Technical Information Bulletin
Updated June 18, 2002
Color printing requires controlling the color components of a light source to achieve correctly balanced prints.
Modern additive printers use a set of standard dichroic mirrors to separate or combine the light from a tungsten-halogen bulb into its red, green and blue components. The mirrors have a multilayer coating of dielectric material that reflects a specific wavelength region while transmitting other regions. Adjustments are made to the mirrors to achieve the desired color balance on the final print.
A subtractive printer uses a white light source to produce properly balanced prints. Combinations of color filters control the amounts of red, green and blue light.
Printing that requires a lot of scene-to-scene color corrections is very difficult on a subtractive printer because a new color-correcting filter pack must be physically inserted between the light source and the printing aperture for every correction.
Overall light changes (intensity changes) are made by using a variable aperture or a neutral density filter.
Technical Information Bulletins provide information of limited or specific application. Responsibility for judging the applicability of the information for a specific use rests with the end user.