Color photographic film and paper use subtractive color synthesis to reproduce the real world either directly with transparency film or with an intermediate negative. Color photographs begin as black and white negatives. Color film consists of three layers of emulsion, each layer basically the same as in black and white film, but sensitive only to one third of the spectrum (reds, greens or blues). Thus, when colored light exposes this film, the result is a multilayered black and white negative.

After the negative images are developed, the undeveloped emulsion remaining provides positive images by "reversal." The remaining emulsion is exposed (chemically or with light) and the film developed a second time with a different developer. As it converts the light-sensitive silver compounds to metallic silver, the developer becomes oxidized and combines with "coupler" compounds to produce dyes.

The three dyes formed, one in each emulsion layer, are the subtractive primaries yellow, magenta and cyan. All silver is then bleached out and each layer is left with a positive color image. Thus reds in the subject produce a heavy silver deposit in the red-sensitive layer in the negative, but no trace on the other layers. Then after reversal, only yellow and magenta remain which together make red. As shown in the illustration, the cyan is all but gone.

After the film is processed and the silver is removed, what remains is called a "Dye Cloud" and as shown in the "enlarged" illustration below the clouds interaction creates a red color. Transparency film shows this interaction as positive colors and what appears to the eye as grain are in fact dye clouds. Color negative paper also makes dye clouds, though they respond to negative, or subtractive colors, and the interaction of the clouds in the negative combine with the clouds in the paper to reproduce an image. All this softness works to minimize the appearance of "grain". This is the reason behind the creation of the grainmaker filter. I'm always interested in discussion, scientific or otherwise. You can Email me at jscruggs@bway.net (additive)(autochrome)(color)(grainmaker specifics)(screens)(subtractive)