Digital Camera Peripherical System

To register and reproduce a color we can define its composition as the sum of the basic colors that make it up –definition (a). Therefore, we need to separately register the presence of each primary color and then sum the three obtained red, green and blue images. This is the additive system, used in digital photography, television and video. It reproduces any color as a sum of different proportions of red, green and blue. Observe a computer or television monitor under a magnifying glass when it's turned on. Every point of the screen is actually made up of a triad of matches of the primary colors that, when excited by there respective signal (an electron beam), emit a greater or lower intensity light. If a zone of the image is blue, only blue matches will turn on with the rest of them staying off; if it's yellow, blue is turned off and red and green are on, etc. A computer or television screen superposes and mixes the signal of three positive images of the basic colors. Seen separately, each one of them is a light image of only one primary color of variable intensity (only in combination with the other two), or black were not present. On the other hand, film doesn't use the additive system because it's not easy to superpose three primary positives on a same support .

More concretely: if we want to photographically reproduce a scene with the additive system we'd have to make a black and white negative that registers each one of the primary colors (putting a filter of each color in three different shots). Afterwards, from the negatives we create three positive transparent images tinted with their corresponding color; these color images would have the aspect of slides of the respective color in there place of the scene, and black in the zones it's not present. Now it's necessary to superimpose the three images to reproduce the scene with it's original colors: we place each transparency in a projector and make the three images coincide on a white screen. The sum of the different intensities of the basic colors reproduces all the colors of the original scene: through a photographic reproduction of the scene with the additive process.

This system is very complicated: it requires separately registering and reproducing three superimposed positive images of the primary colors. In TV this is achieved through the decomposition of the image in a plot of very thin vertical lines of the alternating basic colors.

Film can't group three positive images on the same support without a plotting system. We can only do it by separately projecting three images. To be convinced of this, try putting the three transparencies of our example in a same projector; now, a same light has to adopt all the tones of the scene. Not only is it not possible through a sandwich of three primary positive images, but the projectors light won't even be able to pass. Any of the layers only lets the light of it's color through (one third of the spectrum) and neutralizes the other two . Starting from the same source of white light, we cant ass red without neutralizing the green and blue, because the primary colors have nothing in common