OUTLINE OF PHOTOGRAPHY 9 



the subject. Thus the blue-green positive subtracts blue-green or nonred from the 

 white light. Since white light may be made up of blue-green and its complementary 

 red, the result of subtracting blue-green from a white screen is the same as adding 

 red to an unilluminated screen. Similarly the magenta positive subtracts nongreen 

 from the white light; yellow subtracts nonblue-violet from the white light. 



In the final subtractive print, red portions of the subject are represented by yellow 

 and magenta superposed; blue is represented by blue-green and magenta; and green 

 is represented by blue-green and yellow superposed. Where there was no color in 

 the subject, there is no deposit of color on the final print and thus the white light by 

 which the result is viewed passes through the positives unobstructed. Where there 

 was black in the subject, all three colors are superposed in the final print and therefore 

 the result is white light minus magenta, blue-green, and yellow. Since the wave- 

 lengths represented by these three colors cover the entire visible spectrum, all wave- 

 lengths to which the eye is sensitive are subtracted, and none of the white light is 

 reflected or transmitted to the eye. This portion of the image appears black in 

 consequence. 



Since there is always some color in an additive picture but since there may be no 

 color in portions of the subtractive print, the latter is brighter and more contrasty. 



Unlike the additive material in which many small filters are a part of the material, 

 Kodachrome is a color film in which the colors come about in another way. Koda- 

 chrome is a subtractive material. It is made up of three distinct layers of color 

 material each substantially sensitive to only a portion of the spectrum. As a part of 

 the processing of the film these layers are dyed in colors complementary to the colors 

 they recorded when the exposure was made. 



