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Matching display resolution and addressability to human visual capacity
Matching display resolution and addressability to human visual capacity GERALD M MURCH AND ROBERT J BEATON
The perceived image quality of a digital display is affected by two independent system characteristics, namely resolution and addressability. This p a p e r discusses a quantitative procedure for selecting optimal levels of resolution and addressability based upon the performance constraints of human vision.
Keywords: digital display image quality, resolution, addressability
In an earlier paper, a metric was introduced that could be used to relate CRT display resolution and addressability 1. Although a general approach to the use of the metric was described, no specific method was developed for assessing whether a given display was optimized in terms of resolution and addressability. In the present article, such an extension of the earlier work is introduced: the metric known as the resolution/addressability ratio (RAR) is reviewed and a means by which an RAR can be evaluated is presented. For a visual display unit to be used comfortably and efficiently, the image must be constituted in light of the imaging requirements of the human visual system. In digital display systems employing a cathode ray tube (CRT), the critical attributes are resolution and addressability. By matching these two characteristics of the display to the imaging limits of vision, an optimized system may be obtained. In essence, resolution is a property of the design of the display device. It is derived from the width of a line or spot imaged on the screen: the narrower the line or the smaller the spot, the higher the resolution. From the measured line width, various measures of resolution can be derived, such as lines per unit distance, modulation transfer function (MTF) and spot width at certain percentages of peak luminance. In the application presented here, the line width at 50% of the maximum
Tektronix Laboratories, Tektronix Inc., PO Box 500, MS 50-320, Beaverton, OR 97077, USA DISPLAYS,JANUARY 1 9 8 8
luminance intensity is used because, for monochrome CRT displays, a Gaussian model provides an excellent empirical description of the line (pixel) profile and simple conversion factors exist to translate into other metrics of resolution 2"a. It should be appreciated, however that some display systems possess non-Gaussian line (pixel) profiles and that the required quantitative analyses are beyond the scope of this paper 3'4. Addressability is a characteristic of the display controller and represents the ability to select and activate a unique line (pixel) on the screen. For rastered displays, addressability is defined in terms of the number of discrete lines (pixels) per unit distance on the display screen (e.g. 480 lines per picture height, 100 pixels per unit distance). With this definition, the arithmetic inverse of addressability denotes the centre-to-centre distance between adjacent display picture elements, either along or across a raster scan line. Since addressability is controlled by the hardware driving the CRT, and since resolution is determined by the design of the CRT, these two display characteristics are independent of one another. However, to obtain high levels of image quality, certain relations need to be maintained between resolution and addressability. For example, if resolution is too low (large spot sizes), successive lines will over-write preceding lines. Under some conditions, this may produce image artifacts such as false contours. Conversely, if address.ability is too low (large spot separations), then adjacent raster lines will not merge and they will appear as visible stripes.
0141--9382/88/010023~ $03.00© 1988Butterworth&Co (Publishers)Ltd
23
RELATING RESOLUTION A N D ADDRESSABILITY A primary goal in engineering a visual display system is to attain sufficient image quality to maximize the transfer of 'information' from the display screen to the human operator. Although numerous factors contribute to overall image quality, resolution and addressability directly impact two fundamental criteria underlying this design goal. Furthermore, these two aspects of a display system are under the control of the display-system designer. Other aspects influencing image quality are under the control of the system user and include the amount and type of ambient illumination, the formatting of information on the screen, and so on. The first criterion, which the authors have termed the adjacent raster line (pixel) requirement, states that the raster structure of a display must be imperceptible to an operator located at a typical (46 cm) viewing distance. This requirement is intended to eliminate visible 'noise', which arises from the discrete picture elements of digital display systems and which bears no relevant information for the operator. Display systems that meet the adjacent raster line (pixel) criterion present uniformly bright solid-filled areas and alphanumeric characters, which appear continuously constructed and highly legible. Failing to meet this criterion will lead to visible raster modulation which, in turn, has a detrimental effect on operator performance, such as reading speed s, visual search ~ and threshold detection of information component 7. The second image-quality criterion, termed the alternate raster line (pixel) requirement, states that individual lines (pixels) within an alternating on-off-on-off pattern must be visible to an operator from a typical viewing distance. This requirement optimizes the visibility of high spatial frequency components, such as narrow lines and fine details within an image. For a CRT system with a smoothly decreasing MTF, optimizing the alternate raster line (pixel) criterion also optimizes the information transfer of low spatial frequency components 8. The two image-quality criteria mentioned above place opposing demands upon the optimal specification of display resolution and addressability. For example, increases in display addressability favour the adjacent raster line (pixel) criterion since the modulation (luminance contrast) between adjoining raster lines is reduced; however, this same reduction in modulation also reduces the detectability of individual lines within an on-off-on-off pattern, thereby disfavouring the alternate raster line (pixel) criterion. Similarly, an increase in resolution favours the alternate raster line criterion as a smaller spot will increase the modulation between pixels. Again, however, this may also render the raster structure visible ~,hen all pixels are active.
RESOLUTION/ADDRESSABILITYRATIO To assess whether or not a display system satisfies the two image-quality criteria mentioned above, the system designer must determine the modulation between adjacent and alternate raster lines (pixels). These 24
1.0 0.8-
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1 % 1
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Figure 1. Adjacent (11) and alternate ( A ) raster line (pixel) modulation as a function of RAR modulation values must then be evaluated in terms of human visual sensitivities to modulation at specific spatial frequencies. It is desired that the modulation between adjacent raster lines (pixels) be below a minimum level required for visual stimulation, while the modulation between alternate raster lines (pixels) should exceed this minimum visual stimulation level. To evaluate display systems over a wide range of resolution and addressability, the authors have employed an oft-discussed metric based upon the geometry of sampled displays9'1°, termed the resolution/ addressability ratio (RAR), given as RAR-
W S
(1)
where W denotes the full width of a raster line (pixel) profile at one-half its maximum luminance intensity and S denotes the peak-to-peak separation between adjacent raster lines (pixels). For example, a 48 cm diagonal display with a height of 27.5 cm and an addressability of 1 024 lines has a peak-to-peak separation of 27.5/1 024 = 0.27 mm/line. Assuming a 0.38 mm wide spot profile, the resulting R A R value is 1.41. By using a numerical simulation program, modulation values for adjacent and alternate raster lines (pixels) were determined under various combinations of resolution and addressability and, hence, R A R values. For each R A R value, the stimulation program constructed a waveform that represented the luminance pattern across several raster lines (pixels). These calculations were performed by convolving a Gaussian spot profile having a specific width (I4') with a series of unit delta functions spaced at a specific separation (S). The modulation values, determined by Fourier analysis of the resulting periodic raster (pixel) structure, are plotted in Figure 1. The observed trend in modulation, over a range of R A R values from 0.35 to 2.4, can be described by M = 2 e x p [ 3 . 6 ( R A R ) - 7 . 0 ( R A R ) z + ( R A R ) 3]
(2)
where M denotes modulation and R A R is defined by equation (1). As an example, for a display with a resolution of 0.38 mm and an addressability of 480 lines within a 27.5 cm vertical display area, the modulation between adjacent raster lines (pixels) is 0.43. With equations (1) and (2), the alternate raster line DISPLAYS, JANUARY 1988
1.0
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70
Figure 2. Human contrast sensitivity function with 90% population limits (broken lines) (pixel) modulation can be computed easily by doubling the separation value used in the corresponding adjacent raster line (pixel) calculation; that is, the RAR value for the alternate criterion is equal to one-half of the RAR value for the adjacent criterion. Example calculations are shown in Figure 1.
SELECTING A N O P T I M A L A N D ADDRESSABILITY
RESOLUTION
The final step in the evaluation procedure is to assess the detectability of adjacent and alternate raster line (pixel) modulation by a human operator. A great deal of visual research has focused on this problem 11. These studies have measured the minimum modulation needed by the visual system to detect a sine-wave pattern of a given spatial frequency. The resultant function, known as the contrast sensitivity function (CSF), provides a direct indication of the human visual system's capability to perceive the modulation between pixels on a raster display. Figure 2 presents the 90% population CSF for sine-wave patterns subtending at least 5 degrees of visual angle and having an average luminance of 10 cd m -2 (ref. 10). This CSF curve is described by the following least-squares regression equation: M--- bo exp[bl((o) + b2(c0)2 + b3(o0)4]
(3)
where M denotes the modulation required for detection at spatial frequency to, expressed in cycles per degree of visual angle. Values for the regression coefficients bo, bl, b2 and ba are 1.7062 x 10 -3, 201.6188 x 10 -3, -2.3161 x 10 -3 and 0.2000 x 10-6, respectively. Equation (3) can be used in conjunction with equation (2) to determine the visibility of adjacent and alternate raster line modulation. Before proceeding, however, it is necessary to determine the spatial frequency, in cycles per degree of visual angle, corresponding to the adjacent and alternate raster lines (pixels) and to rewrite equation (3) in a form that can be used directly with equation (2). For each image-quality criterion, spatial frequency is related to the separation between the raster lines (pixels) under consideration, since peak-to-peak separation DISPLAYS,JANUARY1988
0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 Resolution Addressability Ratio Figure 3. Modulation and visual contrast sensitivity values for the adjacent ( I ) and alternate ( A ) raster line (pixels) criteria: resolution = 0.254 mm equals one period of the waveform cycle. Therefore, using the fact that S = W/RAR [see equation (1)], a separation value can be converted into cycles per degree of visual angle by = ~
= l-~
(4)
where D denotes the viewing distance of the operator from the display screen and S, W and RAR are defined by equation (1). The right-hand side of equation (4) can be substituted into equation (3) to express the CSF as a function of RAR for various levels of display resolution. Figure 3 presents an example of the display evaluation procedure, where a resolution level was chosen and an optimal display addressability was desired. By the use of equation (2), the adjacent and alternate raster line (pixel) modulations were computed for various addressabilities and, therefore, various RAR values, as shown by the two decelerating curves. Next, equations (3) and (4) were used to determine the CSF values for the adjacent and alternate raster line (pixel) criteria, as shown by the two accelerating curves. One bound on the optimal addressability is provided by the intersection of the adjacent raster line (pixel) modulation curve with the corresponding CSF curve, while another bound is provided by the intersection between the two curves for the alternate raster line (pixel) criterion. For a selected resolution level, a range of addressabilities will satisfy the adjacent and alternate raster line (pixel) criteria. In these situations, it will be convenient to choose the adjacent RAR limit since the resulting addressability maximizes the visibility of high spatial frequency components while maintaining the raster modulation at a 'just detectable' level. Table 1 lists the RAR limits for various frequently used resolution levels. Note that the alternate raster line (pixel) limit is twice as large as the corresponding adjacent raster line (pixel) limit.
REFERENCES 1. Mureh, G, Virgin, L and Beaton, R J 'Resolution and addressability: how much is enough' Proc. Soc. Inf. Disp. Vol 26, No 4 (1985) pp 305-308 25
Table 1. Adjacent and alternate raster line (pixel) limits Resolution mm Adjacent limit
0.127 0.254 0.381 0. 508 0.635 0.762
0.71 0.92 1.02 1.09 1.12 1.18
Alternate limit
1.42 1.84 2.04 2.18 2.24 2.36
2. Sherr, S Electronic Displays Wiley, New York (1980) 3. Keller, P A 'A survey of data-display CRT resolution measurement techniques' Soc. Inf. Disp. Seminar Lecture Notes Society for Information Display, Los Angeles (1984) pp 2.2a-l-2.2a-28 4. Infante, C 'CRT technology: progress and issues' Proc. Soc. Inf. Disp. Vol 27, No 4 (1986) pp 245-248 5. Snyder, H L and Maddox, M E Information transfer from computer-generated dot-matrix displays Virginia Polytechnic Institute and State University Technical Report HFL-78-3/ARO-78-1, Blacksburg, VA (October 1978) 6. Snyder, H L, Beamon, W S, Gutmann, J C and
26
Dumker, E D An evaluation of the effects of spot wobble upon observer performance with raster scan displays USAF Report AMRL-TR-79-91, WrightPatterson AFB, OH (January 1980)
7. Keesee, R L Prediction of modulation detectability thresholds for line-scan displays USAF Report AMRL-TR-76-38, Wright-Patterson AFB, OH (December 1976) 8. Beaton, R J .4 human performance based evaluation of quality metrics for hard-copy and soft-copy digital imaging systems Unpublished doctoral dissertation, Virginia Polytechnic Institute and State University, Blacksburg, VA (1984) 9. Sehade, O H 'Image reproduction by a line raster process in Biberman, L M (Ed.) Perception of displayed information Plenum Press, New York (1973) 10. Snyder, H L Human visualperformance andflat panel display image quality Virginia Polytechnic Institute and State University, Human Factors Laboratory, Technical Report HFL-80-1/ONR-80-1, Blacksburg, VA (1980) 11. Kaufman, L Sight and Mind Oxford Press, New York (1974)
DISPLAYS, JANUARY 1988
The perceived image quality of a digital display is affected by two independent system characteristics, namely resolution and addressability. This p a p e r discusses a quantitative procedure for selecting optimal levels of resolution and addressability based upon the performance constraints of human vision.
Keywords: digital display image quality, resolution, addressability
In an earlier paper, a metric was introduced that could be used to relate CRT display resolution and addressability 1. Although a general approach to the use of the metric was described, no specific method was developed for assessing whether a given display was optimized in terms of resolution and addressability. In the present article, such an extension of the earlier work is introduced: the metric known as the resolution/addressability ratio (RAR) is reviewed and a means by which an RAR can be evaluated is presented. For a visual display unit to be used comfortably and efficiently, the image must be constituted in light of the imaging requirements of the human visual system. In digital display systems employing a cathode ray tube (CRT), the critical attributes are resolution and addressability. By matching these two characteristics of the display to the imaging limits of vision, an optimized system may be obtained. In essence, resolution is a property of the design of the display device. It is derived from the width of a line or spot imaged on the screen: the narrower the line or the smaller the spot, the higher the resolution. From the measured line width, various measures of resolution can be derived, such as lines per unit distance, modulation transfer function (MTF) and spot width at certain percentages of peak luminance. In the application presented here, the line width at 50% of the maximum
Tektronix Laboratories, Tektronix Inc., PO Box 500, MS 50-320, Beaverton, OR 97077, USA DISPLAYS,JANUARY 1 9 8 8
luminance intensity is used because, for monochrome CRT displays, a Gaussian model provides an excellent empirical description of the line (pixel) profile and simple conversion factors exist to translate into other metrics of resolution 2"a. It should be appreciated, however that some display systems possess non-Gaussian line (pixel) profiles and that the required quantitative analyses are beyond the scope of this paper 3'4. Addressability is a characteristic of the display controller and represents the ability to select and activate a unique line (pixel) on the screen. For rastered displays, addressability is defined in terms of the number of discrete lines (pixels) per unit distance on the display screen (e.g. 480 lines per picture height, 100 pixels per unit distance). With this definition, the arithmetic inverse of addressability denotes the centre-to-centre distance between adjacent display picture elements, either along or across a raster scan line. Since addressability is controlled by the hardware driving the CRT, and since resolution is determined by the design of the CRT, these two display characteristics are independent of one another. However, to obtain high levels of image quality, certain relations need to be maintained between resolution and addressability. For example, if resolution is too low (large spot sizes), successive lines will over-write preceding lines. Under some conditions, this may produce image artifacts such as false contours. Conversely, if address.ability is too low (large spot separations), then adjacent raster lines will not merge and they will appear as visible stripes.
0141--9382/88/010023~ $03.00© 1988Butterworth&Co (Publishers)Ltd
23
RELATING RESOLUTION A N D ADDRESSABILITY A primary goal in engineering a visual display system is to attain sufficient image quality to maximize the transfer of 'information' from the display screen to the human operator. Although numerous factors contribute to overall image quality, resolution and addressability directly impact two fundamental criteria underlying this design goal. Furthermore, these two aspects of a display system are under the control of the display-system designer. Other aspects influencing image quality are under the control of the system user and include the amount and type of ambient illumination, the formatting of information on the screen, and so on. The first criterion, which the authors have termed the adjacent raster line (pixel) requirement, states that the raster structure of a display must be imperceptible to an operator located at a typical (46 cm) viewing distance. This requirement is intended to eliminate visible 'noise', which arises from the discrete picture elements of digital display systems and which bears no relevant information for the operator. Display systems that meet the adjacent raster line (pixel) criterion present uniformly bright solid-filled areas and alphanumeric characters, which appear continuously constructed and highly legible. Failing to meet this criterion will lead to visible raster modulation which, in turn, has a detrimental effect on operator performance, such as reading speed s, visual search ~ and threshold detection of information component 7. The second image-quality criterion, termed the alternate raster line (pixel) requirement, states that individual lines (pixels) within an alternating on-off-on-off pattern must be visible to an operator from a typical viewing distance. This requirement optimizes the visibility of high spatial frequency components, such as narrow lines and fine details within an image. For a CRT system with a smoothly decreasing MTF, optimizing the alternate raster line (pixel) criterion also optimizes the information transfer of low spatial frequency components 8. The two image-quality criteria mentioned above place opposing demands upon the optimal specification of display resolution and addressability. For example, increases in display addressability favour the adjacent raster line (pixel) criterion since the modulation (luminance contrast) between adjoining raster lines is reduced; however, this same reduction in modulation also reduces the detectability of individual lines within an on-off-on-off pattern, thereby disfavouring the alternate raster line (pixel) criterion. Similarly, an increase in resolution favours the alternate raster line criterion as a smaller spot will increase the modulation between pixels. Again, however, this may also render the raster structure visible ~,hen all pixels are active.
RESOLUTION/ADDRESSABILITYRATIO To assess whether or not a display system satisfies the two image-quality criteria mentioned above, the system designer must determine the modulation between adjacent and alternate raster lines (pixels). These 24
1.0 0.8-
~
1 % 1
I
I
[
I
I
I
~
•.,= 0.6 --~ = •"o 04
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Alternate "~p,xel
-
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0.0
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I
I
0.4
0.6
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-
--
1.2
1.4
-
1.6
Resolution/Addressability
,
1.8
-
[
2.0
2,2
2.4
Ratio
Figure 1. Adjacent (11) and alternate ( A ) raster line (pixel) modulation as a function of RAR modulation values must then be evaluated in terms of human visual sensitivities to modulation at specific spatial frequencies. It is desired that the modulation between adjacent raster lines (pixels) be below a minimum level required for visual stimulation, while the modulation between alternate raster lines (pixels) should exceed this minimum visual stimulation level. To evaluate display systems over a wide range of resolution and addressability, the authors have employed an oft-discussed metric based upon the geometry of sampled displays9'1°, termed the resolution/ addressability ratio (RAR), given as RAR-
W S
(1)
where W denotes the full width of a raster line (pixel) profile at one-half its maximum luminance intensity and S denotes the peak-to-peak separation between adjacent raster lines (pixels). For example, a 48 cm diagonal display with a height of 27.5 cm and an addressability of 1 024 lines has a peak-to-peak separation of 27.5/1 024 = 0.27 mm/line. Assuming a 0.38 mm wide spot profile, the resulting R A R value is 1.41. By using a numerical simulation program, modulation values for adjacent and alternate raster lines (pixels) were determined under various combinations of resolution and addressability and, hence, R A R values. For each R A R value, the stimulation program constructed a waveform that represented the luminance pattern across several raster lines (pixels). These calculations were performed by convolving a Gaussian spot profile having a specific width (I4') with a series of unit delta functions spaced at a specific separation (S). The modulation values, determined by Fourier analysis of the resulting periodic raster (pixel) structure, are plotted in Figure 1. The observed trend in modulation, over a range of R A R values from 0.35 to 2.4, can be described by M = 2 e x p [ 3 . 6 ( R A R ) - 7 . 0 ( R A R ) z + ( R A R ) 3]
(2)
where M denotes modulation and R A R is defined by equation (1). As an example, for a display with a resolution of 0.38 mm and an addressability of 480 lines within a 27.5 cm vertical display area, the modulation between adjacent raster lines (pixels) is 0.43. With equations (1) and (2), the alternate raster line DISPLAYS, JANUARY 1988
1.0
I
I
I
I
I
0.8 .Co 0.6
II//iii
0.2
,0
\ , . q ,
,
,
,
,
,
,
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-
.~0.6 _
Visible ~E 0.4
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~= 0.4 _
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///~,//
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/
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_
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I I 0.0 - - ~ l J / I 0 10 20 30 40 50 60 Spatial frequency (cycles / degrees)
70
Figure 2. Human contrast sensitivity function with 90% population limits (broken lines) (pixel) modulation can be computed easily by doubling the separation value used in the corresponding adjacent raster line (pixel) calculation; that is, the RAR value for the alternate criterion is equal to one-half of the RAR value for the adjacent criterion. Example calculations are shown in Figure 1.
SELECTING A N O P T I M A L A N D ADDRESSABILITY
RESOLUTION
The final step in the evaluation procedure is to assess the detectability of adjacent and alternate raster line (pixel) modulation by a human operator. A great deal of visual research has focused on this problem 11. These studies have measured the minimum modulation needed by the visual system to detect a sine-wave pattern of a given spatial frequency. The resultant function, known as the contrast sensitivity function (CSF), provides a direct indication of the human visual system's capability to perceive the modulation between pixels on a raster display. Figure 2 presents the 90% population CSF for sine-wave patterns subtending at least 5 degrees of visual angle and having an average luminance of 10 cd m -2 (ref. 10). This CSF curve is described by the following least-squares regression equation: M--- bo exp[bl((o) + b2(c0)2 + b3(o0)4]
(3)
where M denotes the modulation required for detection at spatial frequency to, expressed in cycles per degree of visual angle. Values for the regression coefficients bo, bl, b2 and ba are 1.7062 x 10 -3, 201.6188 x 10 -3, -2.3161 x 10 -3 and 0.2000 x 10-6, respectively. Equation (3) can be used in conjunction with equation (2) to determine the visibility of adjacent and alternate raster line modulation. Before proceeding, however, it is necessary to determine the spatial frequency, in cycles per degree of visual angle, corresponding to the adjacent and alternate raster lines (pixels) and to rewrite equation (3) in a form that can be used directly with equation (2). For each image-quality criterion, spatial frequency is related to the separation between the raster lines (pixels) under consideration, since peak-to-peak separation DISPLAYS,JANUARY1988
0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 Resolution Addressability Ratio Figure 3. Modulation and visual contrast sensitivity values for the adjacent ( I ) and alternate ( A ) raster line (pixels) criteria: resolution = 0.254 mm equals one period of the waveform cycle. Therefore, using the fact that S = W/RAR [see equation (1)], a separation value can be converted into cycles per degree of visual angle by = ~
= l-~
(4)
where D denotes the viewing distance of the operator from the display screen and S, W and RAR are defined by equation (1). The right-hand side of equation (4) can be substituted into equation (3) to express the CSF as a function of RAR for various levels of display resolution. Figure 3 presents an example of the display evaluation procedure, where a resolution level was chosen and an optimal display addressability was desired. By the use of equation (2), the adjacent and alternate raster line (pixel) modulations were computed for various addressabilities and, therefore, various RAR values, as shown by the two decelerating curves. Next, equations (3) and (4) were used to determine the CSF values for the adjacent and alternate raster line (pixel) criteria, as shown by the two accelerating curves. One bound on the optimal addressability is provided by the intersection of the adjacent raster line (pixel) modulation curve with the corresponding CSF curve, while another bound is provided by the intersection between the two curves for the alternate raster line (pixel) criterion. For a selected resolution level, a range of addressabilities will satisfy the adjacent and alternate raster line (pixel) criteria. In these situations, it will be convenient to choose the adjacent RAR limit since the resulting addressability maximizes the visibility of high spatial frequency components while maintaining the raster modulation at a 'just detectable' level. Table 1 lists the RAR limits for various frequently used resolution levels. Note that the alternate raster line (pixel) limit is twice as large as the corresponding adjacent raster line (pixel) limit.
REFERENCES 1. Mureh, G, Virgin, L and Beaton, R J 'Resolution and addressability: how much is enough' Proc. Soc. Inf. Disp. Vol 26, No 4 (1985) pp 305-308 25
Table 1. Adjacent and alternate raster line (pixel) limits Resolution mm Adjacent limit
0.127 0.254 0.381 0. 508 0.635 0.762
0.71 0.92 1.02 1.09 1.12 1.18
Alternate limit
1.42 1.84 2.04 2.18 2.24 2.36
2. Sherr, S Electronic Displays Wiley, New York (1980) 3. Keller, P A 'A survey of data-display CRT resolution measurement techniques' Soc. Inf. Disp. Seminar Lecture Notes Society for Information Display, Los Angeles (1984) pp 2.2a-l-2.2a-28 4. Infante, C 'CRT technology: progress and issues' Proc. Soc. Inf. Disp. Vol 27, No 4 (1986) pp 245-248 5. Snyder, H L and Maddox, M E Information transfer from computer-generated dot-matrix displays Virginia Polytechnic Institute and State University Technical Report HFL-78-3/ARO-78-1, Blacksburg, VA (October 1978) 6. Snyder, H L, Beamon, W S, Gutmann, J C and
26
Dumker, E D An evaluation of the effects of spot wobble upon observer performance with raster scan displays USAF Report AMRL-TR-79-91, WrightPatterson AFB, OH (January 1980)
7. Keesee, R L Prediction of modulation detectability thresholds for line-scan displays USAF Report AMRL-TR-76-38, Wright-Patterson AFB, OH (December 1976) 8. Beaton, R J .4 human performance based evaluation of quality metrics for hard-copy and soft-copy digital imaging systems Unpublished doctoral dissertation, Virginia Polytechnic Institute and State University, Blacksburg, VA (1984) 9. Sehade, O H 'Image reproduction by a line raster process in Biberman, L M (Ed.) Perception of displayed information Plenum Press, New York (1973) 10. Snyder, H L Human visualperformance andflat panel display image quality Virginia Polytechnic Institute and State University, Human Factors Laboratory, Technical Report HFL-80-1/ONR-80-1, Blacksburg, VA (1980) 11. Kaufman, L Sight and Mind Oxford Press, New York (1974)
DISPLAYS, JANUARY 1988