Feb 16, 1990 - Getting more for less: a new opponent color technique for ... red and white are all that would be predicted by conventional color mixture theory. ... color process, then "for exact color reproduction the three filters should have ...
Young RA. Getting more for less: a new opponent color technique for two-channel color displays. In: Perceiving, Measuring, and Using Color: SPIE 1990:1250:132-43. http://dx.doi.org/10.1117/12.19707
QSPIE- he International Society for Optical Engineering
Reprinted fim
Perceiving, Measuring, and Using Color
15- 16 February 1990 Santa Clara, California
Volume 1250 ~ 1 9 9 by 0 the Sodety ofPhoto optical ~ m t i o Engineers n Box 10, Bellingham, W a s h i i 98227 USA. Telephone 206/676-3290.
Getting more for less: a new opponent color technique for two-channel color displays Richard A. Young General Motors Research Laboratories, Computer Science Department Warren, Michigan 48090-9055
ABSTRACT A new technique is described for making color liquid crystal displays with only two color channels. Red and white channels were tried first, expanding upon the photographic approach of Edwin Land. A test image simulating the liquid crystal display was produced on a standard color cathode ray tube. With shades of red and white arranged in alternating diagonals of a checkerboard pattern, observers saw more colors than predicted by simple color mixtures of red and white -- for example green was seen by all observers. But why white and red channels? One brightness and one color opponent channel (one which switches between opposing colors such as red and cyan) better describes the major two components in the color vision system. A test image with one white channel and one opponent redfblue channel in a checkerboard pattern gave rise to an even wider range of colors than did the Land-type display. Photographic print and slide film versions of the displays also showed the effects. In the liquid crystal display, the opposing colors can be produced by using a dichroic polarizer. Such two-channel displays have the advantages of higher spatial resolution or lower cost than conventional color displays. A prototype liquid-crystal two-channel display should be developed.
1. INTRODUCTION
1.1 Land's experiments Take a picture of a colored scene through a green filter onto black-and-white film, and project it with no filter, creating a white display. Do the same with a red filter, projecting with a red filter. Superimpose the two displays, and more hues than mixtures of red and white are produced, even though only red and white lights are used, as Edwin Land showed in 1959.133 (Studies in two-color redwhite projection had been done prior to Land's work, but with moving picture~.)~95 Land's first channel is formed by recording the original scene through a red filter onto blacldwhite positive film, and then projecting it through the same red filter. Land's second channel is formed by recording the the original scene through a green filter onto blacwwhite positive film, and then projecting it through no filter (see Figures 1 and 2).
1
I
G
Fig. 1. Schematic example of the two input channels using Land's film method. The original colored scene on the right is recorded on two blacwwhite positive films through red and green filters respectively, to form the images depicted schematically on the left. 132 / SPlE Vol. 1250 Perceiving, Measuring, and Using Color (1990)
Fig. 2. Land output. The films are placed in projectors and the green filter is removed. When the red and white output images are overlapped to form one display, more hues than just red and white (or their mixtures) are seen by observers with normal color vision. Of course, mixtures of just red and white are all that would be predicted by conventional color mixture theory. In our own attempts to replicate the Land effect using his exact filters with complex scenes, it is easy to demonstrate informally that you can obtain especially good greens, browns, reds, and whites, but there is a weakness for most observers in the cooler end of the spectrum, particularly deep blues. These informal results are depicted schematically in Fig. 2, where the blue (B) input leads to a gray output. Other hues are generally given the same names as in the original, although there can be subtle variations in saturation and brightness.6-10 Attempts to explain the Land two-channel experiments have been made over the yearsY6-lo but to date there has not yet been a'fullysatisfactory explanation of the "induced" colors. They are probably associated with colored shadow effects, which are quite powerful perceptually (even more so than simultaneous color contrast effects), but these are also unexplained. It is unclear how Land's "Retinex" theory, developed later, would apply to his earlier two-color experiments.
1.2 Liquid crystal implementation of the Land effect A liquid crystal method for implementing Land's effect was recently proposed.11 The red image is shown in one set of diagonals in a matrix display, and the white image in the other (Fig. 3).
Fig. 3. A portion of a Land-type matrix display with two channels: red and white.
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Fig. 4. A portion of a conventional display with three channels: red, green, and blue. A composite color segment is formed of only two elements (red and white) in the Land-type display, while it requires three elements (red, green, and blue) in the conventional display (Fig. 4). Hence the effective spatial resolution for the Land-type liquid crystal display is 50% better in both the horizontal and vertical directions than for the RGB display in Fig. 4, for an equivalent total number of elements. Alternatively, if cost is most critical, one can reduce the total number of pixels by 1/3, thereby saving 1/3 on the electronics and memory requirements, and still maintain equivalent resoluhon to the RGB display. This checkerboard matrix color method is reminiscent of mosaic-screen-plate color photography, l 2 used in making plates and films for color photography some fifty or which as noted by ~ a c ~ d a r nwas more years ago by Lumiere, Agfa, Dufay, Ansco, and DuPont. The lenticular Kodacolor film sold for amateur motion pictures in the 1920s used this mosaic principle.12 The same plates and films used for the original camera exposure that recorded the pictures was used for the final display, by additive light combination. By placing red filters over one-half the pixels in a liquid-crystal-matrix,and no filters over the over half, could Land-type display conditions be produced with additive color mixture? Such a technique would require only a single light source, with no special optics needed. Since one-third fewer color elements are needed for equivalent resolution to an RGB display, and also only a single color overlay mask needs to be used instead of three, one would expect significant cost savings with this approach, assuming an acceptable range of colors could be produced. l l 1.3 Opponent colors and orthogonal channels But what's so special about white and red? Is there a better choice of "basis functions" for 2-channel color? Let's look to nature for insights. It has of course been known for many years that opponent colors (e.g. redlgreen, blue/yellow) are useful and even necessary for describing human color perception.13 Could there be some way to use opponent colors in a display? There might be even a greater advantage if orthogonal channels could somehow be used, since these are the most efficient possible means for information encoding.24 Also, orthogonal channels would eliminate the strong interactions that now make it so difficult to calibrate and reproduce colors using conventional methods. The color channels in additive RGB media such as color television displays, or subtractive CYM (cyan-magenta-yellow) media such as print or film, have highly correlated spectra, producing complicated and difficult-to-control interactions when attempting color matching, calibration, or balancing. Another advantage of an orthogonal basis set is pointed out by M a c ~ d a m--l ~ if photographic material that had constant spectral sensitivity were used for any additive color process, then "for exact color reproduction the three filters should have spectral transmittances that are orthogonal color-matching functions." The theoretical study of orthogonal color functions has had a long history. ~ a c ~ d a m calculated l~ several triplets of orthonormal functions using C.I.E. 1931 color mixture data. yilmaz15 noted that the sensitivity curve for brightness as a function of wavelength resembled a Gaussian function, and sug-
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gested using Gaussian derivatives as orthogonal basis functions for color. He noted the resemblance of such curves to the Hering opponent-colors sensitivity curves. ~ i l m a z l ~also ~ l 6developed a detailed explanation of the Land two-color effect and color constancy, based on a set of Lorentz transformations of these coordinates. On the psychophysical side, Ingling and Tsoul7 show how an orthogonal combination of the three cone pigments can explain much psychophysical data. Cohen18 solved for orthogonal components of the Munsell chip set. This experiment was later replicated on a much larger Munsell chip sample with more modem analytic techniques.l9 Cohen and ~ a p p a u (see e also ~ r i l l ~orthogonalized l) the colorimetric (CIE) primaries and came up with opponent-like processes, which they relate to the Hering opponent primaries. MacAdaml2 raised the objection however that "Because at least two of three orthogonal functions must have negative values of significant magnitude, whereas light filters cannot have negative transmittances, the requirement of exact color reproduction cannot be filled by any additive, mosaic-screen or lenticular process." However, the biological vision system may have found a clever solution to this problem, which may be adaptable for use in color displays.
1.4 The brain's orthogonal color channels In the case of the primate visual system, young22 analyzed 441 spectral response curves from a large sample of neurons in the brain.23 He found the principal components, which are an optimized orthogonal basis function set, underlying those spectra. The frrst two components explain the most data possible with just two components. The first principal component, which is similar to a brightness or "white/black" component, accounts for about 60%of the total activity in the visual pathways from the eye to the brain (Fig. 5).
Relative
0.3
"
.. 0 + 400
:-
500 600 700 Wavelength (nm) Fig. 5. Spectral curve of the first principal component in the brain.
The data points (squares) in Fig. 5 represent the first principal component in the lateral geniculate body (LGN) in the brain of the monkey. The solid curve is a weighted sum of the human cone pigment spectra, after raising them to the l/3 power (here termed "power cones"). Such a power function represents well the nonlinearity-incone responses.25 Fig. 5 shows that there is a good fit between the human cone data and the first principal component in the monkey brain. The fact that two different sets of data correspond so well lends plausibility to the claim that this curve is indeed the first principal component of color vision.
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Fig. 6 suggests that this first component may be associated with the human percept of brightness. We know from human psychophysical studies that the human perception of brightness is associated with the 1/3 power of the stimulus intensity. If we take the 1/3 power of the human luminosity function, we get in Fig. 6. The fmt principal component (Fig. 5) is rotated 13 degrees, so it the curve labelled "~um*fl" peaks at 555 nm as does the luminosity function.22 It is plotted as the curve labelled "Neural" in Fig. 6. Note the correspondence between the neural curve and the " ~ u m l f l "or "brightness" curve. At long wavelengths they overlap completely. At short wavelengths the deviation may be related to differences between the monkey and human visual systems in short wavelength sensitivity.
Relative Sensitivity
500 600 Wavelength (nm)
400
700
Fig. 6. The first neural principal component may be related to "brightness".
Relative Neural S ike &ange
400
500 600 Wavelength (nrn)
700
Fig. 7. Spectral curve of the second principal component in the brain. The second component, orthogonal to the fust, is spectrally opponent -- positive on one end of the spectrum, and negative on the other (Fig. 7). (It is here termed "orange/cyanWfor convenience, because
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The second component, orthogonal to the first, is spectrally opponent -- positive on one end of the spectrum, and negative on the other (Fig. 7). (It is here termed "orangelcyan" for convenience, because it is intermediate between the usual redlgreen and yellow/blue opponent vectors,22 but no special significance should be attached to the use of those color names in association with this second component. Perceived hue is believed to arise from the components in combination).n This second component represents about 30% of the remaining neural activity. The third component (not shown) is also opponent, but triphasic -- positive in the center, and negative at the two ends of the spectrum. Since it represents only about 6% of the remaining activity, it can be safely ignored with little loss in the color information as represented in the nervous system. A principal component analysis of the human cone photopigments has been made by Buchsbaum and Gottschalk, 24 and Young, 25 with similar results. There is a close association between the cone components and the brain components in Figs. 6 and 7, as described by ~ o u n g . ~ 5 The white/black and two color opponent channels used by television engineers to encode color information for commercial broadcast represents a related solution to the same problem of optimal color encoding in a limited bandwidth. Indeed, the relative bandwidths assigned by television engineers to the luminance and chromatic components is not much different than that occurring in the primate visual system as revealed by the above analysis. Of course, the engineers designing color television broadcast signals likely optimized their channels by visual examination of picture quality, rather than by detailed examination of the vision literature. They probably adjusted the spectra and bandwidths assigned to the luminance and chrominance channels until they observed the optimal picture quality within the limitations they had. Of course, matched filter theory would predict that the optimum picture quality would occur when the relative bandwidths they assigned to the luminance and chrominance channels matched that occurring within their own visual systems. Another reason is that with limited bandwidth, whether due to broadcast transmission constraints, or to the limited number of neurons available in the optic tract for sending messages from the eye to the brain, then a similar solution is likely. After all, only one optimal solution can exist from a functional information standpoint, regardless of whether the color information is to be transmitted electronically or neurally. Such results therefore suggest that if one had to choose only two channels to represent color information, the optimum two would be (1) a unimodal one, peaking in the center of the spectrum, and (2) a bimodal one, differencing the two ends of the spectrum. One can ignore the third triphasic component, and theoretically lose only about 6% of the color gamut. As noted by Young?2 any rotation of the first two components could also describe the major neural activity, and could also be used as basis functions without loss of generality. Indeed, a rotation of the first two components by about 30 degrees produces the response spectra of the redlgreen and blue/yellow opponent cells in the visual ~~stem.22 Of course, neurons could use negative as well as positive values to encode opponent processes, if higher levels could decode the temporal differential in activity from the spontaneous level of neural activity. However, another way to encode opponent processes is by having matched pairs of units, which respond in an opposing manner to spectral information. Thus for the predominant whitelblack channel, the total cell population is divided into two equal groups -- half the cells fire to a white light onset, while the other half fues to a black light onset (i.e. a white light offset). Or, dividing the population in another way, half the cells fue to long wavelengths, and half to short.22 These two tendencies (which are the first two principal components) combine to produce chromatically opponent cells which exist in pairs: greedred or blue/yellow. For every cell which fues to red-appearing light and inhibits to greenappearing light, there tends to be another cell which does the opposite, and likewise for blue/yell0w.~3 Thus, even without the direct ability to encode negative numbers, an opponent process can be made be having units which operate in a push-pull or complementary fashion. This analysis led directly to the suggested opponent display methodology to be described below, which makes use of a dichroic polarizer to produce an opponent color signal
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The conjecture is made that the orthogo la1 basis functions used by the brain to encode color information may also provide an optimal encoding basis function set to represent color information in display technologies. 1.5 Opponent colors in a liquid crystal display? Reasoning thus from the brain's solution, we may have found a way to get around MacAdam's objection that negative transmittances are required to get an o~-rhogonalopponent-type display. Perhaps we can merely arrange our color channel to encode color in an opponent or reciprocal fashion. In particular, the above analysis suggests that a "white/black" or brightness channel and one color opponent channel best describes the major two components in the brain's early visual pathway. This observation suggests a new opponent-color two-channel display method, as shown in Fig. 8.
Fig. 8. Opponent matrix display with two channels, white and opponent redlblue. Fig. 8 shows a liquid crystal opponent display capable of displaying the'first two components of color information in this manner. The even diagonal pixels operate in the normal fashion, using conventional linear polarizers, and so produce the blacldwhite channel. The odd diagonal pixels, which will serve the function of the opponent channel, makes use of a dichroic polarizer. The dichroic polarizer material has the special property of changing color depending upon the angle of polarization of light incident upon it. Thus when the liquid crystal cell is turned on, the light coming out of the dichroic polarizer does not change from black to white, but instead changes from one color to another. These colors may be chosen from a wide variety of possible pairs by choosing different dichroic materials. For example, the pixels can be changed between red and green, blue and yellow, red and blue (or almost any other two colors), thus implementing the opponent channel color effect.
1.6 CRT simulation To test the perceived colors arising from such displays, I simulated both Land-type and opponenttype color displays on a standard RGB cathode ray tube (CRT), using a checkerboard display method with a standard RGB image. Land-type effects have been observed with television CRT images previbut not using a checkerboard display method. However, to our knowledge the use of ously, 26s27,2*.29 one white and one color opponent channel has not been previously done on a CRT or any other means of color production. I wish to point out that the CRT demonstration here was done only as a means of testing for the eventual effects we hope to obtain using a liquid-crystal implementation. 2. METHOD
A 256 by 256 pixel RGB test image from the UCLA image library was selected for analysis. A calibrated Hitachi color monitor was driven by a 24 bit Raster Technologies Model 1/25 display driver under computer control. In the Land-type CRT experiments, the green image memory buffer was sent equally to the red, green, and blue guns in the odd diagonal pixels, creating the white display. The red memory buffer was sent to the red gun in the even diagonal pixels, creating the red display (the blue and
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green guns were not turned on at these pixels). The checks were small enough so the observer visually merged the two displays in an additive manner. In the opponent CRT experiments, the average of the red, green, and blue memory buffers at each spatial location was stored as the fust channel. These values were normalized so the peak value was at 255, the maximum value of the display. This channel was sent equally to the three guns in the odd diag: onal pixels, producing the whiteblack image. For example, if red had 50, green had 100, and blue had 150 at a given address, then a value of 100 would be stored as the first channel, and sent equally to the drivers for the red, green, and blue guns, producing white at that pixel when viewed in isolation. The difference of the red and blue buffers (also normalized to a peak of 255) was stored as the opponent channel. The red gun was driven directly by this channel, and the blue gun by its negative (the green gun was turned off by assigning it a value of 0). If the final output signal to a gun was negative, it was clamped at 0. For example, if the red memory buffer had a value of 200 and the blue a value of 100, then a value of 100 would be stored in the opponent channel, 100 would be sent to the red gun, and 0 to the blue gun. If the blue buffer had 200 and the red 100, then -100 would be stored in the opponent channel, 100 would be sent to the blue gun driver, and 0 to the red gun driver. Thus the red and blue guns always operated in an inverse manner, and so comprised only one color channel. It is worth noting that the use of conventional RGB cathode ray tubes to simulate the liquid crystal display in this manner causes spatial resolution to be three times worse than it would be with liquid crystals, since six color elements must be used to create the two color channels, rather than just two color elements as in the liquid-crystal method (see Fig. 9). Nonetheless, what we were mainly interested in was seeing if we could produce induced color effects and get a wide range of color. If so, it would then be worthwhile to implement a liquid crystal two-channel display based on these principles.
Liquid Crystal
CRT
-White/ Red or Black Blue 3 pixels + 3 pixels
=6
White1 Red/ Black Blue 1 pixel + 1 pixel = 2
Fig. 9. A liquid crystal implementation will have 3 times better resolution than the CRT simulation. Although the main purpose of this research is to develop display technologies, color prints of the images were necessary for this published report. Photographs were therefore taken with a Matrix Instruments Color Graphic Recorder on Kodacolor Gold 100 print film. Three photographs of every test image were taken on a single roll of film, and printed on a single "gang" sheet, as a control for variations in the photography, developing and printing. (Figs. 10A-D were all in fact on a single negative, as were Figs. 11A-D). The final prints were all professionally developed, and strict instructions were given to ensure that all prints were treated identically in the development process. The test photographs (Figs. 10E and 11E to be described in the Results) were shown to seventy subjects. As controls, the images were randomly presented to different subjects on the left and right sides, and under varying conditions of illumination from daylight to fluorescent. None of these conditions affected the results. Seventy subjects were asked "Which image has the wider range of colors?" in a simple two-alternative forced choice procedure. Five subjects asked for a definition of "range" and for them the question was rephrased to: "Which image has the greater variety of colors?"
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3. RESULTS In the Land-type display using the checkerboard method on the CRT, the results were encouraging. More hues than red and white were seen, particularly green, browns, and golds. However, not much blue was observed, corresponding with our preliminary investigations using Land's film methods. Printed versions of the Land display can be seen in Fig. 10 (color plate). Fig. 10A shows the original RGB image. Fig. 10B is the Land "white" image (the green buffer sent equally to the R, G, and B guns), and Fig. 10C is the Land "red image. These two images were electronically superimposed in the composite image in Fig. 10D. A 2 times enlargement is seen in Fig. 10E. One example of the Land-type induced color effects is that most people report seeing the woman's dress as green, even though there is no "green" observable in Figs. 1OB and C (only red and white). The man's suit was not seen by any observers in Fig. 10E as "blue," and also the wall was seen as more reddish-white than whitish-blue as in the original. Of course, the pictures you see in this color plate have gone through a transformation from the CRT screen to film, then to a photographic print, then to a color separation, and then to final printing, so the color effects may be considerably changed from those on the CRT screen. Nonetheless the color effects should still be generally visible as described. In the opponent display, the results were even more encouraging. In addition to the range of hues viewed in the Land display, the man's suit was now seen as a dark blue, and the wall appeared more bluish-white, among other differences. All observers comparing the two displays under simultaneous viewing on two matched monitors saw a wider range of colors in the opponent-type display than in the Land-type display. Printed versions of the opponent display can be seen in Fig. 11. The image in Fig. 11A again shows the original as a control (this should appear the same as Fig. 10A). Fig. 11B is the whiteblack image, and Fig. 11C is the opponent color image (red minus blue in this case -- see Methods). The composite image is Fig. 1ID, enlarged 2 times in Fig. 11E. In Fig. 1lE, the dress was still seen as green by the subjects, even though as before there was no "green" in the two channels observed individually. However, now the man's suit is seen by most observers as "blue". Also, the white in his collar was reported as a better white by some subjects than in Fig. 10E, as was the white on the wall. Golds and browns as in the chair and rug are seen as not much different than in Fig. 10E. Several observers also said that they saw the woman's scarf as more reddish-orange than red in the opponent image than in the Land image. A total of 54 of the 70 subjects (77%, or about 3 to 1) reported that the opponent print (Fig. 11E) had a greater range of colors than the Land print (Fig. 10E). Fig. 12 shows an 8 times enlargement of a portion of the opponent-type display to show the underlying checkerboard structure in the opponent image Fig. 12B, and in the final composite image Fig. 12C. Photographic slide versions of the white and opponent images were superimposed in a single slide projector beam (unlike the case with Land's original demonstration where two separate beams are required). Similar color results were obtained as from direct viewing of the displays, although the saturation of the colors was somewhat degraded compared to the direct CRT display. Transparency versions of these images for superimposition on an overhead projector were also produced. The effects could still be seen, but they were weaker, probably because of the lower overall image quality with transparencies as opposed to film. For example, it was difficult to keep sharp edges on the checks in the checkerboard patterns, which caused bleeding of one overlay into the other. In the opponent CRT Q i slay, ~ many other weighted sum and difference combinations of the red, green, and blue signals also produced a wide range of color. The simple sum and difference channels we chose for testing were just to demonstrate the feasibility of the basic approach. Further research in optimizing the colors of the orthogonal channels will be useful once a liquid crystal display is developed.
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4. DISCUSSION
The Land-type and the opponent-type methods gave rise to multiple perceived hues in a cathode ray tube simulation of a liquid-crystal two-channel checkerboard display. These results were also seen in film and print renditions of the images. Observers saw a wider range of colors using the opponent method than with the Land method. An opponent-type display can be implemented using liquid crystals with a dichroic polarizer overlay?O Of course, much greater compression of color information (to less than 2 bitshixel) can be achieved by customizing the color vectors to each individual image .31 What we seek to achieve here, however, is a general color compression method that can be applied to any image. We also provide a new and simple color display methodology that may allow such compressed images to be shown with cost and resolution advantages over standard RGB displays, with minimal loss in perceived color.
These results are quite preliminary, and represent only an initial feasibility study. They should be extended to a wider variety of color images, and to other types of color components. The next major step in this research however will be for a prototype liquid-crystal twochannel display to be developed based on these principles. We expect such a display will be much better quality than our simulation, because of the better spatial resolution that can be achieved. Potential applications include automobile instrument panels, as well as portable color television or computer displays where cost is a critical factor. 5. CONCLUSIONS
1. The Land two-color method gives rise to multiple induced hues in a matrix-type CRT display. 2. Film or color prints of the CRT display also show the effects. 3. Using an opponent color method leads to an improvement in the range of colors seen. 4. A dichroic polarizer may allow an opponent color channel to be implemented inexpensively in a liquid crystal display.
6. ACKNOWLEDGMENTS I especially thank J. Troxell for initially suggesting a matrix color display and helpful collaboration throughout. I also thank L. Peruski for software development on the CRT display program, G. Smith and N. Vaz for suggesting use of a dichroic polarizer, and D. Poynter for helpful discussion and color calibration of the CRT monitors. Portions of this paper were previously presented at the 1989 Optical Society of America meetings in Orlando, ~1orida.W 7. REFERENCES E. H. Land, "Color vision and the natural image. Part I," Proc. Nut.Acad. Sci., vol. 45, pp. 115-129.1959. E. H. Land, "Color vision and the natural image. Part II," Proc. Nut. Acad. Sci., vol. 45, pp. 636-644,1959. E. H. Land, "Experimentsin color vision," ScienrificAmerican, May 1959. W. F. Fox and W. H. Hickey, "Improvements in kinematographicapparatus," British Patent No. 636, issued July, 1914. A. Cmwell-Clyne, Colour Cinematography, London, 1951, pp. 260-261. M. M. Woolfson, "Some new aspects of color perception," IBM Journal, vol. 3, pp. 313-325, Oct. 1959. D. B. Judd, "Appraisal of Land's work on two-primary color projections." J. Opt. Soc. Amer., vol. 50, pp. 254-268, Mar. 1960. 8. R. Belsey, "Color perception and the Land two-color projections," J. Opt. Soc. Amer., vol. 54, pp. 229-231, Apr. 1964. 9. D. E. Pearson, C. B. Rubiistein, and G. J. Spivak, "Comparison of perceived color in two-primary computer-generated artificial images with predictions based on the Helson-Judd formulation," J. Opt. Soc. Amer., vol. 59, pp. 644-658, May, 1969. 10. D. E. Pearson and C. B. Rubinstein, "Range of perceived hues in two-primary projections," J. Opt. Soc. Amer., v0l.60. pp. 1398-1403, Oct 1970.
1. 2. 3. 4. 5. 6. 7.
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11. J. A. Troxell and R. A. Young, "Matrix addressable displays using color perception effects," GMR Research Publication #GMR-6908, January 2,1990. 12. D. L. MacAdarn, Color Measurement, Theme and Variations, Second revised edition, Springer-Verlag,Berlin. 1985, pp. 189-192. 13. D. Jameson and L. M. Hurvich, "Opponentchromatic induction: experimental evaluation and theoretical account," J. Opt. Soc. Amer., vol. 46, pp. 46-53, 1961. 14. D. L. MacAdarn, "Orthogonal color-mixture functions," J. Opt. Soc. Amer., vol. 44, pp. 713-724,1954. 15. H. Yilmaz, "Color vision and a new approach to general perception," Biological Prototypes and Synthetic Systems, vol. 1, ed. by E. E. Bernard, Plenum Press,N.Y., 1962. 16. H. Yilmaz, "On color perception," Bulletin of Mathematical Biophysics, vol. 24, pp. 5-29, 1962: 17. C. R. Ingling and B. H. Tsou, "Orthogonal combination of three visual channels," Vision Res., vol. 17, pp. 1075-1082, 1977. 18. J. B. Cohen, "Dependency of the spectral reflectance curves of the Munsell color chips," Psychon. Sci., vol. 1, pp. 369370,1964. 19. J. P. S. ParWrinen, "Characteristic spectra of Munsell colors", J. Opt. Soc. Amer., vol. 6, 1989. 20. J. B. Cohen and W. E. Kappauf, "Color mixture and fundamental metamers: Theory, algebra, geometry, application," American Journal of Psychology, vol. 98, pp. 171-259.1985. 21. Brill, M. H. "Decomposition of Cohen's matrix R into simpler color invariants," Amer. J. Psychology, vol. 98, pp. 625634.198516. 22. R. A. Young, "Principal-componentanalysis of macaque lateral geniculate nucleus chromatic data." J. Opt. Soc. Amer., VOI. 3, pp. 1735-1742,1986. 23. R. L. De Valois, I. Abrarnov, and G. H. Jacobs, "Analysis of response patterns of LGN cells," J. Opt. Soc. Amer., vol. 56, pp. 966-977.1966. 24. G. Buchsbaum and A. Gottschalk, "Trichromacy, opponent colours coding and optimum colour information transmission in the retina," Proc R. Soc. Land. B , vol. 220, pp. 89-1 13.1983. 25. R. A. Young, "Principal-componentanalysis of human cone spectra," Address, Optical Society of America, Rochester. N.Y., October 1987. 26. W. L. Hughes, "Some color slide and color television experiments using the Land technique," IEEE Trans. on Broadcasting, vol. BC-6, pp. 29-33, Mar. 1960. 27. N. W. Daw. "Color television method and apparatus employing different sets of target phosphors, one of which luminesces in a single color and another of which luminesces in different colors," U. S. Patent 3,271,512, Sept. 6, 1966. 28. N. Gold, "Color television system employing superimposed red and white images," U. S. Patent 3,443,025, May 6, 1969. 29. C. A. Barlow. Jr. "Color display system." U. S. Patent 3,560,636, Feb 2. 1971. 30. R. A. Young. J. R. Troxell, G. W. Smith, and N. A. Vaz, "New techniques for two-channel color displays using liquid crystals," Address, Optical Society of America, Orlando, Florida, October 20, 1989. 31. J. B. Demco and Gershon Buchsbaum, "Image compression application of a simultaneous Karhunen-Loeve transforn~ation in space and color," Address, Optical Society ofAmerica, Orlando, Florida, October 20, 1989.
8. COLOR PLATE FIGURE LEGENDS Fig. 10. A cathode-ray tube simulation of a Land-type liquid crystal display. A. The original image.
B. The Land-type white channel, in the odd diagonal pixels. C. The Land-type red channel, in the even diagonal pixels. D. The composite white and red images. E. A 2 times electronic enlargement of the composite image. Fig. 11. A cathode-ray tube simulation of an opponent-type liquid crystal display. A. The original image (should appear same as Fig. 10A). B. The averaged "white" channel in the odd diagonal pixels. C. The red/blue opponent channel in the even diagonal pixels (see Methods). D. The composite white and red~blueopponent images. E. A 2 times enlargement of the composite image. Most people see a wider range of color here than in Fig. 10E. Fig. 12. Eight-times enlargement of a portion of the opponent-type display. A. The original image. B. The redblue opponent channel. (The white channel is not shown). C. The composite image. The underlying checkerboard structure should be visible in B and C.
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Fig. 11
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Fig. 12
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