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Archival storage of color films by rainbow holographic technique
Volume 27, number 3
OPTICS COMMUNICATIONS
December 1978
ARCHIVAL STORAGE OF COLOR FILMS BY RAINBOW HOLOGRAPHIC TECHNIQUE F.T.S. YU, Anthony TAI and Hsuan CHEN * Electrical and Computer Engineering Department, ICayneState University, Detroit, 114148202, USA
Received 7 August 1978
A technique of generating color holographic imageswith a one-step rainbow holographic process is described. This technique offers the capability of archival storage of color materials on a single black and white photographic film. The process is very simple to implement and it allows the reconstruction of the color image with a white light source. Although some degree of color blur is inherent with the rainbow holographic process, it can be minimized by the proper design of the optical system. A simple experimental result is also presented.
1. In~oducfion In an earlier paper [ 1], we have demonstrated a technique of generating color 3-dimensional images with the one-step rainbow holographic process [ 2 - 4 ] . We have shown that with a fairly simple optical arrangement, one could reconstruct a 3-dimensional image with faithful color reproduction using a black and white film as the recording medium. The reconstructed image was also exceedingly bright under ordinary white light illumination which is due to the convergence nature of the rainbow process [2,5,6]. The major disadvantage of this technique is the limited field of view restricted by the finite aperture of the imaging lens. This may be a serious restriction for the recording of 3-dimensional images. It is, however, relatively unimportant in the recording of 2-dimensional images. This process is, therefore, uniquely suitable for the recording of 2-dimensional color pictures, and in this paper, we shall apply it to the archival storage of color pictures. Archival storage of the finished color films has long been an unresolved problem for the major libraries and fdm industries all around the world. One reason is that the organic dyes used in the color fil.m are usually unstable under prolonged storage. This causes * With the Department of Physics, Saginaw Valley State College, University Center, Michigan 48710,
a gradual fading of the color in the original image. There are several ways to preserve the true color of the Film, but all of them possess certain disadvantages. For example, by the repetitive application of primary color filters, one can preserve the color image on three different rolls of the black of white Films. To reconstruct the original color image, a system with three different primary color projectors must be used for their respective Films. At the same time, the Films must be advanced in perfect unison and the images must be overlapped in perfect precision. Since the colors of the reproduced image are derived from the filtered light sources which are not subjected to fading like the organic dyes, the true colors of the image can be preserved. However, there are two major shortcomings with this method. First, the storage volume for each Film is tripled. Secondly, the reproduction system will be elaborate and expensive. Alternatively, one can use Fourier color holographic technique as was proposed by Ill [7--9], to store each color component into a single triple-exposure hologram. This would greatly reduce the required storage volume of the archives. However, in the reconstruction process of the color image, a system of three critically aligned lasers is required. This technique is therefore not suitable for the use as a direct viewing system for public usage in libraries. Also, there would inadvertently be some cut off of the high spatial frequency signals in the spatial filtering process, causing a marginal loss in resolution. 307
Volume 27, number 3
OPTICS COMMUNICATIONS
In this paper, we shall describe a technique of color image preservation using the one-step rainbow holographic technique that we have developed [2]. It may be the simplest and most efficient technique in use today. As with other color preservation techniques, this holographic process can be used to reproduce color images on a new color photographic film. It also allows the direct viewing of the color hologram images using only a simple white light source for illumination. This capability makes the rainbow holographic technique particularly suitable for library applications.
2. Holographic recording In our earlier paper [1] on the recording of color 3-dimensional images, we made use of an arrangement that would produce orthoscopic images. In the recording of 2-dimensional images, however, it is irrelevant whether the reconstructed images are orthoscopic or pseudoscopic, and we shall make use of an arrangement that produces pseudoscopic'images for our present application because of its greater simplicity and larger field of view [2,3]. The optical arrangement utilized in the construction of the color rainbow hologram is illustrated in fig. 1.
December 1978
A He-Ne laser emitting at wavelength 6328 A and two argon lasers, emitting at wavelengths of 5145 A and 4765 A respectively are used as the illuminating sources. The laser beams are attenuate individually with neutral density f'flters to compensate for the differences in the light intensities of the three laser lights and the spectral responses of the recording medium. The color film strip containing the color images to be recorded is mounted on a film transport and back illuminated by a fine diffuser. The diffusely illuminated color transparency is then imaged by an achromatic imaging lens through a narrow slit onto a plane close to the holographic film which is mounted on a light tight f'tim transport. For simplicity, a collimated reference beam is used in the construction of the holograms. The holographic recordings are then performed in a frame by frame basis with the two film transports advancing synchronously after each recording. The intensities of the three laser lights are adjusted to the appropriate levels such that the corresponding optimal exposure times for the three colors would be the same. Thus the photographic film is exposured to the three laser beams simultaneously through a single exposure. After the recording film is developed, a series of color rainbow holograms are formed on the film strip.
3. Image reconstruction M
BS
8S
BS
Io Fig. 1. Optical arrangement for hologram construction: M, mirror; BS, beam splitter; SHR, shutter; ND, neutral density filter; SF, spatial filter; CL, achromatic collimating lens; IML, achromatic imaging lens; O, object color transparency; IO, image of object; H, holographic film.
308
A collimated white light illuminating at the conjugate reference angle is used in the reconstruction. We found that the best result is obtained by using an optical system which is symmetric to that utilized in the holographic recording, as illustrated in fig. 2. When illuminated by the conjugate collimated white light, each of the three holograms formed by the different laser sources will be diffracted into continuous spectral bands of images. However, only the appropriate wavelengths would be able to propagate through the narrow slit and reconstruct the color hologram image at the output plane. We note that if a symmetric system is used in the construction and the reconstruction of the hologram, the light diffracted by the hologram would simply retrace the light path of the holographic recording process and produce the original image. We see that any aberration that may exist in the optical components would be automatically compensated. Thus an aberration free image can be produced.
Volume 27, number 3
OPTICS COMMUNICATIONS
1.0
G1
December 1978
IS
CF
l
!
?
•
~
+
?'
'
IML SLIT i
~ ..... ' ,: ~ . , ! • +'
| I
:
.,,I!I+\ +l
\"°=' WHITE
,,
Fig. 3. Direct viewing of color reconstruction: H, holograms; IO, reconstructed image of color transparency; IS, image of
///
W.,TEU°HT
Fig. 2. Reproduction of color images: CF, fresh color film; IML, achromatic imaging lens; H, holograms.
The reconstructed color hologram image can then be recorded by a fresh color t'tlm or slide for the later use with conventional projectors.
slit. special effect is shared by all types of rainbow holograms. With this technique, it would be possible to store and reproduce color images in black and white t~dm, as similar to microfilm storage. Due to the simplicity of the process, especially in the reconstruction process of the color images, the technique is particularly adaptable for general library use.
5. Experimental results 4. Direct viewing This rainbow holographic technique also offers a very unique direct viewing capability. With all other existing color preservation techniques, some additional processings are required before the images in their original colors can be observed. With this proposed new technique, the original color image can be reconstructed and viewed directly with a simple white light illumination. In order to observe the image, the viewer merely places his eyes at the plane of the slit image as shown in fig. 3. When the viewer is at a correct viewing position, an image with true color reproduction can be observed. If the viewer moves transversely off this position, the image would appear in a color different from that of the original transparency. If the Viewer moves longitudinally off the correct observation plane, different shades of color will appear across the image in the well known manner of rainbow holograms. There is also an advantage in the direct viewing of the color images. Since the diffracted light converges to the slit image, the color image is exceedingly bright. This
As we pointed out before, by using symmetric systems in the construction and reconstruction process of the holograms, the images would be essentially aberration free. Nevertheless, the images would still suffer a certain degree of color blur [10,11] that inherently existed in the rainbow holographic process. Another factor that affects the resolution of the image is the presence of the narrow slit at the lens aperture. This would limit the image resolution achievable in that direction. However, through the proper design of the optical system, it is possible to minimize the amount of color blur and produce hologram images of very acceptable resolution. We shall discuss in a later paper, various design parameters and techniques, such as quasi-imaging configuration [ 11 ] and bandwidth compression, to decrease the amount of color blur and increase the maximum resolution of the system. In fig. 4, we have a black and white photograph of a color hologram image using the technique we described. The picture is of a field of tulips with a wide range of colors and the image if focused on the 309
Volume 27, number 3,
OPTICS COMMUNICATIONS
Fig. 4. Black and white photograph of a reconstructed color hologram image, white spot at left is white light source. two tulips at the foreground. We note that this color hologram image is the first one we produced and the optical parameters have not been optimally adjusted. The original slide is a 35 mm color transparency and a rainbow hologram is recorded on a Kodak 131 holographic plate. When the reconstructed hologram image is directly viewed, we see that the image appears very bright and the color is impressively vivid.
6. Conclusion We have presented a new technique for the archival preservation of color film with the one-step rainbow holographic process we developed. The technique offers several advantages over the existing techniques. First, the recording can be constructed by a one-step rainbow holographic process, it requires only a single
310
December 1978
set of films unlike the traditional technique of color preservation which requires three separate sets of negatives. Secondly, the new technique offers a unique capability of direct viewing process, without any additional processing step. Third, it requires only a simple white light source for the reconstruction, it is particularly suitable for library applications. In addition, because of the convergence natur~ of the rainbow holographic process, the reconstructed hologram image is extraordinarily bright. However, there is some degree of color blur inherent in the hologram image. We note that the amount of color blurring can be minimized to an acceptable degree, by the proper design of the optical system. We wish to acknowledge the partial support of the National Science Foundation (Grant Eng. 77-0788).
References [1] H. Chen, A. Tai and F.T.S. Yu, Appl. Opt., to be published. [2] H. Chen and F.T.S. Yu, Opt. Lett. 2 (1978) 85. [3] F.T.S. Yu and H. Chen, Optics Comm., to be published. [4] F.T.S. Yu, A. Tai and H. Chen, Appl. Opt., submitted. [5] S.A. Benton, J. Opt. Soc. Am. 59 (1969) 1545A. [6] E.N. Leith, Sci. Am. 235 (1970) 80. [7] C.S. Ih, Appl. Opt. 14 (1975) 438. [8] C.S. Ih, J. Opt. Soc. Am. 64 (1974) 1396A. [9] C.S. Ih, Appl. Opt. 17 (1978) 1059. [10] J.C. Wyant, Opt. Lett. 1 (1977) 130. [ 11 ] H. Chen, Appl. Opt., to be published.
OPTICS COMMUNICATIONS
December 1978
ARCHIVAL STORAGE OF COLOR FILMS BY RAINBOW HOLOGRAPHIC TECHNIQUE F.T.S. YU, Anthony TAI and Hsuan CHEN * Electrical and Computer Engineering Department, ICayneState University, Detroit, 114148202, USA
Received 7 August 1978
A technique of generating color holographic imageswith a one-step rainbow holographic process is described. This technique offers the capability of archival storage of color materials on a single black and white photographic film. The process is very simple to implement and it allows the reconstruction of the color image with a white light source. Although some degree of color blur is inherent with the rainbow holographic process, it can be minimized by the proper design of the optical system. A simple experimental result is also presented.
1. In~oducfion In an earlier paper [ 1], we have demonstrated a technique of generating color 3-dimensional images with the one-step rainbow holographic process [ 2 - 4 ] . We have shown that with a fairly simple optical arrangement, one could reconstruct a 3-dimensional image with faithful color reproduction using a black and white film as the recording medium. The reconstructed image was also exceedingly bright under ordinary white light illumination which is due to the convergence nature of the rainbow process [2,5,6]. The major disadvantage of this technique is the limited field of view restricted by the finite aperture of the imaging lens. This may be a serious restriction for the recording of 3-dimensional images. It is, however, relatively unimportant in the recording of 2-dimensional images. This process is, therefore, uniquely suitable for the recording of 2-dimensional color pictures, and in this paper, we shall apply it to the archival storage of color pictures. Archival storage of the finished color films has long been an unresolved problem for the major libraries and fdm industries all around the world. One reason is that the organic dyes used in the color fil.m are usually unstable under prolonged storage. This causes * With the Department of Physics, Saginaw Valley State College, University Center, Michigan 48710,
a gradual fading of the color in the original image. There are several ways to preserve the true color of the Film, but all of them possess certain disadvantages. For example, by the repetitive application of primary color filters, one can preserve the color image on three different rolls of the black of white Films. To reconstruct the original color image, a system with three different primary color projectors must be used for their respective Films. At the same time, the Films must be advanced in perfect unison and the images must be overlapped in perfect precision. Since the colors of the reproduced image are derived from the filtered light sources which are not subjected to fading like the organic dyes, the true colors of the image can be preserved. However, there are two major shortcomings with this method. First, the storage volume for each Film is tripled. Secondly, the reproduction system will be elaborate and expensive. Alternatively, one can use Fourier color holographic technique as was proposed by Ill [7--9], to store each color component into a single triple-exposure hologram. This would greatly reduce the required storage volume of the archives. However, in the reconstruction process of the color image, a system of three critically aligned lasers is required. This technique is therefore not suitable for the use as a direct viewing system for public usage in libraries. Also, there would inadvertently be some cut off of the high spatial frequency signals in the spatial filtering process, causing a marginal loss in resolution. 307
Volume 27, number 3
OPTICS COMMUNICATIONS
In this paper, we shall describe a technique of color image preservation using the one-step rainbow holographic technique that we have developed [2]. It may be the simplest and most efficient technique in use today. As with other color preservation techniques, this holographic process can be used to reproduce color images on a new color photographic film. It also allows the direct viewing of the color hologram images using only a simple white light source for illumination. This capability makes the rainbow holographic technique particularly suitable for library applications.
2. Holographic recording In our earlier paper [1] on the recording of color 3-dimensional images, we made use of an arrangement that would produce orthoscopic images. In the recording of 2-dimensional images, however, it is irrelevant whether the reconstructed images are orthoscopic or pseudoscopic, and we shall make use of an arrangement that produces pseudoscopic'images for our present application because of its greater simplicity and larger field of view [2,3]. The optical arrangement utilized in the construction of the color rainbow hologram is illustrated in fig. 1.
December 1978
A He-Ne laser emitting at wavelength 6328 A and two argon lasers, emitting at wavelengths of 5145 A and 4765 A respectively are used as the illuminating sources. The laser beams are attenuate individually with neutral density f'flters to compensate for the differences in the light intensities of the three laser lights and the spectral responses of the recording medium. The color film strip containing the color images to be recorded is mounted on a film transport and back illuminated by a fine diffuser. The diffusely illuminated color transparency is then imaged by an achromatic imaging lens through a narrow slit onto a plane close to the holographic film which is mounted on a light tight f'tim transport. For simplicity, a collimated reference beam is used in the construction of the holograms. The holographic recordings are then performed in a frame by frame basis with the two film transports advancing synchronously after each recording. The intensities of the three laser lights are adjusted to the appropriate levels such that the corresponding optimal exposure times for the three colors would be the same. Thus the photographic film is exposured to the three laser beams simultaneously through a single exposure. After the recording film is developed, a series of color rainbow holograms are formed on the film strip.
3. Image reconstruction M
BS
8S
BS
Io Fig. 1. Optical arrangement for hologram construction: M, mirror; BS, beam splitter; SHR, shutter; ND, neutral density filter; SF, spatial filter; CL, achromatic collimating lens; IML, achromatic imaging lens; O, object color transparency; IO, image of object; H, holographic film.
308
A collimated white light illuminating at the conjugate reference angle is used in the reconstruction. We found that the best result is obtained by using an optical system which is symmetric to that utilized in the holographic recording, as illustrated in fig. 2. When illuminated by the conjugate collimated white light, each of the three holograms formed by the different laser sources will be diffracted into continuous spectral bands of images. However, only the appropriate wavelengths would be able to propagate through the narrow slit and reconstruct the color hologram image at the output plane. We note that if a symmetric system is used in the construction and the reconstruction of the hologram, the light diffracted by the hologram would simply retrace the light path of the holographic recording process and produce the original image. We see that any aberration that may exist in the optical components would be automatically compensated. Thus an aberration free image can be produced.
Volume 27, number 3
OPTICS COMMUNICATIONS
1.0
G1
December 1978
IS
CF
l
!
?
•
~
+
?'
'
IML SLIT i
~ ..... ' ,: ~ . , ! • +'
| I
:
.,,I!I+\ +l
\"°=' WHITE
,,
Fig. 3. Direct viewing of color reconstruction: H, holograms; IO, reconstructed image of color transparency; IS, image of
///
W.,TEU°HT
Fig. 2. Reproduction of color images: CF, fresh color film; IML, achromatic imaging lens; H, holograms.
The reconstructed color hologram image can then be recorded by a fresh color t'tlm or slide for the later use with conventional projectors.
slit. special effect is shared by all types of rainbow holograms. With this technique, it would be possible to store and reproduce color images in black and white t~dm, as similar to microfilm storage. Due to the simplicity of the process, especially in the reconstruction process of the color images, the technique is particularly adaptable for general library use.
5. Experimental results 4. Direct viewing This rainbow holographic technique also offers a very unique direct viewing capability. With all other existing color preservation techniques, some additional processings are required before the images in their original colors can be observed. With this proposed new technique, the original color image can be reconstructed and viewed directly with a simple white light illumination. In order to observe the image, the viewer merely places his eyes at the plane of the slit image as shown in fig. 3. When the viewer is at a correct viewing position, an image with true color reproduction can be observed. If the viewer moves transversely off this position, the image would appear in a color different from that of the original transparency. If the Viewer moves longitudinally off the correct observation plane, different shades of color will appear across the image in the well known manner of rainbow holograms. There is also an advantage in the direct viewing of the color images. Since the diffracted light converges to the slit image, the color image is exceedingly bright. This
As we pointed out before, by using symmetric systems in the construction and reconstruction process of the holograms, the images would be essentially aberration free. Nevertheless, the images would still suffer a certain degree of color blur [10,11] that inherently existed in the rainbow holographic process. Another factor that affects the resolution of the image is the presence of the narrow slit at the lens aperture. This would limit the image resolution achievable in that direction. However, through the proper design of the optical system, it is possible to minimize the amount of color blur and produce hologram images of very acceptable resolution. We shall discuss in a later paper, various design parameters and techniques, such as quasi-imaging configuration [ 11 ] and bandwidth compression, to decrease the amount of color blur and increase the maximum resolution of the system. In fig. 4, we have a black and white photograph of a color hologram image using the technique we described. The picture is of a field of tulips with a wide range of colors and the image if focused on the 309
Volume 27, number 3,
OPTICS COMMUNICATIONS
Fig. 4. Black and white photograph of a reconstructed color hologram image, white spot at left is white light source. two tulips at the foreground. We note that this color hologram image is the first one we produced and the optical parameters have not been optimally adjusted. The original slide is a 35 mm color transparency and a rainbow hologram is recorded on a Kodak 131 holographic plate. When the reconstructed hologram image is directly viewed, we see that the image appears very bright and the color is impressively vivid.
6. Conclusion We have presented a new technique for the archival preservation of color film with the one-step rainbow holographic process we developed. The technique offers several advantages over the existing techniques. First, the recording can be constructed by a one-step rainbow holographic process, it requires only a single
310
December 1978
set of films unlike the traditional technique of color preservation which requires three separate sets of negatives. Secondly, the new technique offers a unique capability of direct viewing process, without any additional processing step. Third, it requires only a simple white light source for the reconstruction, it is particularly suitable for library applications. In addition, because of the convergence natur~ of the rainbow holographic process, the reconstructed hologram image is extraordinarily bright. However, there is some degree of color blur inherent in the hologram image. We note that the amount of color blurring can be minimized to an acceptable degree, by the proper design of the optical system. We wish to acknowledge the partial support of the National Science Foundation (Grant Eng. 77-0788).
References [1] H. Chen, A. Tai and F.T.S. Yu, Appl. Opt., to be published. [2] H. Chen and F.T.S. Yu, Opt. Lett. 2 (1978) 85. [3] F.T.S. Yu and H. Chen, Optics Comm., to be published. [4] F.T.S. Yu, A. Tai and H. Chen, Appl. Opt., submitted. [5] S.A. Benton, J. Opt. Soc. Am. 59 (1969) 1545A. [6] E.N. Leith, Sci. Am. 235 (1970) 80. [7] C.S. Ih, Appl. Opt. 14 (1975) 438. [8] C.S. Ih, J. Opt. Soc. Am. 64 (1974) 1396A. [9] C.S. Ih, Appl. Opt. 17 (1978) 1059. [10] J.C. Wyant, Opt. Lett. 1 (1977) 130. [ 11 ] H. Chen, Appl. Opt., to be published.