What is color addition?

Answer 1

Presumably, you are referring to Additive Color. White light can be split into a spectrum of colors with a prism. White light can also be reconstructed by projecting "pure" green, red, and blue light onto a screen. By altering the proportions of those three colors, it is possible to recreate any color. Additive color processes use sharp cutting (very narrow band) color filters to record a black-and-white record of the relative proportions of red, green, and blue light in a scene (panchromatic film is necessary for this). The resulting images are processed or printed to positive, then projected back through an identical set of filters to recreate the original color. There are a variety of ways of doing this. The early Autochrome process used dyed grains of starch placed in a layer against the film emulsion, and used a reversal process to produce striking color transparencies. Kodak's original Kodacolor film from 1928 used lenticular impressions in the base of the film to serve as lenses that focused an image of a three-banded filter onto pixel-like points in the film. Again, processed to reversal and projected back through the filter, the black-and-white image reproduced the color very accurately. Others used color screens, and tri-color separation cameras took three different images simultaneously on three different plates through the three color filters. These could be used to make high-quality color prints through a variety of processes. The downside of additive color is that it is light-hungry. Each of the filters removes approximately two-thirds of the white light that falls on it. The red filter, for example, passes only red, while absorbing the blue and green content of the light. With such large light loss, it takes a very bright projection source or a short projection distance with a conventional source to reproduce the image. However, the color quality is excellent.