COLOR THEORY AND COLOR IMAGING-SYSTEMS - PAST, PRESENT AND FUTURE

James Clerk Maxwell demonstrated the first color photograph in a lectu re to the Royal Society of Great Britain in 1861. He used the demonstr ation to illustrate Thomas Young's idea that human vision uses three k inds of light sensors. This demonstration led to a Teat variety of col or photographic systems using both additive and subtractive color. Tod ay, we have image-capture devices that are photographic, video, still, and scanning. We have hardcopy printers that are electrophotographic, inkjet, thermal and holographic, as well as displays that use cathode ray tubes, liquid-crystal and other light emission color devices. The major effort today is to get control of all these technologies so tha t the user can, without effort, move a color digital image from one te chnology to another without changing the appearance of the image. The strategy of choice is to use colorimetry to calibrate each device. If all prints and displays sent the same colorimetric values from every p ixel, then the images, regardless of the display, would appear identic al. The problem with matching prints and displays is that they have ve ry different color gamuts. A more satisfactory solution is needed. In my view, the future emphasis of color research will be in models of hu man vision. The purpose of these models will shift from calculating co lor matches to calculating color sensations. All the technologies list ed above work one pixel at a time. The response at every pixel is depe ndent on the input at that pixel, regardless of whether the imaging sy stem is chemical, photonic, or electrical. Humans are different. The c olor they see at a pixel is controlled by that pixel and all the other pixels in the field of view. Human color vision uses a spatial calcul ation involving the whole image. Except for human vision, all other co lor systems have the same output from a single input. In other words, if an input pixel has a value of 128, and the image processing changes that value to 155, then all pixels with 128 in will have 155 out. Hum an vision is unique among color imaging systems because a single input value (128) will generate a range of output values (0, or 55, or 128, or 255), depending on the values of other pixels in the image. Despit e the remarkable progress in our ability to control the placement of d yes and pigments on paper, we must now return to the study of Maxwell' s interest-color theory-for the next advancements in color systems. In the future, we will see more models that compute the color appearance from spatial information and write color sensations on media, rather than attempting to write the quanta catch of visual receptors.