Capturing a black cat in shade: the past and present of Retinex color appearance models

John J. McCann, Bernice E. Rogowitz, Thrasyvoulos N. Pappas
2002 Human Vision and Electronic Imaging VII  
memory and adaptation could not explain the colors in ambiguous displays seen for the first time with so few photons. 3 Land knew spatial factors were important, but he did not know how to put the model of human color vision together. In his process of persistent exploration he made the critical observation that color appearance correlated with the triplet of lightness appearances in long-, middle-, and shortwave light. 4 ,5 This idea created a halfway point between the physical measurement of
more » ... cal measurement of cone quanta catch and color appearance. If we found a physical model whose output correlated the appearances ranging from white to black, then that mechanism could be used three times in parallel to predict colors. This observation transformed the study of color to a need for understanding how the eye sees whites, grays and blacks. Land's observation still stands. The triplet of apparent lightnesses correlates with color. The observation is important because a variety of different phenomena can influence lightness, such as simultaneous contrast, the Cornsweet effect, assimilation, and spatial blur of the retinal image. Regardless of the cause of the lightness shifts, when two identical physical objects look different, color appearances correlate with their L, M, S lightnesses. 6, 7 In an effective color assimilation display there are two sets of nine square redbrown patches on a yellow and blue striped background. On the left the red-brown patches fall on top of the yellow stripes and on the right they fall on the blue stripes. The left patches appear a purple red, while the right ones appear a yellow orange. In other words, the left patches appear more blue and the right ones more yellow. Color assimilation displays exhibit larger color effects than color contrast. 8 In assimilation, predominantly black surrounds make grays appear darker, while in contrast, black surrounds make grays appear lighter. Figure 1 shows the color display and the R, G, B separations for this effective color assimilation display. Identical square patches appear different colors. In the R separation the corresponding patches are lighter on the right; in the G separation the patches on the right are lighter; in the B separation the patches are darker on the right. Whenever ABSTRACT As a part of the Symposium "Retinex at 40" 1 , this paper recounted the research on capturing real-life scenes, calculating appearances and rendering sensations on film and other limited dynamic-range media. It describes: the first patents, a hardware display used in Land's Ives Medal Address in 1968, the first computer simulations using 20 by 24 pixel arrays, psychophysical experiments and computational models of color constancy and dynamic range compression and the Frankle-McCann computationally efficient Retinex image processing of 512 by 512 images. It includes several modifications of the original approach including recent models of human vision and gamut-mapping applications. This paper emphasizes the need for parallel studies of psychophysical measurements of human vision and computational algorithms used in of commercial imaging systems.
doi:10.1117/12.469530 dblp:conf/hvei/McCann02 fatcat:sw5xjeurdbgftap4zpm2q3payu