We can control and modify the development process, and hence relative densities in the negative, by changing such variables as solution strengths, developer temperatures, and times in each processing step. Next, we must use the negative to make a separate, positive, black and white print, in which dark tones correspond to darker areas in the scene, and light tones to light areas. We do this during the printing process. We pass white light through the negative onto the print material. Contrast determines whether a scene with variable colors and brightness appears flat or presents wide ranges of light-dark areas that aid in discriminating features.
Contrast is the ratio of density to the logarithmic value of exposure.
As we explained in the Introduction, a red filter, for example, passes mainly radiation in the red and nearby regions of the visible spectrum. We can project multispectral positive transparencies for different color bands using several color filters onto color print paper to produce natural or false color composites, as described in the Introduction. How we use color film to produce color images involves some different concepts, although many of the same factors and mechanisms are still valid. Starting with the three additive primary colors, red, green, and blue, or the subtractive primary colors, yellow, cyan and magenta, we can make other colors by using the principles of either the color addition or the color subtraction process. Color Models Additive Color Model Subtractive Color Model Color addition works when we superimpose the primary colors on one another.