The negative may be used to produce a positive image, often called a print, or photograph, in which the light and dark areas of the object and the image correspond. The positive is produced by first projecting the negative onto a photosensitive paper. When this is done by direct contact, i.e., placing the negative and photosensitive paper together, the positive produced is the same size as the negative. When a system of lenses is interposed, the positive image may be enlarged or reduced. After this the latent image on the photosensitive paper is developed by a process similar to that used on the negative.
In most color films there are three layers of emulsions, each sensitive to a different color of light and each capable of forming a different color dye when developed. There are many development processes in use, but nearly all use paraphenylene-diamine derivatives. In one process the exposed film is made into a positive color transparency, in another a negative from which positive prints are produced. In both processes the finished product contains three layers, each one containing an image in a different color. The superposition of these images reproduces the colors of the photographed object.
Polaroid photography uses a more complex process, by which the image diffuses from the top layer, where it is originally captured, to lower layers where it activates appropriate dyes to recreate the recorded image (see Land, Edwin).
The Columbia Electronic Encyclopedia, 6th ed. Copyright © 2012, Columbia University Press. All rights reserved.