‘~’
& Al;
0.05
A
I
SIZE INDUCING
9 I
--
OF FIELD 30
-
40
-___-
4 3/40
0
I \ 4
\
I’ I
a
1.
\
I
\
I
0.15
0.25
0.35 Proportion
0.45 of wrotten
0.55
0.65
# 21
FIG. 2. Sample data showing the effect of (a) the size of the inducing field, and, opposite, (b) the
purity of the inducing color, (c) the luminance ratio between inducing and induced fields.
(a>
507
Factors Affecting Induced Color
96 96
90
$30 E?O S60 -: 50 B E 40 :: a 30 .
---
-017
0 -033 10
0 --0.50 & ---
Maximum
@360
4 2 0.15
0.25
Proportion
0.35
09
0.45
of Wratten
# 21
98 96
E: 80 E F 70 2 60
!
I \ \
!
I
! f
il
5 2
1
r 8 f
All A
0.15
v
II
_____ 0I
- -
I
‘, I
1 \ \
‘:
IIL
-
,
I\
I ,
RATIO
INDUCING TO INDUCED FIELDS
1 \
I\
II
ace
\I
LUMINANCE
I
10
I
I.2 to
to I to I
---4
I
\
,
t
I
\
, 0.25
0.35 Proportion
o-45 of
Wratten
(121
All Filtered
@I
RESULTS Figure 2 shows examples of the individual data given to show the method of obtaining it and the type of saturation differences found. The inducing color is blue, Wratten #44A, for all. The light in the comparison field is a mixture of Wratten #21 (Dominant A=594 m,u) and a neutral filter; the c~omatici~ values of the comparison field thus lie on a line connecting Illuminant A and 594 rnp. Figure 2a shows the data for one observer for the three sizes of inducing field in terms of the percentage of times the comparison and the induced fields were judged to be more saturated. In all of the plots on probabi~ty paper there are pairs of intersecting lines; the
II
508
Jo ANN S. KINNEY
one with the negative sfope of each pair refers to judgments of the induced field; the one with positive slope refers to those of the comparison field. For example, with the 3” field, when the comparison field was set at a mixture of twenty per cent color (Wratten #21), eighty per cent Illuminant A, the induced field was judged to be more saturated ninety per cent of the time, while at a setting of thirty per cent color, seventy per cent llluminant A, the comparison field was more saturated 100 per cent of the time. The proportion of color in the mixture increases as the size of the inducing field increases and the amount of the increase is such that there is no overlap of judgments from one size to the next.
FIG. 3. C.I.E. diagram of the data for the four observers with the green-inducing various luminance ratios.
color at
Figure 2b is a sample of the data for another observer with purity the parameter; the axes are the same. Saturation limens increase with increasing purity, but the effect is small; the judgments overlap each other throughout the entire range from an inducing color very near Illuminant A to one close to the spectrum locus. Figure 2c shows the data for different luminance ratios between inducing and induced fields. The proportion of color needed in the comparison field increases from twenty per cent to eighty-two per cent as the luminance ratio between inducing and induced fields is increased from O-5 to 4.0. The proportion of color to Illuminant A at the midpoint between fifty per cent limens for induction and comparison fields was converted into C.I.E. values for each of the experimental conditions. Fjg. 3 shows an example of the data for the four observers on a C.I.E.
509
Factors Affecting Induced Color
diagram. The inducing color is green at its maximum purity and 4” size; the experimental parameter is the luminance ratio between inducing and induced fields. The data for the four O’s are plotted on four lines, since each 0 used a different Alter, mixed with Illuminant A, in the comparison field. This result is typical of the inter-observer differences found throughout the experiment; that is, the effect of experimental parameters in increasing or decreasing the saturation of the induced color was the same for all O’s, but the hue of the color induced varied consistently with the particular 0. For this reason, the individual data, given in C.I.E. values, are tabulated in the Appendix and the average C.I.E. values for the four O’s are shown in the remaining figures.
MEDWM
SIZE
MAXIMUM PURITY LUM fNANCE RATIO
0.6
X
I to2
0
I.210 I
o-5
Y
0.4
595 600
\
to RED
WHITE
INDUCING \ 67, y=O.267 0
D.4
0.5
06
X FIG. 4. Portion of C.I.E. diagram showing the average data for various luminance ratios of inducing to induced fields for the four inducing colors.
Effect of Luminance Ratio. Figure 4 gives a portion of the C.I.E. diagram on which the average data for the four observers have been plotted to show the effect of the luminance ratio between inducing and induced fields. The other experimental conditions are constant, size at 4”, and purity at its maximum value. In addition, lines are indicated connecting Illuminant A to the four inducing colors, all of which, with the exception of the yellow, lie beyond the limits of this portion of the diagram at maximum purity. When the luminance ratio is l/2; that is, the induced field is twice as bright as the inducing field, all the induced colors lie very close to Ilhuninant A. As the luminance of the inducing field, relative to the induced, is increased, the induced colors move away from Illuminant A in a direction that is roughly opposite to the inducing color. The opposition is only approximate, since if perfect all points would lie on the lines. Relative to the white point
510
Jo
ANN
KINNFY
S.
(x=y-O-33) on the C.I.E. diagram, the change is primarily one of hue, the colors changing from a hue close to that of Illuminant A toward the hue of the complement of the inducing color as the luminance ratio is increased. EfSect of Size. Figure 5 shows a portion of the C.I.E. diagram for the experimental parameter, size of inducing field. The inducing colors, all at the minimum purity condition, or a mixture with five times as much Illuminant A as color, are indicated by the triangles. For each inducing color, the amount of color induced increases as the size of the inducing field is increased. Also, in each case the color induced by the largest field size, 4$“, is farther away from Illuminant A on the diagram than is the inducing color itself. Once again, when compared to an equal energy white point, the hues of the induced colors change toward the complement. -
-
-____-..
555
560 \
SIZE /NDUCfNG
OF F/E/d
Y
x0
\
0.6
0.5
Y #60t65A+
5A
0.4
#-33+
cl.3
0.4
5A
0~6
0.5 X
FIG. 5. Portion of the C.I.E. diagram showing the average data for the various sizes of inducing fields.
The amount of increase in color on the C.I.E. diagram does not relate linearly to the field size since the distances between the values for the 4” and 4F fields are greater than that between the 3” and 4” fields. Efict of Purity. Figure 6 shows the data for different purities of each inducing color. Purities range in each case from a color very close to the spectrum locus to one near Illuminant A. The induced colors, however, show much less variation. The colors induced by the blue and green do show an increase in saturation with increasing purity although the differences are not as great as those shown for the other experimental parameters. The colors induced by red and yellow, on the other hand, show little or no effect of purity.
511
Factors Affecting Induced Color
Inspection of the individual data for red and yellow, given in the Appendix, reveals that differences between purities exist but are not the same for each observer. For some observers, the major shift is one of hue; for othas, the minimum purity condition yields the most color. INDUCJNG COLORS A A
560
565
l
\
INDUCED COLORS X
PURITY 5A+Color A+ Color
0 l
All Color
570
to GREEN
\
575
:EN ,P
to BLUE
(#44A)
\ l
\
apoo \05
WHITE 5
L-
Ll
FIG. 6. Portion of the C.I.E. diagram showing the average data for different purities of inducing colors.
Interactions between Parameters. Since the data for variations of a single parameter with the other two held constant gave clearcut relations, various other combinations of parameters were investigated to determine whether or not the effects were cumulative. A number of combinations are possible, but two were studied in detail, the combination of parameters that, when presented singly, yielded the most color and the least color. Figure 7 shows a C.I.E. diagram of the effects obtained by these two combinations of parameters. The results for a combination of conditions which yielded the maximum amount of color are shown by the crosses. These conditions were the largest-sized inducing field, maximum purity and a 2/l luminance ratio between inducing and induced fields. Also given on the diagram are the inducing colors, specified by their filter numbers, and the complements of the inducing colors, shown by straight lines drawn from the inducing color through an equal energy white point to the spectrum locus. Large amounts of color are induced by these conditions, revealing the effects of single parameters to be cumulative. Furthermore, the induced hues have changed greatly from that of the dominant wavelength of Illu~nant A. Viewed in connection with the specified white, the induced hues for each of the four inducing colors have moved away from the hue of Illuminant A towards that of the complement; under these conditions the movement has been approximately half-way to the complement.
.I() ANN S. KINNEY
511
The use of the term “maximum induced color” refers only to the conditions of this study and does not imply that no further color would be found if the ranges of the experimental parameters were increased. A few increases in range were indeed tried, and Fig. 2c has shown an example of further increase in color with a 4/l luminance ratio. In general, however, extreme conditions were difficult to investigate and were not included. The increased luminance ratio, for example, resulted in such dark colors (see next section) that judgments became difficult.
._ _~__~ I
A
INDUCING COLORS INDUCED COLORS t .
0
0.10
3800.20
0.30
0.40 x
0.50
MAXIMUM MINIMUM
of30
0.70
I
0+30
FIG. 7. C.I.E. diagram showing the chromaticity
values of largest and smallest amounts of color induced under the conditions of this study.
The data for the least color are given in the diagram by the circles. With the minimum purity, smallest field size and smallest luminance ratio, the color induced by the green and the blue could be reduced considerably but could not be eliminated within the ranges used here. However, it was possible to obtain an induced field which was not noticeably different from Illuminant A by using the smallest field size and luminance ratio and the maximum purity for the red- and yellow-inducing colors. The next two examples of this effect are given in terms of the actual data, since the differences are so small that they are difficult to depict on the C.I.E. diagram. Figure 8 shows the percentage of responses for two observers for the yellow-inducing color. The abscissa is the proportion of filters #44A and #16 required for the comparison field to be judged bluer in one direction and yellower in the other than the induced color, (Since little or no color was induced, the usual saturation judgments could not be used.) For comparative
513
Factors Affecting Induced Color
purposes, data were also taken with no inducing field present; this was possible since a given proportion of #16 and ##A is a metamer of Illuminant A. For both observers, the maximum purity of the yellow-inducing hue gives comparable results to that of Illuminant A alone, while the mi~mum purity yielded judgments on the blue side of this match.
I
\
II
6
I
I-- lk i
\
1\ I 1 1.
: : : I :
PURITYOF INDUCING
FJELD
----
MAXIMUM MLWIMUM
-
NO INDUCING FIELD
J +-BLUER
PROPORTION OF FILTERS *44A
-+I6
YELLOWER+
FIG. 8. Comparison of the effect of minimum and maximum purity of the yellow-inducing color under conditions yielding small amounts of induced color.
Table 2 gives comparable data for the smallest size of the red-inducing color. The liminal values show that the minimum purity of the red-inducing color results in an induced hue that is slightly greener than that produced by the m~mum purity. In order to determine whether this reversal with purity was true in general for the redand yellow-inducing hues, other parameters were varied to increase the general level of color induced. This was done for the yellow-inducing color by using the largest-sized field and for the red by increasing the luminance ratio to 2/l. The average C.I.E. values are TABLE
2.
COMPARISON
OF LIMINAL
VALUES*
OF COLOR
INDUCING
Purities of #33 (Red) 5A+ color A + color Al1 color No inducing field
MS 0.322 O-326 0.336 0.336
INDUCED
Observers MC JK o-305 o-303 o-310 0.318
BY VARIOUS
PURITIES OF
3”
RED-
FIELD
O-296 O-307 0.322 0,313
FD
Mean
0.286 @288 O-284 0.320
0.302 o-306 0.313 0.322
* Units are proportion of #33 in mixture of #33 and #60+ indicate all 60+ 6.5A (green) and 1.0, all 33 (red).
#65A in comparison
Mean C.T.E. values X Y o-442 0-W 0448 0.455
o-421 0.420 0.417 0.413
field, Zero would
514
Jo
ANN
S.
KINNEY
given in Fig. 9. Under these conditions the colors induced by yellow and by red do behave comparably to the blue and green; the amount of color induced increases with the purity of the inducing cotor and the hue moves away from that of Illulninant A. For the red the major change is one of hue.1
PURITY l
OF INDUCING 5A+
COLOR
FIELD
j .; -1
0 A + COLOR ___....___
;
/
o.30/&&_---~---+.--
x
_.__./ ~__.__ .‘__
All
COLOR
-----LT_.._.+
FIG. 9. C.I.E. diagram showing the effect of various purities of red- and yellow-inducing colors under conditions yielding large amounts of induced color.
Thus, for the red- and yellow-inducing colors, conditions which result in little induced color reveal the minimum purity to be as effective or more so than the maximum. With conditions yielding large amounts of color, however, the maximum purity condition gains in effectiveness and becomes comparable to that found with the blue and green. This interaction can be seen in the individual data given in the Appendix. At these intermediate color conditions, the purity condjtion which gives the greatest amount of color varies with the individual. Induced Brightness. The colors induced under the various experimental conditions varied in brightness as well as chromaticity, and measures of the luminances at which the comparison field was set in order to appear comparable to the induced field are also available. Figure 10 gives these data for each of the four inducing colors as a function of the 1 The c&or induced by the less pure reds, described as a highly saturated pea green, proved difficult to match, since yellow-green filters of high purity are rare. Filters, or combination of filters which appeared to have the necessary saturation, were not yellow enough, and those with the proper hue were not saturated enough. Au acceptable combination, however, was found for the minimum purity condition by combining a green (#53) and a yellow (#12) filter, the resulting combination lying close to the Y-G spectral locus.
515
Factors Affecting induced Color Actual
Luminance
of
Induced
Field
NO
Induction
I.0 Color
..“----.
Red
O---O
7 f
Inducing
X----
&IO
:\
q
cl -;
$
Blue X
Yellow
-,--n
Green
t-t
White
a
4’ 2
E
0.6
:: .
2
I
s [email protected]
Actual
Luminance
Induced : z 1
Field
of
used
with Green
’ \
0
. . ‘:
‘a._ -0
z
0.065 Luminance
Oe56 of
Inducing
Field
0??6 (Ft.L.)
FIG. 10. The effect of the luminance ratio between inducing and induced fields upon the apparent brightness of the induced field. Measures are in terms of the luminance at which the comparison field was set.
luminance level. Also given are the data for a white field, taken under the same conditions as the colors, for comparative purposes. The graph at the left gives the data at the actual levels used; on the right the data are given in terms of ratios so that the green could be compared with the other colors. In all cases the induced field appeared dimmer than the comparison field since the surround of the former (the inducing field) was always greater than that of the latter (general background-0301 ft-L). As the luminance of the inducing field increases, the comparison field is set at progressively lower values to match the appearance of the induced field. Within the range used here the data are acceptably fitted by a straight line; the same line could be used to fit the blue, green and red, and a different line, with greater slope, the yellow and white. On a log-log plot, Fig. II, the curves fall rapidly as the luminance of the inducing
iNDUClNG
COLOR
.
RED
Q
BLUE
0
GREEN
03-
x
YELLOW
z
+
WMITE
\
+ x
a zel-i
LOGFIG.
LUMINANCE
RATIO
(INDUCING/INDUCED
FIELDS1
11. Apparent brightness data plotted on a log-log scale.
51 0
Jo
Awry S.
KINN~\I
field is increased beyond that of the induced. This drop is indicative of the fact that at higher luminance ratios the appearance of the induced field rapidly approaches black. The approach to black is more rapid for yellow and white than the other colors. The dotted line indicates the connection between the 1.0 ratio on the abscissa to the theoretical match of no brightness induction if the inducing/induced ratio were the same for the induced and comparison fields (OXlO1~0~13or 0*001/0.047).
DISCUSSION
A comparison of the results of this study with the classical laws of KIRSCHMANN(1890) on color contrast reveals agreement that the size of the inducing field is a major variable in the amount of color induced. Further agreement is found on the effect of the purity of the inducing color. Kirschmann stated that induced color increased with saturation although the function was one of diminishing returns. We find, in general, increased induced color with increased purity although the sizes of the differences are very small compared to the differences in inducing purities used. In addition it should be pointed out that it is possible to find induced colors that are more saturated than their inducing colors and to find combinations for which the least pure colors are the most effective. These facts, coupled with the small effect in general, help account for the continuing disagreement found in the literature on this question. Kirschmann’s third law, that greatest color is induced when there is no brightness contrast between inducing and induced fields, has not been upheld. Our results are, however, in agreement with all the newer work in the field; both SELF(1959) and JAMESON and HURVICH (1959) found more color induced with larger luminance ratios between inducing and induced fields. All investigators agree that the least amounts of color are induced when the induced field is the brighter; on the other hand, an upper limit is placed upon the increase of induced color as the luminance of the inducing field is increased, since with ratios of sufficient size the induced color appears black. This complication of induced brightness contrast is discussed below and was probably a factor in Kirschmann’s results. The shift in the hue of the induced color with the various experimental parameters, a result of this study, has not received much attention, since it is not found when a neutral stimulus is used in the induced area. The phenomenon, however, is part of the history of colored shadows and has been discussed by many (EVANS, 1943; KARP, 1959; WALLS, 1960). The direct stimulation of the induced area, in this case Illuminant A. cannot be discounted, and the resulting color appearance must be a mixture of the direct stimulation and the contrast color. In this investigation, using conditions which minimize the effect of the direct stimulation, it has been possible to show a shift in the appearance of Illuminant A approximately half-way toward the true complement of the inducing color. The color appearance of the complement only is probably a theoretical limit not actually attainable in practice. The result is, however, applicable to Land’s beautiful color renditions, since the appearance of the colors shifts dramatically under the various experimental conditions. The hue shift, coupled with brightness differences, yields colors of remarkable diversity. The color names employed to describe those colors induced by the blue, for example, would include canary yellow, antique gold, toast and Indian red. It should be remembered in this connection that no light from the inducing color, but only Illuminant A, was presented in the area under investigation; combinations of two illuminants in the same area open a further expanse of possible colors.
Factors Affecting Induced Color
517
The brightness induction effects found in this study relate closely to work of other investigators. Linear relations between apparent brightness of the test field and the luminance of the inducing field generally have been found with limited luminance ranges (HESS and PRETORI,1894; WOOLWORTH, 1938. More complete investigations over wide ranges have been made by DIAMOND(1953) and by HEINEMANN(1955). Both authors found a curvilinear function between apparent brightness of a test spot and inducing luminance on a log-log plot; for inducing luminances somewhat below the level of the test field the brightness is slightly reduced, while for luminances above the test field the reduction becomes much more rapid. The curves of the two authors differ in the rate of the drop found above the test field luminance. Diamond’s reductions are relatively gradual and show effects for more than two log units. On the other hand, Heinemann’s drop rapidly, and he states : “the effect of inducing fields whose luminance exceeds that of the test field by more than approximately O-1log unit cannot be measured; for inducing fields of greater luminance the test field appears darker than the ~ompa~son field for any suprathreshold luminance of the latter” (HEINEMANN,1955. This difference undoubtedly relates to the stimulus fields used by the investigators; Diamond’s inducing field was square with only one side adjacent to the test field, while that of Heinemann was circular and completely surrounded the test field. The curve found in this study (Fig. 11) is intermediate between Diamond’s and Heinemann’s in the extent of the drop with inducing luminance. With luminances of approximately one log unit or more the induced color appeared black and no measurements were possible. The spatial relations between inducing and induced fields were also intermediate to those of the two authors, since approximately eighty per cent of the induced field was immediately adjacent to the inducing. This analysis points up another variable, not investigated in this study, affecting induced color: the spatial relationship between the inducing and induced fields. JAMESONand HURVICH (1961) have studied this aspect and have shown that the amount of color induced increases with the amount of contiguity between inducing and induced fields. Further changes in the appearance of the induced color would be expected from the varying amounts of brightness-induction that result from different stimulus configurations. These investigations on b~~tness contrast have all been done using white light. To the knowledge of the author, there are no comparable, systematic studies dealing with the brightness-inducing qualities of various colors. The indication in these data that blue, green and red behave comparably in this respect, while yellow gives similar results to those of white, is interesting from the theoretical point of view, and lends support to interpretations, such as that of BOYNT~N (1960), that yellow and white cone functions are similar. A major di~culty in determining functional relations for parameters affecting induced colors is the lack of an adequate system of color-spacing in which to specify the results. Several alternatives are possible. First, one can specify strictly in terms of the operational measures used in matching the induced colors. Kirschmann’s data are given in degrees of color on the color disc; in this investigation such specification would be in the proportion of a colored filter used in comparison mixture. The obvious disadvantage of such a procedure is Jack of generality, since the relations will refer only to the particular colored paper or filters used. A second alternative is to specify the colors in one of the better known color systems; the disadvantage here is that one is restricted by the limitations of the system itself. Self chose
the Munsell system and plots Munsell values as a function of his experimental variables. In so far as the MunseIl system does represent equal color and saturation spacing, the procedure is satisfactory. When, however, functional relations break down, it is impossible to say whether this is due to a real phenomenon or an inadequacy of the system (see, for example, SEL.F, 1959, p. 135). The C.I.E. system was chosen in this investigation because of its wide applicability and acceptance. This system does not purport, however, to represent equal hue or saturation steps by equal distances, and agreement upon a suitable transformation for such purposes is yet to be realized. The question of functional relations can be considered bearing this limitation in mind.
INDUCING
COLOR
FIG. 12. The data for various luminance ratios plotted on the Maxwell equal-chromaticity diagram. The insert gives the distance from llluminant A of Maxwell data points for various luminance ratios.
The increase in saturation with size of inducing field has been shown, and it is noted that the function was not linear on the C.I.E. diagram but showed proportionately greater increase with the largest field size. Various transformations of the data were attempted as well as plots of the raw data, but positively increasing curvilinear functions always resulted. Since, in this investigation, increasing size of inducing fields was always accompanied by decreasing sizes of induced fields, this relation may reflect the change in receptor disttibution. It is thus possible that, for a constant retinal area, saturation is a Iinear function of inducing size, but that more color is induced in areas concentrated on the fovea1 centralis than in those surrounding it.
519
Factors Affecting Induced Color
Transfo~ations of the data on varying luminance ratios resulted in approximately linear functions relating the luminance ratio to the amount of color induced. Two examples are given. Figure 12 shows the data plotted on the Maxwell triangle (JVDD, 1935); the insert gives the distances of the various data points from Illuminant A as a function of luminance ratio. The amount of color increases proportionately to the ratio, with the inducing colors that are most similar to Illuminant A, the red and yellow, yielding the least amounts. This last point could not be predicted from the triangle since the red inducing color lies farthest from Illuminant A on the triangle and should on this basis yield the most color.2 Hurvich and Jameson’s transformations of the C.I.E. values are given in the next two figures.3 Figure 13 shows the actual values of change in color response from that of Illuminant A for the various luminance ratios (JAMESON and HURVICH, 1961);once again approximately linear functions are found. Also given for each inducing color are its GREEN-O.629 0.14
-
o-12
-
0.10
-
BLUE -0.251
0.10 0.08
0.06
0.06 0.00 0.10 0.12 o-14i 0.5 -
2 LUMINANCE
RATIO
w
0.5
LUMINANCE
RATIO
FIG. 13. Data transformed into Hurvich and Jameson’s system of color responses. The abscissa gives luminance ratios; the ordinate, the change from Illuminant A in red-green and yellow-blue responses. Red-green responses for each inducing color are plotted at the left; yellow-blue responses are at the right. R-G and Y-B for Illuminant A are assumed to be zero. s Judd’s method of predicting the induced colors utilizes a “neutral” point, calculated from the chromaticity values of the total field, which would be different for the various inducing colors. The distance from the inducing color to the neutral point is used to predict the amount of color induced (JUDD, 1940, 1960). An empirical determination of the neutral point was made for the conditions of this experiment. The chromaticity values of the point that looked white did change with the inducing color, lying on the green side of Illuminant A for the green-inducing color and on the red side for the red. The amount of change, however, was slight, particularly for the red and yellow, and would not influence the predicted chromaticities. 3 Values are calculated assuming that the eye is completely adapted to Illuminant A; the red-green and blue-yellow responses to Illuminant A are thus both zero. This is comparable to the analysis of JAMESOW and HURVICH (1961) but is probably an over-simpli~~ation, as they would no doubt agree, since Ill~inant A never appears completely white.
510
Jo ANN
S. KINNI.~
chromatic response values for red-green and yellow-blue. For example, the green-inducing color has the largest green component (-0629 R-G) and it induced the most red, while the yellow has the smallest red component (+0.078 R-G) and induced the least green. Differences in the Y-B responses are less both for the inducing and induced colors. Figure 14 shows the data plotted in the color specification system of HURVICH and JAMESON(1956). In this presentation, equal angles represent equal hue steps, while equal distances from the center are equal saturation steps. Illuminant A is represented by the center of the circle and the inducing colors by the solid triangles. The data points for the induced colors move out from the center, away from the inducing color, in an orderly progression as the luminance ratio is increased.
‘,
‘\,$ /
FIG.
/
‘,
:,
,,
\ -0.1
,,
14. The color specification system of Hurvich and Jameson.
Data points are colors induced by various luminance ratios of the inducing colors.
A comparison of the data from this experiment with mathematical predictions derived from various theories is beyond the scope of this paper. However, the author would like to point out the conceptual advantage of the polar plot of Hurvich and Jameson in the ease with which the color relations can be visualized. This ease of con~eptua~zation should be a factor in evaluating the utility of a system. Various theories have been proposed to account for color contrast, but modern versions of them differ mainly in the terminology used rather than basic conceptions. Agreement is widespread that there is a physiological basis for contrast rather than the error of judgment
Factors Affecting induced Color
521
that Helmholtz proposed. 4 The fundamental principle in many modern theories is that retinal areas adjacent to, but not directly stimulated by, the surround color show decreased sensitivity to the wavelengths of the surround color and increased sensitivity to the other wavelengths. At the physiolo~cal level, this change in sensitivity could be decreased response to the stimulating wavelengths (SELF, 1959; FLOCKS, 1960), through adaptation, or increased response to remaining wavelengths through opponent activity (HURVICH and JAMESON,1961) or both, Since the net result is the same, these data on the appearance of the colors cannot be used to support one or the other interpretation. For example, it has been shown here that the induced color changes from that of Illuminant A toward that of the complement of the inducing color as the luminance of the inducing color is increased relative to that of the induced. This phenomenon may be viewed as a case of increasing adaptation to the inducing wavelengths and the consequent depression of responsiveness to these components in the response to Illuminant A. On the other hand, the phenomenon may be viewed as a case of greater opponent activity induced into the focal area, thereby changing its appearance. The older argument, that the instantaneous appearance of color contrast contradicted the adaptation theory, has been discarded due to the results on rapid adaptation times (SCHOUTENand ORNSTBIN,1939). Therefore, no attempt was made in this investigation to retain a division between simultaneous and rapid successive contrast. Nevertheless, it was observed casually that there appeared to be temporal differences among the inducing colors and perhaps an investigation of these factors might help differen~ate between the two physiological theories. SUMMARY An experimental investigation of the factors affecting induced color was made by having observers compare the color induced into a field of Ill~nant A with another field of actual colored light. Four inducing colors, red, yellow, green and blue, were studied; these colors were varied in size, purity and luminance ratio to the induced field. Results are given both in terms of the C.I.E. values of the comparison field that yielded the same color as the induced color, and in terms of the luminance of the comparison field required to match the induced field in brightness, The amount of color induced increased as the size, lu~nan~ ratio, and, to a lesser extent, the purity of the inducing color were increased. The brightness of the induced color decreased with increasing luminance ratio. The effects of single parameters were found to be cumulative.
*JUDD (1960) attempts to retain HELMHOLTZ’S explanation (1924)by rephrasing it to include a discounting of the illumination on the scene, the discounted value being some kind of average of the total colors received from the scene. Since this explanation is on a conceptual rather than a physiological level, it is not included here.
.lo ANN S. KINN~\
522
APPENDIX C.I.E.
VALUES OF INI)UCED COLOR
Inducing Color-Green
(Wratten #60i-65A)x
Size
Luminance Ratio (Inducing~Induc~d} 0 --_~___
Purity
l/2 X
MS
__MC
---JK
___-FD
~-
__.?
s
1.2/l
2/l
__
P O-3602 0.3736 0.3853
z
.r
Y
0.1621 0.1553 O-1494
0*4817
0.3521
01662
0.3861 I+3883 0.3952
01014 0.1037 0*1109
0.5565
0.3646
00788
0.3752 0.3907 O-3948
0.1107 o-1 192 0.1215
0.5428
0.3567
0.1005
z
all color A+color 5A -t color
0.4621
?’ 0.3918
all color A -t color 5A + color
0.4773
0.4033
0.1194
all color A + color SA + color
0.4751
04003
0.1246
~_. 0.4857
04093
0.1050
0.5293 0.5121 0.4995
0.3919 0.4038 o-4064
0.0788 0.0841 0.0941
0.5405
0.3725
00870
0.4750
0.4012
0.1238
0.5084 0.4953 0.4856
0.3784 0.3891 0.3954
O-1132 0.1156 0.1190
0.5304
03615
0.1081
all color A + color 5A + color
Mean of 4 O’s all color A -_I-color 5A -i- color
01461
0.4777 0.4711 0.4653 0.5125 0*5081 0.4939 _^0.5142 0.4901 0.4837
Inducing Color-Blue
(Wratten #44A)-4”
--
-
-____
Size
Luminance Ratio (Inducing/Induced) 0 -
Purity
MS
all color A + color 5A + color
MC
112
1.2/l
2/l
X 0.4750
Y 0.4105
X
0.5075 0.5091 0.4883
Y 04085 0.4223 0.4097
2
01144
@0840 @0686 0*1020
0.5242
Y 04075
0.0683
all color A + color 5A + color
0.4744
o-4106
0.1151
0.5082 0.5140 0.5010
04085 04081 04089
0.0833 0.0779 0.0900
0.5272
0.4073
0.0655
JK
all color A + color 5A + color
0.4757
0*4105
0.1138
O-5126 O-5053 0.4954
04082 04087 0.4093
0.0792 0.0860 o-0954
0.5413
0.4064
PO523
FD
all color A + color 5A + color
0.4840
04051
0.1109
0.5347 0.3947 0.5242 04075 0.5050 0.4348 --__
0*0706 00683 0.0602
0.5550
0.3906
0.0544
0.4773
04092
0.1135
0.5157 0.5132 o-4974
0.0793 0.0752 0*0869
0.5369
0.4030
00601
Mean of 4 O’s all color A _t color 5A -t color
2
X
04050 O-4116 0.4157
z
Factors Aikting Inducing Color-Yellow
523
Induced Color (Wratten # 16)--4”
size
Luminance Ratio (Inducing/Induced) 1.2/l
0
Purity
Z
x
Y
Z
MS
All color A f color 5A + color
0.4284
04085
01631
04150 0.4284 0.4194
04058 04085 04067
0.1792 0.1631 0.1739
0.3816
0.3762
0.2422
MC
all color A + color 5A + color
0.4374
0.4104
0.1522
0.4261 0.4261 04150
04081 0.4081 0.4058
0.1658 0.1658 0.1792
0.3720
0.3532
0.2748
JK
all color A + color 5A -k color
04418
0.4113
0.1468
04261 0.4150 0.3928
0.4081 0.4058 04012
0.1658 0.1792 0.2060
0.3833
0.3860
0.2307
FD
all color A + color 5A + color
0.4374
0.4104
01522
0.3955 04004 @4294
0.3916 04043 0.4335
0.2129 0.1953 0.1371
0.3883
0.3882
0.2235
0.4362
0.4102
0.1536
0.4157 04175 0.4142
04034 04067 0.4118
0.1809 0.1758 0.1741
0.3813
0.3759
0.2428
l/2
Y
X
Mean of 4 O’s all color A + color 5A + color
X
Z
Inducing Color-Red
Y
(Wratten #33)--4”
2/l
Size
Luminance Ratio (Inducing/Induced) 1*2/l
0
Purity X
Y
Z
X
Y
z
X
Y
z
MS
all color A + color 5A -t color
0.4334
0.4272
0.1394
0.4126 0.4205 0.4288
04405 0.4355 0.4302
0.1469 0.1440 0.1411
0.4012
04478
0.1510
MC
all color A + color 5A + color
0.4500
0.4160
0.1340
0.4365 0.4298 0.4269
0.4366 04467 0.4510
0.1268 0.1235 0.1220
0.4287
04484
0.1229
JK
all color A + color 5A + color
0.4365
04366
0.1268
0.4227 0.4196 0.4152
0.4573 O-4620 0.4686
0.1200 0.1184 0.1162
0.3693
0.5373
0.0933
FD
all color A + color 5A + color
0.4334
04272
0.1394
0.4177 0.4152 04425
0.4648 0.4686 0.4851
0.1175 0.1162 0.0724
0.3956
0.4979
0.1065
0.4383
0.4268
0.1349
0.4224 0.4213 0.4284
04498 0.4532 0.4587
0.1278 0.1255 01129
0.3987
0.4829
0.1184
Mean of 4 O’s all color A + color 5A + color
l/2
2/l
KK
Jo ANN
524
S. KINNEY
Values for various sizes of Inducing Field-Purity Inducing Filter
5A i- color; Luminance ratio 1.2/l
Size 3” 4’ _~______~~__~_________._.-_..__---_-
0 X
Z
s
0.1138 0.1066 0.1053 0.0974
42 ’ -. Z
X
0.4883 0.5010 04954 0.5050
Y 0.4097 0.4089 0.4093 0.4348
0.1020 0.0900 0.0954 0.0602
Z
MS MC JK FD
0.4757 0.4834 0.4848 0.4786
Y 0.4105 0.4100 04099 0.4239
60 + 65A MS MC JK FD
0.4621 0.4804 0.4653 0.4715
0.3918 0.3969 0.3853 0.4122
0.1461 0.1226 0.1494 0.1163
0.4653 0.4939 0.4837 0.4995
0.3853 0.3952 0.3948 0.4064
0.1494 0.1109 0.1215 0.0941
0.4721 0.5032 0.5174 0.5267
0.3715 0.3823 0.3730 0.3671
0.1564 0.1146 0.1095 0.1062
16
MS MC JK FD
0.4261 0.4351 0.4261 0.4322
04081 0.4099 04081 0.4343
0.1658 0.1550 0.1658 0.1335
0.4194 0.4150 0.3928 0.4294
0.4067 0.4058 0.4012 0.4335
0.1739 0.1792 0.2060 0.1371
0.3928 0.4061 0.3708 04061
0.4012 0.4039 0.3966 0.4039
0.2060 0.1900 0.2326 0.1900
33
MS MC JK FD
0.4551 04442 0.4374 0.4312
0.4127 0.4200 0.4241 0.4288
0.1322 0.1358 0.1385 0.1400
0.4288 0.4269 0.4152 04425
0.4302 0.4510 0.4686 0.4851 -----
0.1411 0.1220 0.1162 0.0724
0.3970 0.3823 0.3417 0.3960
0.4505 0.5179 0.5787 0.5793
0.1525 0.0998 0.0796 0.0247
Mean of 4 observers 44A 0.4806 60 + 65A 0.4698 16 0.4299 33 04420
0.4136 0.3966 0.4151 0.4214
0.1058 0.1336 0.1550 0.1366
0.4974 0.4856 0.4142 0.4284
0.4157 0.3954 0.4118 0.4587
0.0869 0.1190 0.1741 0.1129
0.5260 0.5048 0.3940 0.3792
0.4173 0.3735 0.4014 0.5316
0.0567 0.1217 0.2046 0.0892
44A
Values for Maximum Color induced-Size: Inducing Filter
4;E”; Purity: All color;
X
Y
z
MS MC JK FTI
0.5316 0.5978 06095 0.5943
0.4070 0.4014 0.3900 0.3235
0.0614 OWO8 OWO6 0.0823
60 + 65A MS MC JK FD
0.4963 0.5866 0.5708 0.5990
0.3225 0.3500 0.3386 0.3204
0.1812 0.0634 0.0906 0.0806
16
MS MC JK FD
0.3519 0.3386 0.3192 0.3482
0.3544 0.3279 0.3336 0.3697
0.2937 0.3335 0.3472 0.2821
33
MS MC JK FD
0.3180 0.2776 0.2776 0.3307
0.5011 0.6748 0.6748 0.5953 ~____.
0.1809 0.0476 0.0476 0.0740
44A
______~ 44A 60 + 65A 16 33
0
0.5833 0.5632 0.3395 0.3010
Mean 0.3805 0.3329 0.3464 0.6115
0.0363 0.1039 0.3141 0.0875
0.5097 0.5338 0.5272 0.5335
Y 0.4084 04069 04073 0.4465
0.0820 0.0593 0.0655 0.0201
Luminance ratio: 2/l
Factors Affecting Induced Color
525
REFERENCES BOYNTON,R. M. (1960). Theory of color vision. J. opf. Sot. Amer. 50, 929-944. DIAMOND, A. L. (1953). Fovea1 simultaneous brightness contrast as a function of inducing- and test-field luminances. J. exp. Psychol. 45, 304-314. EVANS, R. M. (1943). Visual processes and color photography. J. opt. Sot. Amer. 33, 579-614. FLOCKS, M. (1960). The physiologic basis of simultaneous color contrast. Trans. Pucif: Cst oto-ophthal. Sot. 41, 153-177. HEINEMANN, E. G. (1955). Simultaneous brightness induction as a function of inducing- and test-field luminances. J. exp. Psychol. 50, 89-96. v. HELMHOLTZ,H. (1924). Treatise on Physiological Optics, Vol. II, pp. 264-301. (Translated from the third German Edition by J. P. C. SOUTHALL.) Optical Society of America. HELSON, H. and SELF, C. (1961). A study ofcoloured shadows. Maxwell Colour Centenary, London. HESS, C. and PRETORI, H. (1894). Messende Untersuchungen iiber die Gesetzmlssigkeit des simultanen Helligkeitscontrastes, v. Gruefes Arch. Ophthal. 40, l-24. HURVICH, L. M. and JAMESON, D. (1956). Some quantitative aspects of an opponent-colors theory. IV. A Psychological color specification system. J. opt. Sot. Amer. 46, 416-421. JAMESON,D. and HURVICH, L. M. (1959). Perceived color and its dependence on focal, surrounding, and preceding stimulus variables. J. opt. Sot. Amer. 49, 890-898. JAMESON,D. and HURVICH, L. M. (1961). Opponent chromatic induction: experimental evaluation and theoretical account. J. opt. Sot. Amer. 51, 46-53. JUDD, D. B. (1935). A Maxwell triangle yielding uniform chromaticity scales. J. opt. Sot. Amer. 25, 24-35. JUDD, D. B. (1940). Hue saturation and lightness of surface colors with chromatic illumination. J. opt. Sot. Amer. 30, 2-32. JUDD, D. B. (1960). Appraisal of Land’s work on two-primary projections. J. opt. Sot. Amer. 50,254-268. KARP, A. (1959). Colour-image synthesis with two unorthodox primaries. Nature, Lond. 184, 710-712. KIRSCHMANN, A. (1890). Uber die quantitativen Verhlltnisse des simultanen Helligkeits- und FarbenContrastes. Psycho/. Stud. (W&t), 6, 417491. LAND, E. H. (1959a). Color vision and the natural image. Part I. Proc. nat. Acud. Sci., Wash., 45, 115-129. LAND, E. H. (1959b). Color vision and the natural image. Part II. Proc. nut. Acud. Sci., Wash., 45,636644. SCHOUTEN,J. F. and ORNSTEIN, L. S. (1939). Measurements on direct and indirect adaptation by means of a binocular method. J. opt. Sot. Amer. 29, 168-182. SELF, H. C. (1959). A quantitative study of colored shadows. Ph.D. dissertation, University of Texas, Austin, Texas. WALLS, G. L. (1960). Land! Land! Psycho/. Bull. 57, 2948. WILSON, M. H. and BROCKLEBANK,R. W. (1960). Two-colour projection phenomena. J. photogr. Sci. 8, 142-150. WOODWORTH, R. S. (1938). Experimental Psychology, pp. 567-571. Henry Holt and Co., New York.
Vol. 2. pp. 503-525.
Pergamon
FACTORS
Press
1962.
Printed inGreat Britain.
AFFECTING
INDUCED
COLOR
Jo ANN S. KINNEY U.S. Naval Medical Research Laboratory, (Received
Groton, Connecticut
3 August 1962)
Abstract-The amount of color induced into a field of Illuminant A was determined for four inducing colors, red, yellow, green and blue, by having observers compare the induced color with a field of actual colored light. The results, given in C. I. E. values, show that the amount of color induced increases as the size of the inducing field is increased, as the luminance ratio between inducing and induced fields is increased, and, to a small extent, as the purity of the inducing color is increased. R&un~&-La quantite de couleur induite dans un champ de l’etalon colorimetrique A fut mesuree pour quatre couleurs inductrices, rouge, jaune, verte et bleue, en faisant comparer aux observateurs la couleur induite avec un champ de lumitre reellement color&e. Les resultats, don& en valeurs C.I.E., montrent que la quantite de couleur induite augmente avec la dimension du champ inducteur, avec le rapport des luminances entre champs induit et inducteur, et pour une faible part avec la purete de la couleur inductrice. Zusammenfassung-Indem die Beobachter die induzierte Farbe mit einem Feld, das mit einer reinen Farbe erleuchtet war, verglichen, wurde der Anteil der induzierten Farbe in einem Feld der Lichtart A fur vier Farben, nlmlich Rot, Gelb, Griin und Blau gemessen. Die Ergebnisse, die im C.I.E.-System dargestellt sind, zeigen, dass der Anteil der induzierten Farbe in der gleichen Weise ansteigt, wie die Grosse des induzierenden Feldes wlchst, wie der Helligkeitsunterschied zwischen dem induzierenden und dem induzierten Felde zunimmt, und in geringem Masse wie die Reinheit der induzierenden Farbe grosser wird.
A MAJORcontribution by LAND (1959a, b) in his demonstrations of two-color projection has been to restimulate interest in the phenomenon of induced color. Within the last few years, reviews of the subject by WALLS (1960) and by JUDD (1960) and experimental data by SELF (1959), WILSON and BROCKLEBANK (1960), KARP (1959), and JAMESON and HURVICH (1959, 1961) have been reported. Compared with the previous fifty years of inactivity, the change is impressive. On the other hand, little of the recent data is applicable to the formulation of laws stating how much and what kind of color is induced under various conditions. One reason is that many of the investigators were interested in the complex stimulus conditions used by Land. Another is that much of the newer work has utilized the technique of color-naming, a method that does not lend itself readily to quantification. At the end of the nineteenth century, investigators did attempt to find generalities for predicting the variables underlying induced color. The classical laws of KIRscHMANN (1890) stated that the saturation of the induced color increased with increasing size and increasing saturation of inducing color and with decreasing brightness contrast between the two areas. Although these laws are still widely quoted, few attempts have been made to verify them. SELF (1959) investigated the effect of purity and luminance ratio on induced color and found that saturation increased with increasing purity and with increasing luminance of inducing field. JAMESON and HURVICH (1959) also cite examples of increased saturation with increased surround luminance. WALLS (1960) disagrees with Kirschmann’s law 503
concerning purity of inducing color, stating that highly saturated colors are seen when the inducing color is tlooded with dim white light. The particular hue induced under simple stimulus conditions has not received much attention, since it has been known since Fechner to be roughly complementary to the inducing hue and since individual differences in sensitivity and pigmentation easily account
for the variations. Self, using Illuminant C as the induced field, also concludes that the hues are complementary and do not change with the purity or the luminance of the inducing color. The purpose of this investigation, therefore, was to obtain quantitative data on the factors influencing induced color by having observers compare the color induced in a given area with that of a field of actual colored light. The effect of the size, purity and luminance of four inducing colors was studied for an induced field of Illuminant A. APPARATUS
A Bausch & Lomb projection calorimeter was used to provide the stimuli. The colorimeter consists of three separate projecting systems from a single light-source, an inside frosted 300W lamp of 2854°K. The light from each projecting system can be varied in intensity by the setting of diaphragm blades and, in form and spectral composition, by appropriate templates and filters. In addition, filter holders are provided in an out-of-focus position to yield an additive mixture of the light transmitted by two filters. The position of the two filters relative to the path of light can be varied in small steps between the two end positions; the spectral composition of the projected light can thus be varied from that transmitted by one filter to the other with all mixtures in between. A group of approximately thirty Wratten filters, mounted in cover glass, gave comprehensive control of chromaticity values. The spectral transmissions of these filters were measured on a G.E. Spectrophotometer and C.I.E. values calculated for Illuminant A. Luminances of llluminant A on the screen were measured with an ultra-sensitive Spectra Brightness Spot meter. STIMULI
Figure 1 is a representation of the stimulus field. At the top is the field as it appeared when focused on a white Bainbridge board screen; at the bottom are the components of the field. Light from the first projector was filtered so that it provided a circular field of color with a vertical unlighted strip in the center. Light from the second projector was focused on the same area of the screen. Light from the third projector, used in conjunction with the movable filter holders and Wratten filters, provided the comparison field. Three stimulus parameters were investigated. First the size of the vertical unlighted strip was varied. The diagram shows the lo strip; a 2” strip and a r strip were also studied. The field size remained constant at 5”, so as the strip was decreased in size the colored or inducing area varied from 3” to 4$“. Secondly, the purity of the colored light was varied by changing the amount of Illuminant A from the second projector. At one extreme five times as much Illuminant A as colored light was used, resulting in a very desaturated inducing stimulus. At the other extreme, arbitrarily defined as maximum purity, all Illuminant A was removed from the semi-circular fields. This is indicated in the diagram by the dashed lines; under this condition only light from the second projector was in the center strip.
505
Factors Affecting Induced Color
The third parameter was the luminance ratio between the semi-circular fields and the center strip. Not all combinations of all parameters were investigated. In general, two parameters were held constant, while the third was varied. The effect of purity and luminance ratio was studied for the medium, 1” strip ; with purity the variable, the luminance ratio was 1.2/l ; with varying ratios, purity was maximum. The effect of the size of the inducing field was determined for the minimum purity and 1*2/l luminance ratio. When evidence of interactions between parameters was found, other combinations were studied. COMPARISON FIELD
INDUC~ON FIELD
Projector FIG.
1.
I
Projector 3
Projector 2
The stimulus field, as it appeared to the observer, and its components.
Four different inducing colors were investigated. Table 1 gives the chromaticity values of these four colors together with the values for the various purities, or mixtures with Illuminant A, and the maximum luminance used. TABLE
Purity condition
Red #33 Yellow # 16 Green #60+#65A Blue #44A
1. DESCRIPTION
Y
06766 0.5590 0.0843 0.1280
0.2666 0.4386 0.6509 0.3463
COLORS
X
Y
z
X
Y
z
Max. Lumill. used ft-L
0.5860 0.5011 0.3077 0.2748
0.3223 0.4228 0.5012 0.3744
0.0917 0.0761 0.1911 0.3507
0.5012 0.4651 @4072 0.3869
0.3745 0.4124 0.4346 0.3961
0.1243 0.1225 0.1582 0.2170
0,260 O-260 0.094 0.260
Equal amounts Color & Illum. A
Maximum x
OF INDUCING
I 0.0568 O+-rO23 0.2648 0.5257
5 times as much Illurn. A
Luminance levels of the inducing colors varied around 0.1 f&L. Preliminary investigation revealed that the absolute level was not a factor in the amount of color induced as long as the ratio between inducing and induced fields was constant. Nevertheless, the luminances of the red, blue and yellow were kept the same for ease of comparison; the luminances of the green-inducing color were lower, due to the lower transmission of the green filter.
PROCEDURE
The observer viewed the screen binocularly from a seat 10 ft away. Between presentations a shutter blocked the colored light from the first and third projecting systems so that the field consisted of Illuminant A from the second projector viewed against a dim surround of 0.001 ft-L of Illuminant A. The total field was exposed from 2 to 3 set with 10 set between exposures. Data were taken for four observers, all of whom had normal color vision. The color induced in the center strip was compared with the actual colored light in the comparison field, which could be varied in hue, saturation and brightness. The method of constant stimuli was used to determine saturation limens. The comparison field was set at given proportions of color;Illuminant A and the observer was asked, in one series, whether the induced color was more saturated, and, in another series, whether the comparison color was more saturated. He was instructed to glance briefly from one to the other to make his comparisons. Ten judgments at each of five settings of the comparison Before saturation judgments began, the comfield were used in each series of judgments. parison field was varied in brightness and hue until it appeared equal to the induced color in these respects.
96 96
90
\f I \\
E
I
0 50 .z f 40 0 p 30 'i: al y 20 It
1 l
I\ I\
IO
I
2
tll’JJ~\.“‘~’
& Al;
0.05
A
I
SIZE INDUCING
9 I
--
OF FIELD 30
-
40
-___-
4 3/40
0
I \ 4
\
I’ I
a
1.
\
I
\
I
0.15
0.25
0.35 Proportion
0.45 of wrotten
0.55
0.65
# 21
FIG. 2. Sample data showing the effect of (a) the size of the inducing field, and, opposite, (b) the
purity of the inducing color, (c) the luminance ratio between inducing and induced fields.
(a>
507
Factors Affecting Induced Color
96 96
90
$30 E?O S60 -: 50 B E 40 :: a 30 .
---
-017
0 -033 10
0 --0.50 & ---
Maximum
@360
4 2 0.15
0.25
Proportion
0.35
09
0.45
of Wratten
# 21
98 96
E: 80 E F 70 2 60
!
I \ \
!
I
! f
il
5 2
1
r 8 f
All A
0.15
v
II
_____ 0I
- -
I
‘, I
1 \ \
‘:
IIL
-
,
I\
I ,
RATIO
INDUCING TO INDUCED FIELDS
1 \
I\
II
ace
\I
LUMINANCE
I
10
I
I.2 to
to I to I
---4
I
\
,
t
I
\
, 0.25
0.35 Proportion
o-45 of
Wratten
(121
All Filtered
@I
RESULTS Figure 2 shows examples of the individual data given to show the method of obtaining it and the type of saturation differences found. The inducing color is blue, Wratten #44A, for all. The light in the comparison field is a mixture of Wratten #21 (Dominant A=594 m,u) and a neutral filter; the c~omatici~ values of the comparison field thus lie on a line connecting Illuminant A and 594 rnp. Figure 2a shows the data for one observer for the three sizes of inducing field in terms of the percentage of times the comparison and the induced fields were judged to be more saturated. In all of the plots on probabi~ty paper there are pairs of intersecting lines; the
II
508
Jo ANN S. KINNEY
one with the negative sfope of each pair refers to judgments of the induced field; the one with positive slope refers to those of the comparison field. For example, with the 3” field, when the comparison field was set at a mixture of twenty per cent color (Wratten #21), eighty per cent Illuminant A, the induced field was judged to be more saturated ninety per cent of the time, while at a setting of thirty per cent color, seventy per cent llluminant A, the comparison field was more saturated 100 per cent of the time. The proportion of color in the mixture increases as the size of the inducing field increases and the amount of the increase is such that there is no overlap of judgments from one size to the next.
FIG. 3. C.I.E. diagram of the data for the four observers with the green-inducing various luminance ratios.
color at
Figure 2b is a sample of the data for another observer with purity the parameter; the axes are the same. Saturation limens increase with increasing purity, but the effect is small; the judgments overlap each other throughout the entire range from an inducing color very near Illuminant A to one close to the spectrum locus. Figure 2c shows the data for different luminance ratios between inducing and induced fields. The proportion of color needed in the comparison field increases from twenty per cent to eighty-two per cent as the luminance ratio between inducing and induced fields is increased from O-5 to 4.0. The proportion of color to Illuminant A at the midpoint between fifty per cent limens for induction and comparison fields was converted into C.I.E. values for each of the experimental conditions. Fjg. 3 shows an example of the data for the four observers on a C.I.E.
509
Factors Affecting Induced Color
diagram. The inducing color is green at its maximum purity and 4” size; the experimental parameter is the luminance ratio between inducing and induced fields. The data for the four O’s are plotted on four lines, since each 0 used a different Alter, mixed with Illuminant A, in the comparison field. This result is typical of the inter-observer differences found throughout the experiment; that is, the effect of experimental parameters in increasing or decreasing the saturation of the induced color was the same for all O’s, but the hue of the color induced varied consistently with the particular 0. For this reason, the individual data, given in C.I.E. values, are tabulated in the Appendix and the average C.I.E. values for the four O’s are shown in the remaining figures.
MEDWM
SIZE
MAXIMUM PURITY LUM fNANCE RATIO
0.6
X
I to2
0
I.210 I
o-5
Y
0.4
595 600
\
to RED
WHITE
INDUCING \ 67, y=O.267 0
D.4
0.5
06
X FIG. 4. Portion of C.I.E. diagram showing the average data for various luminance ratios of inducing to induced fields for the four inducing colors.
Effect of Luminance Ratio. Figure 4 gives a portion of the C.I.E. diagram on which the average data for the four observers have been plotted to show the effect of the luminance ratio between inducing and induced fields. The other experimental conditions are constant, size at 4”, and purity at its maximum value. In addition, lines are indicated connecting Illuminant A to the four inducing colors, all of which, with the exception of the yellow, lie beyond the limits of this portion of the diagram at maximum purity. When the luminance ratio is l/2; that is, the induced field is twice as bright as the inducing field, all the induced colors lie very close to Ilhuninant A. As the luminance of the inducing field, relative to the induced, is increased, the induced colors move away from Illuminant A in a direction that is roughly opposite to the inducing color. The opposition is only approximate, since if perfect all points would lie on the lines. Relative to the white point
510
Jo
ANN
KINNFY
S.
(x=y-O-33) on the C.I.E. diagram, the change is primarily one of hue, the colors changing from a hue close to that of Illuminant A toward the hue of the complement of the inducing color as the luminance ratio is increased. EfSect of Size. Figure 5 shows a portion of the C.I.E. diagram for the experimental parameter, size of inducing field. The inducing colors, all at the minimum purity condition, or a mixture with five times as much Illuminant A as color, are indicated by the triangles. For each inducing color, the amount of color induced increases as the size of the inducing field is increased. Also, in each case the color induced by the largest field size, 4$“, is farther away from Illuminant A on the diagram than is the inducing color itself. Once again, when compared to an equal energy white point, the hues of the induced colors change toward the complement. -
-
-____-..
555
560 \
SIZE /NDUCfNG
OF F/E/d
Y
x0
\
0.6
0.5
Y #60t65A+
5A
0.4
#-33+
cl.3
0.4
5A
0~6
0.5 X
FIG. 5. Portion of the C.I.E. diagram showing the average data for the various sizes of inducing fields.
The amount of increase in color on the C.I.E. diagram does not relate linearly to the field size since the distances between the values for the 4” and 4F fields are greater than that between the 3” and 4” fields. Efict of Purity. Figure 6 shows the data for different purities of each inducing color. Purities range in each case from a color very close to the spectrum locus to one near Illuminant A. The induced colors, however, show much less variation. The colors induced by the blue and green do show an increase in saturation with increasing purity although the differences are not as great as those shown for the other experimental parameters. The colors induced by red and yellow, on the other hand, show little or no effect of purity.
511
Factors Affecting Induced Color
Inspection of the individual data for red and yellow, given in the Appendix, reveals that differences between purities exist but are not the same for each observer. For some observers, the major shift is one of hue; for othas, the minimum purity condition yields the most color. INDUCJNG COLORS A A
560
565
l
\
INDUCED COLORS X
PURITY 5A+Color A+ Color
0 l
All Color
570
to GREEN
\
575
:EN ,P
to BLUE
(#44A)
\ l
\
apoo \05
WHITE 5
L-
Ll
FIG. 6. Portion of the C.I.E. diagram showing the average data for different purities of inducing colors.
Interactions between Parameters. Since the data for variations of a single parameter with the other two held constant gave clearcut relations, various other combinations of parameters were investigated to determine whether or not the effects were cumulative. A number of combinations are possible, but two were studied in detail, the combination of parameters that, when presented singly, yielded the most color and the least color. Figure 7 shows a C.I.E. diagram of the effects obtained by these two combinations of parameters. The results for a combination of conditions which yielded the maximum amount of color are shown by the crosses. These conditions were the largest-sized inducing field, maximum purity and a 2/l luminance ratio between inducing and induced fields. Also given on the diagram are the inducing colors, specified by their filter numbers, and the complements of the inducing colors, shown by straight lines drawn from the inducing color through an equal energy white point to the spectrum locus. Large amounts of color are induced by these conditions, revealing the effects of single parameters to be cumulative. Furthermore, the induced hues have changed greatly from that of the dominant wavelength of Illu~nant A. Viewed in connection with the specified white, the induced hues for each of the four inducing colors have moved away from the hue of Illuminant A towards that of the complement; under these conditions the movement has been approximately half-way to the complement.
.I() ANN S. KINNEY
511
The use of the term “maximum induced color” refers only to the conditions of this study and does not imply that no further color would be found if the ranges of the experimental parameters were increased. A few increases in range were indeed tried, and Fig. 2c has shown an example of further increase in color with a 4/l luminance ratio. In general, however, extreme conditions were difficult to investigate and were not included. The increased luminance ratio, for example, resulted in such dark colors (see next section) that judgments became difficult.
._ _~__~ I
A
INDUCING COLORS INDUCED COLORS t .
0
0.10
3800.20
0.30
0.40 x
0.50
MAXIMUM MINIMUM
of30
0.70
I
0+30
FIG. 7. C.I.E. diagram showing the chromaticity
values of largest and smallest amounts of color induced under the conditions of this study.
The data for the least color are given in the diagram by the circles. With the minimum purity, smallest field size and smallest luminance ratio, the color induced by the green and the blue could be reduced considerably but could not be eliminated within the ranges used here. However, it was possible to obtain an induced field which was not noticeably different from Illuminant A by using the smallest field size and luminance ratio and the maximum purity for the red- and yellow-inducing colors. The next two examples of this effect are given in terms of the actual data, since the differences are so small that they are difficult to depict on the C.I.E. diagram. Figure 8 shows the percentage of responses for two observers for the yellow-inducing color. The abscissa is the proportion of filters #44A and #16 required for the comparison field to be judged bluer in one direction and yellower in the other than the induced color, (Since little or no color was induced, the usual saturation judgments could not be used.) For comparative
513
Factors Affecting Induced Color
purposes, data were also taken with no inducing field present; this was possible since a given proportion of #16 and ##A is a metamer of Illuminant A. For both observers, the maximum purity of the yellow-inducing hue gives comparable results to that of Illuminant A alone, while the mi~mum purity yielded judgments on the blue side of this match.
I
\
II
6
I
I-- lk i
\
1\ I 1 1.
: : : I :
PURITYOF INDUCING
FJELD
----
MAXIMUM MLWIMUM
-
NO INDUCING FIELD
J +-BLUER
PROPORTION OF FILTERS *44A
-+I6
YELLOWER+
FIG. 8. Comparison of the effect of minimum and maximum purity of the yellow-inducing color under conditions yielding small amounts of induced color.
Table 2 gives comparable data for the smallest size of the red-inducing color. The liminal values show that the minimum purity of the red-inducing color results in an induced hue that is slightly greener than that produced by the m~mum purity. In order to determine whether this reversal with purity was true in general for the redand yellow-inducing hues, other parameters were varied to increase the general level of color induced. This was done for the yellow-inducing color by using the largest-sized field and for the red by increasing the luminance ratio to 2/l. The average C.I.E. values are TABLE
2.
COMPARISON
OF LIMINAL
VALUES*
OF COLOR
INDUCING
Purities of #33 (Red) 5A+ color A + color Al1 color No inducing field
MS 0.322 O-326 0.336 0.336
INDUCED
Observers MC JK o-305 o-303 o-310 0.318
BY VARIOUS
PURITIES OF
3”
RED-
FIELD
O-296 O-307 0.322 0,313
FD
Mean
0.286 @288 O-284 0.320
0.302 o-306 0.313 0.322
* Units are proportion of #33 in mixture of #33 and #60+ indicate all 60+ 6.5A (green) and 1.0, all 33 (red).
#65A in comparison
Mean C.T.E. values X Y o-442 0-W 0448 0.455
o-421 0.420 0.417 0.413
field, Zero would
514
Jo
ANN
S.
KINNEY
given in Fig. 9. Under these conditions the colors induced by yellow and by red do behave comparably to the blue and green; the amount of color induced increases with the purity of the inducing cotor and the hue moves away from that of Illulninant A. For the red the major change is one of hue.1
PURITY l
OF INDUCING 5A+
COLOR
FIELD
j .; -1
0 A + COLOR ___....___
;
/
o.30/&&_---~---+.--
x
_.__./ ~__.__ .‘__
All
COLOR
-----LT_.._.+
FIG. 9. C.I.E. diagram showing the effect of various purities of red- and yellow-inducing colors under conditions yielding large amounts of induced color.
Thus, for the red- and yellow-inducing colors, conditions which result in little induced color reveal the minimum purity to be as effective or more so than the maximum. With conditions yielding large amounts of color, however, the maximum purity condition gains in effectiveness and becomes comparable to that found with the blue and green. This interaction can be seen in the individual data given in the Appendix. At these intermediate color conditions, the purity condjtion which gives the greatest amount of color varies with the individual. Induced Brightness. The colors induced under the various experimental conditions varied in brightness as well as chromaticity, and measures of the luminances at which the comparison field was set in order to appear comparable to the induced field are also available. Figure 10 gives these data for each of the four inducing colors as a function of the 1 The c&or induced by the less pure reds, described as a highly saturated pea green, proved difficult to match, since yellow-green filters of high purity are rare. Filters, or combination of filters which appeared to have the necessary saturation, were not yellow enough, and those with the proper hue were not saturated enough. Au acceptable combination, however, was found for the minimum purity condition by combining a green (#53) and a yellow (#12) filter, the resulting combination lying close to the Y-G spectral locus.
515
Factors Affecting induced Color Actual
Luminance
of
Induced
Field
NO
Induction
I.0 Color
..“----.
Red
O---O
7 f
Inducing
X----
&IO
:\
q
cl -;
$
Blue X
Yellow
-,--n
Green
t-t
White
a
4’ 2
E
0.6
:: .
2
I
s [email protected]
Actual
Luminance
Induced : z 1
Field
of
used
with Green
’ \
0
. . ‘:
‘a._ -0
z
0.065 Luminance
Oe56 of
Inducing
Field
0??6 (Ft.L.)
FIG. 10. The effect of the luminance ratio between inducing and induced fields upon the apparent brightness of the induced field. Measures are in terms of the luminance at which the comparison field was set.
luminance level. Also given are the data for a white field, taken under the same conditions as the colors, for comparative purposes. The graph at the left gives the data at the actual levels used; on the right the data are given in terms of ratios so that the green could be compared with the other colors. In all cases the induced field appeared dimmer than the comparison field since the surround of the former (the inducing field) was always greater than that of the latter (general background-0301 ft-L). As the luminance of the inducing field increases, the comparison field is set at progressively lower values to match the appearance of the induced field. Within the range used here the data are acceptably fitted by a straight line; the same line could be used to fit the blue, green and red, and a different line, with greater slope, the yellow and white. On a log-log plot, Fig. II, the curves fall rapidly as the luminance of the inducing
iNDUClNG
COLOR
.
RED
Q
BLUE
0
GREEN
03-
x
YELLOW
z
+
WMITE
\
+ x
a zel-i
LOGFIG.
LUMINANCE
RATIO
(INDUCING/INDUCED
FIELDS1
11. Apparent brightness data plotted on a log-log scale.
51 0
Jo
Awry S.
KINN~\I
field is increased beyond that of the induced. This drop is indicative of the fact that at higher luminance ratios the appearance of the induced field rapidly approaches black. The approach to black is more rapid for yellow and white than the other colors. The dotted line indicates the connection between the 1.0 ratio on the abscissa to the theoretical match of no brightness induction if the inducing/induced ratio were the same for the induced and comparison fields (OXlO1~0~13or 0*001/0.047).
DISCUSSION
A comparison of the results of this study with the classical laws of KIRSCHMANN(1890) on color contrast reveals agreement that the size of the inducing field is a major variable in the amount of color induced. Further agreement is found on the effect of the purity of the inducing color. Kirschmann stated that induced color increased with saturation although the function was one of diminishing returns. We find, in general, increased induced color with increased purity although the sizes of the differences are very small compared to the differences in inducing purities used. In addition it should be pointed out that it is possible to find induced colors that are more saturated than their inducing colors and to find combinations for which the least pure colors are the most effective. These facts, coupled with the small effect in general, help account for the continuing disagreement found in the literature on this question. Kirschmann’s third law, that greatest color is induced when there is no brightness contrast between inducing and induced fields, has not been upheld. Our results are, however, in agreement with all the newer work in the field; both SELF(1959) and JAMESON and HURVICH (1959) found more color induced with larger luminance ratios between inducing and induced fields. All investigators agree that the least amounts of color are induced when the induced field is the brighter; on the other hand, an upper limit is placed upon the increase of induced color as the luminance of the inducing field is increased, since with ratios of sufficient size the induced color appears black. This complication of induced brightness contrast is discussed below and was probably a factor in Kirschmann’s results. The shift in the hue of the induced color with the various experimental parameters, a result of this study, has not received much attention, since it is not found when a neutral stimulus is used in the induced area. The phenomenon, however, is part of the history of colored shadows and has been discussed by many (EVANS, 1943; KARP, 1959; WALLS, 1960). The direct stimulation of the induced area, in this case Illuminant A. cannot be discounted, and the resulting color appearance must be a mixture of the direct stimulation and the contrast color. In this investigation, using conditions which minimize the effect of the direct stimulation, it has been possible to show a shift in the appearance of Illuminant A approximately half-way toward the true complement of the inducing color. The color appearance of the complement only is probably a theoretical limit not actually attainable in practice. The result is, however, applicable to Land’s beautiful color renditions, since the appearance of the colors shifts dramatically under the various experimental conditions. The hue shift, coupled with brightness differences, yields colors of remarkable diversity. The color names employed to describe those colors induced by the blue, for example, would include canary yellow, antique gold, toast and Indian red. It should be remembered in this connection that no light from the inducing color, but only Illuminant A, was presented in the area under investigation; combinations of two illuminants in the same area open a further expanse of possible colors.
Factors Affecting Induced Color
517
The brightness induction effects found in this study relate closely to work of other investigators. Linear relations between apparent brightness of the test field and the luminance of the inducing field generally have been found with limited luminance ranges (HESS and PRETORI,1894; WOOLWORTH, 1938. More complete investigations over wide ranges have been made by DIAMOND(1953) and by HEINEMANN(1955). Both authors found a curvilinear function between apparent brightness of a test spot and inducing luminance on a log-log plot; for inducing luminances somewhat below the level of the test field the brightness is slightly reduced, while for luminances above the test field the reduction becomes much more rapid. The curves of the two authors differ in the rate of the drop found above the test field luminance. Diamond’s reductions are relatively gradual and show effects for more than two log units. On the other hand, Heinemann’s drop rapidly, and he states : “the effect of inducing fields whose luminance exceeds that of the test field by more than approximately O-1log unit cannot be measured; for inducing fields of greater luminance the test field appears darker than the ~ompa~son field for any suprathreshold luminance of the latter” (HEINEMANN,1955. This difference undoubtedly relates to the stimulus fields used by the investigators; Diamond’s inducing field was square with only one side adjacent to the test field, while that of Heinemann was circular and completely surrounded the test field. The curve found in this study (Fig. 11) is intermediate between Diamond’s and Heinemann’s in the extent of the drop with inducing luminance. With luminances of approximately one log unit or more the induced color appeared black and no measurements were possible. The spatial relations between inducing and induced fields were also intermediate to those of the two authors, since approximately eighty per cent of the induced field was immediately adjacent to the inducing. This analysis points up another variable, not investigated in this study, affecting induced color: the spatial relationship between the inducing and induced fields. JAMESONand HURVICH (1961) have studied this aspect and have shown that the amount of color induced increases with the amount of contiguity between inducing and induced fields. Further changes in the appearance of the induced color would be expected from the varying amounts of brightness-induction that result from different stimulus configurations. These investigations on b~~tness contrast have all been done using white light. To the knowledge of the author, there are no comparable, systematic studies dealing with the brightness-inducing qualities of various colors. The indication in these data that blue, green and red behave comparably in this respect, while yellow gives similar results to those of white, is interesting from the theoretical point of view, and lends support to interpretations, such as that of BOYNT~N (1960), that yellow and white cone functions are similar. A major di~culty in determining functional relations for parameters affecting induced colors is the lack of an adequate system of color-spacing in which to specify the results. Several alternatives are possible. First, one can specify strictly in terms of the operational measures used in matching the induced colors. Kirschmann’s data are given in degrees of color on the color disc; in this investigation such specification would be in the proportion of a colored filter used in comparison mixture. The obvious disadvantage of such a procedure is Jack of generality, since the relations will refer only to the particular colored paper or filters used. A second alternative is to specify the colors in one of the better known color systems; the disadvantage here is that one is restricted by the limitations of the system itself. Self chose
the Munsell system and plots Munsell values as a function of his experimental variables. In so far as the MunseIl system does represent equal color and saturation spacing, the procedure is satisfactory. When, however, functional relations break down, it is impossible to say whether this is due to a real phenomenon or an inadequacy of the system (see, for example, SEL.F, 1959, p. 135). The C.I.E. system was chosen in this investigation because of its wide applicability and acceptance. This system does not purport, however, to represent equal hue or saturation steps by equal distances, and agreement upon a suitable transformation for such purposes is yet to be realized. The question of functional relations can be considered bearing this limitation in mind.
INDUCING
COLOR
FIG. 12. The data for various luminance ratios plotted on the Maxwell equal-chromaticity diagram. The insert gives the distance from llluminant A of Maxwell data points for various luminance ratios.
The increase in saturation with size of inducing field has been shown, and it is noted that the function was not linear on the C.I.E. diagram but showed proportionately greater increase with the largest field size. Various transformations of the data were attempted as well as plots of the raw data, but positively increasing curvilinear functions always resulted. Since, in this investigation, increasing size of inducing fields was always accompanied by decreasing sizes of induced fields, this relation may reflect the change in receptor disttibution. It is thus possible that, for a constant retinal area, saturation is a Iinear function of inducing size, but that more color is induced in areas concentrated on the fovea1 centralis than in those surrounding it.
519
Factors Affecting Induced Color
Transfo~ations of the data on varying luminance ratios resulted in approximately linear functions relating the luminance ratio to the amount of color induced. Two examples are given. Figure 12 shows the data plotted on the Maxwell triangle (JVDD, 1935); the insert gives the distances of the various data points from Illuminant A as a function of luminance ratio. The amount of color increases proportionately to the ratio, with the inducing colors that are most similar to Illuminant A, the red and yellow, yielding the least amounts. This last point could not be predicted from the triangle since the red inducing color lies farthest from Illuminant A on the triangle and should on this basis yield the most color.2 Hurvich and Jameson’s transformations of the C.I.E. values are given in the next two figures.3 Figure 13 shows the actual values of change in color response from that of Illuminant A for the various luminance ratios (JAMESON and HURVICH, 1961);once again approximately linear functions are found. Also given for each inducing color are its GREEN-O.629 0.14
-
o-12
-
0.10
-
BLUE -0.251
0.10 0.08
0.06
0.06 0.00 0.10 0.12 o-14i 0.5 -
2 LUMINANCE
RATIO
w
0.5
LUMINANCE
RATIO
FIG. 13. Data transformed into Hurvich and Jameson’s system of color responses. The abscissa gives luminance ratios; the ordinate, the change from Illuminant A in red-green and yellow-blue responses. Red-green responses for each inducing color are plotted at the left; yellow-blue responses are at the right. R-G and Y-B for Illuminant A are assumed to be zero. s Judd’s method of predicting the induced colors utilizes a “neutral” point, calculated from the chromaticity values of the total field, which would be different for the various inducing colors. The distance from the inducing color to the neutral point is used to predict the amount of color induced (JUDD, 1940, 1960). An empirical determination of the neutral point was made for the conditions of this experiment. The chromaticity values of the point that looked white did change with the inducing color, lying on the green side of Illuminant A for the green-inducing color and on the red side for the red. The amount of change, however, was slight, particularly for the red and yellow, and would not influence the predicted chromaticities. 3 Values are calculated assuming that the eye is completely adapted to Illuminant A; the red-green and blue-yellow responses to Illuminant A are thus both zero. This is comparable to the analysis of JAMESOW and HURVICH (1961) but is probably an over-simpli~~ation, as they would no doubt agree, since Ill~inant A never appears completely white.
510
Jo ANN
S. KINNI.~
chromatic response values for red-green and yellow-blue. For example, the green-inducing color has the largest green component (-0629 R-G) and it induced the most red, while the yellow has the smallest red component (+0.078 R-G) and induced the least green. Differences in the Y-B responses are less both for the inducing and induced colors. Figure 14 shows the data plotted in the color specification system of HURVICH and JAMESON(1956). In this presentation, equal angles represent equal hue steps, while equal distances from the center are equal saturation steps. Illuminant A is represented by the center of the circle and the inducing colors by the solid triangles. The data points for the induced colors move out from the center, away from the inducing color, in an orderly progression as the luminance ratio is increased.
‘,
‘\,$ /
FIG.
/
‘,
:,
,,
\ -0.1
,,
14. The color specification system of Hurvich and Jameson.
Data points are colors induced by various luminance ratios of the inducing colors.
A comparison of the data from this experiment with mathematical predictions derived from various theories is beyond the scope of this paper. However, the author would like to point out the conceptual advantage of the polar plot of Hurvich and Jameson in the ease with which the color relations can be visualized. This ease of con~eptua~zation should be a factor in evaluating the utility of a system. Various theories have been proposed to account for color contrast, but modern versions of them differ mainly in the terminology used rather than basic conceptions. Agreement is widespread that there is a physiological basis for contrast rather than the error of judgment
Factors Affecting induced Color
521
that Helmholtz proposed. 4 The fundamental principle in many modern theories is that retinal areas adjacent to, but not directly stimulated by, the surround color show decreased sensitivity to the wavelengths of the surround color and increased sensitivity to the other wavelengths. At the physiolo~cal level, this change in sensitivity could be decreased response to the stimulating wavelengths (SELF, 1959; FLOCKS, 1960), through adaptation, or increased response to remaining wavelengths through opponent activity (HURVICH and JAMESON,1961) or both, Since the net result is the same, these data on the appearance of the colors cannot be used to support one or the other interpretation. For example, it has been shown here that the induced color changes from that of Illuminant A toward that of the complement of the inducing color as the luminance of the inducing color is increased relative to that of the induced. This phenomenon may be viewed as a case of increasing adaptation to the inducing wavelengths and the consequent depression of responsiveness to these components in the response to Illuminant A. On the other hand, the phenomenon may be viewed as a case of greater opponent activity induced into the focal area, thereby changing its appearance. The older argument, that the instantaneous appearance of color contrast contradicted the adaptation theory, has been discarded due to the results on rapid adaptation times (SCHOUTENand ORNSTBIN,1939). Therefore, no attempt was made in this investigation to retain a division between simultaneous and rapid successive contrast. Nevertheless, it was observed casually that there appeared to be temporal differences among the inducing colors and perhaps an investigation of these factors might help differen~ate between the two physiological theories. SUMMARY An experimental investigation of the factors affecting induced color was made by having observers compare the color induced into a field of Ill~nant A with another field of actual colored light. Four inducing colors, red, yellow, green and blue, were studied; these colors were varied in size, purity and luminance ratio to the induced field. Results are given both in terms of the C.I.E. values of the comparison field that yielded the same color as the induced color, and in terms of the luminance of the comparison field required to match the induced field in brightness, The amount of color induced increased as the size, lu~nan~ ratio, and, to a lesser extent, the purity of the inducing color were increased. The brightness of the induced color decreased with increasing luminance ratio. The effects of single parameters were found to be cumulative.
*JUDD (1960) attempts to retain HELMHOLTZ’S explanation (1924)by rephrasing it to include a discounting of the illumination on the scene, the discounted value being some kind of average of the total colors received from the scene. Since this explanation is on a conceptual rather than a physiological level, it is not included here.
.lo ANN S. KINN~\
522
APPENDIX C.I.E.
VALUES OF INI)UCED COLOR
Inducing Color-Green
(Wratten #60i-65A)x
Size
Luminance Ratio (Inducing~Induc~d} 0 --_~___
Purity
l/2 X
MS
__MC
---JK
___-FD
~-
__.?
s
1.2/l
2/l
__
P O-3602 0.3736 0.3853
z
.r
Y
0.1621 0.1553 O-1494
0*4817
0.3521
01662
0.3861 I+3883 0.3952
01014 0.1037 0*1109
0.5565
0.3646
00788
0.3752 0.3907 O-3948
0.1107 o-1 192 0.1215
0.5428
0.3567
0.1005
z
all color A+color 5A -t color
0.4621
?’ 0.3918
all color A -t color 5A + color
0.4773
0.4033
0.1194
all color A + color SA + color
0.4751
04003
0.1246
~_. 0.4857
04093
0.1050
0.5293 0.5121 0.4995
0.3919 0.4038 o-4064
0.0788 0.0841 0.0941
0.5405
0.3725
00870
0.4750
0.4012
0.1238
0.5084 0.4953 0.4856
0.3784 0.3891 0.3954
O-1132 0.1156 0.1190
0.5304
03615
0.1081
all color A + color 5A + color
Mean of 4 O’s all color A -_I-color 5A -i- color
01461
0.4777 0.4711 0.4653 0.5125 0*5081 0.4939 _^0.5142 0.4901 0.4837
Inducing Color-Blue
(Wratten #44A)-4”
--
-
-____
Size
Luminance Ratio (Inducing/Induced) 0 -
Purity
MS
all color A + color 5A + color
MC
112
1.2/l
2/l
X 0.4750
Y 0.4105
X
0.5075 0.5091 0.4883
Y 04085 0.4223 0.4097
2
01144
@0840 @0686 0*1020
0.5242
Y 04075
0.0683
all color A + color 5A + color
0.4744
o-4106
0.1151
0.5082 0.5140 0.5010
04085 04081 04089
0.0833 0.0779 0.0900
0.5272
0.4073
0.0655
JK
all color A + color 5A + color
0.4757
0*4105
0.1138
O-5126 O-5053 0.4954
04082 04087 0.4093
0.0792 0.0860 o-0954
0.5413
0.4064
PO523
FD
all color A + color 5A + color
0.4840
04051
0.1109
0.5347 0.3947 0.5242 04075 0.5050 0.4348 --__
0*0706 00683 0.0602
0.5550
0.3906
0.0544
0.4773
04092
0.1135
0.5157 0.5132 o-4974
0.0793 0.0752 0*0869
0.5369
0.4030
00601
Mean of 4 O’s all color A _t color 5A -t color
2
X
04050 O-4116 0.4157
z
Factors Aikting Inducing Color-Yellow
523
Induced Color (Wratten # 16)--4”
size
Luminance Ratio (Inducing/Induced) 1.2/l
0
Purity
Z
x
Y
Z
MS
All color A f color 5A + color
0.4284
04085
01631
04150 0.4284 0.4194
04058 04085 04067
0.1792 0.1631 0.1739
0.3816
0.3762
0.2422
MC
all color A + color 5A + color
0.4374
0.4104
0.1522
0.4261 0.4261 04150
04081 0.4081 0.4058
0.1658 0.1658 0.1792
0.3720
0.3532
0.2748
JK
all color A + color 5A -k color
04418
0.4113
0.1468
04261 0.4150 0.3928
0.4081 0.4058 04012
0.1658 0.1792 0.2060
0.3833
0.3860
0.2307
FD
all color A + color 5A + color
0.4374
0.4104
01522
0.3955 04004 @4294
0.3916 04043 0.4335
0.2129 0.1953 0.1371
0.3883
0.3882
0.2235
0.4362
0.4102
0.1536
0.4157 04175 0.4142
04034 04067 0.4118
0.1809 0.1758 0.1741
0.3813
0.3759
0.2428
l/2
Y
X
Mean of 4 O’s all color A + color 5A + color
X
Z
Inducing Color-Red
Y
(Wratten #33)--4”
2/l
Size
Luminance Ratio (Inducing/Induced) 1*2/l
0
Purity X
Y
Z
X
Y
z
X
Y
z
MS
all color A + color 5A -t color
0.4334
0.4272
0.1394
0.4126 0.4205 0.4288
04405 0.4355 0.4302
0.1469 0.1440 0.1411
0.4012
04478
0.1510
MC
all color A + color 5A + color
0.4500
0.4160
0.1340
0.4365 0.4298 0.4269
0.4366 04467 0.4510
0.1268 0.1235 0.1220
0.4287
04484
0.1229
JK
all color A + color 5A + color
0.4365
04366
0.1268
0.4227 0.4196 0.4152
0.4573 O-4620 0.4686
0.1200 0.1184 0.1162
0.3693
0.5373
0.0933
FD
all color A + color 5A + color
0.4334
04272
0.1394
0.4177 0.4152 04425
0.4648 0.4686 0.4851
0.1175 0.1162 0.0724
0.3956
0.4979
0.1065
0.4383
0.4268
0.1349
0.4224 0.4213 0.4284
04498 0.4532 0.4587
0.1278 0.1255 01129
0.3987
0.4829
0.1184
Mean of 4 O’s all color A + color 5A + color
l/2
2/l
KK
Jo ANN
524
S. KINNEY
Values for various sizes of Inducing Field-Purity Inducing Filter
5A i- color; Luminance ratio 1.2/l
Size 3” 4’ _~______~~__~_________._.-_..__---_-
0 X
Z
s
0.1138 0.1066 0.1053 0.0974
42 ’ -. Z
X
0.4883 0.5010 04954 0.5050
Y 0.4097 0.4089 0.4093 0.4348
0.1020 0.0900 0.0954 0.0602
Z
MS MC JK FD
0.4757 0.4834 0.4848 0.4786
Y 0.4105 0.4100 04099 0.4239
60 + 65A MS MC JK FD
0.4621 0.4804 0.4653 0.4715
0.3918 0.3969 0.3853 0.4122
0.1461 0.1226 0.1494 0.1163
0.4653 0.4939 0.4837 0.4995
0.3853 0.3952 0.3948 0.4064
0.1494 0.1109 0.1215 0.0941
0.4721 0.5032 0.5174 0.5267
0.3715 0.3823 0.3730 0.3671
0.1564 0.1146 0.1095 0.1062
16
MS MC JK FD
0.4261 0.4351 0.4261 0.4322
04081 0.4099 04081 0.4343
0.1658 0.1550 0.1658 0.1335
0.4194 0.4150 0.3928 0.4294
0.4067 0.4058 0.4012 0.4335
0.1739 0.1792 0.2060 0.1371
0.3928 0.4061 0.3708 04061
0.4012 0.4039 0.3966 0.4039
0.2060 0.1900 0.2326 0.1900
33
MS MC JK FD
0.4551 04442 0.4374 0.4312
0.4127 0.4200 0.4241 0.4288
0.1322 0.1358 0.1385 0.1400
0.4288 0.4269 0.4152 04425
0.4302 0.4510 0.4686 0.4851 -----
0.1411 0.1220 0.1162 0.0724
0.3970 0.3823 0.3417 0.3960
0.4505 0.5179 0.5787 0.5793
0.1525 0.0998 0.0796 0.0247
Mean of 4 observers 44A 0.4806 60 + 65A 0.4698 16 0.4299 33 04420
0.4136 0.3966 0.4151 0.4214
0.1058 0.1336 0.1550 0.1366
0.4974 0.4856 0.4142 0.4284
0.4157 0.3954 0.4118 0.4587
0.0869 0.1190 0.1741 0.1129
0.5260 0.5048 0.3940 0.3792
0.4173 0.3735 0.4014 0.5316
0.0567 0.1217 0.2046 0.0892
44A
Values for Maximum Color induced-Size: Inducing Filter
4;E”; Purity: All color;
X
Y
z
MS MC JK FTI
0.5316 0.5978 06095 0.5943
0.4070 0.4014 0.3900 0.3235
0.0614 OWO8 OWO6 0.0823
60 + 65A MS MC JK FD
0.4963 0.5866 0.5708 0.5990
0.3225 0.3500 0.3386 0.3204
0.1812 0.0634 0.0906 0.0806
16
MS MC JK FD
0.3519 0.3386 0.3192 0.3482
0.3544 0.3279 0.3336 0.3697
0.2937 0.3335 0.3472 0.2821
33
MS MC JK FD
0.3180 0.2776 0.2776 0.3307
0.5011 0.6748 0.6748 0.5953 ~____.
0.1809 0.0476 0.0476 0.0740
44A
______~ 44A 60 + 65A 16 33
0
0.5833 0.5632 0.3395 0.3010
Mean 0.3805 0.3329 0.3464 0.6115
0.0363 0.1039 0.3141 0.0875
0.5097 0.5338 0.5272 0.5335
Y 0.4084 04069 04073 0.4465
0.0820 0.0593 0.0655 0.0201
Luminance ratio: 2/l
Factors Affecting Induced Color
525
REFERENCES BOYNTON,R. M. (1960). Theory of color vision. J. opf. Sot. Amer. 50, 929-944. DIAMOND, A. L. (1953). Fovea1 simultaneous brightness contrast as a function of inducing- and test-field luminances. J. exp. Psychol. 45, 304-314. EVANS, R. M. (1943). Visual processes and color photography. J. opt. Sot. Amer. 33, 579-614. FLOCKS, M. (1960). The physiologic basis of simultaneous color contrast. Trans. Pucif: Cst oto-ophthal. Sot. 41, 153-177. HEINEMANN, E. G. (1955). Simultaneous brightness induction as a function of inducing- and test-field luminances. J. exp. Psychol. 50, 89-96. v. HELMHOLTZ,H. (1924). Treatise on Physiological Optics, Vol. II, pp. 264-301. (Translated from the third German Edition by J. P. C. SOUTHALL.) Optical Society of America. HELSON, H. and SELF, C. (1961). A study ofcoloured shadows. Maxwell Colour Centenary, London. HESS, C. and PRETORI, H. (1894). Messende Untersuchungen iiber die Gesetzmlssigkeit des simultanen Helligkeitscontrastes, v. Gruefes Arch. Ophthal. 40, l-24. HURVICH, L. M. and JAMESON, D. (1956). Some quantitative aspects of an opponent-colors theory. IV. A Psychological color specification system. J. opt. Sot. Amer. 46, 416-421. JAMESON,D. and HURVICH, L. M. (1959). Perceived color and its dependence on focal, surrounding, and preceding stimulus variables. J. opt. Sot. Amer. 49, 890-898. JAMESON,D. and HURVICH, L. M. (1961). Opponent chromatic induction: experimental evaluation and theoretical account. J. opt. Sot. Amer. 51, 46-53. JUDD, D. B. (1935). A Maxwell triangle yielding uniform chromaticity scales. J. opt. Sot. Amer. 25, 24-35. JUDD, D. B. (1940). Hue saturation and lightness of surface colors with chromatic illumination. J. opt. Sot. Amer. 30, 2-32. JUDD, D. B. (1960). Appraisal of Land’s work on two-primary projections. J. opt. Sot. Amer. 50,254-268. KARP, A. (1959). Colour-image synthesis with two unorthodox primaries. Nature, Lond. 184, 710-712. KIRSCHMANN, A. (1890). Uber die quantitativen Verhlltnisse des simultanen Helligkeits- und FarbenContrastes. Psycho/. Stud. (W&t), 6, 417491. LAND, E. H. (1959a). Color vision and the natural image. Part I. Proc. nat. Acud. Sci., Wash., 45, 115-129. LAND, E. H. (1959b). Color vision and the natural image. Part II. Proc. nut. Acud. Sci., Wash., 45,636644. SCHOUTEN,J. F. and ORNSTEIN, L. S. (1939). Measurements on direct and indirect adaptation by means of a binocular method. J. opt. Sot. Amer. 29, 168-182. SELF, H. C. (1959). A quantitative study of colored shadows. Ph.D. dissertation, University of Texas, Austin, Texas. WALLS, G. L. (1960). Land! Land! Psycho/. Bull. 57, 2948. WILSON, M. H. and BROCKLEBANK,R. W. (1960). Two-colour projection phenomena. J. photogr. Sci. 8, 142-150. WOODWORTH, R. S. (1938). Experimental Psychology, pp. 567-571. Henry Holt and Co., New York.