Color Theory

Color Theory Color photographs begin as black and white negatives. Color film consists of three layers of emulsion, each layer basically the same as in black and white film, but sensitive only to one third of the spectrum (reds, greens or blues). Thus, when colored light exposes this film, the result is a multilayered black and white negative After the negative images are developed, the undeveloped emulsion remaining provides positive images by reversal. The remaining emulsion is exposed (chemically or with light) and the film developed a second time with a different developer. As it converts the light-sensitive silver compounds to metallic silver, the developer becomes oxidized and combines with coupler compounds to produce dyes. The three dyes formed, one in each emulsion layer, are the subtractive primaries yellow, magenta and cyan.

All silver is then bleached out and each layer is left with a positive color image. Thus reds in the subject produce a heavy silver deposit in the red-sensitive layer in the negative, but no trace on the other layers. Then after reversal, only yellow and magenta remain which together make red. As shown in the illustration, the cyan is all but gone. After the film is processed and the silver is removed, what remains is called a Dye Cloud and as shown in the enlarged illustration below the clouds interaction creates a red color. SUBTRACTIVE COLOR SYNTHESIS uses paints, dyes, inks, and natural colorants to create color by absorbing some wavelengths of light and reflecting or transmitting others. This subtractive action is the basis of photographic filters, almost all films and color papers, and photomechanical reproduction in color.

White light is composed of all visible wavelengths, which can be divided into three primary-color bands, red, green and blue. A colorant that absorbs one wavelength band has the combined color of the other two; it is the complement of the color it subtracts from white light. Thus: Primary Primary Combined Color Colors Color of the Absorbed Unaffected Subtractive Complementary Red Blue & Green Cyan Green Blue & Red Magenta Blue Red & Green Yellow The complementary colors are the control colors of subtractive color synthesis; thus, the dyes in color filters and emulsions, and the inks (process colors) used in photomechanical reproduction are cyan, magenta, and yellow. A single complementary produces its own color. Two complementaries in equal strengths produce a primary color because each absorbs a primary–e.g., magenta and yellow absorb green and blue, respectively, leaving red to be seen.

Combinations of unequal subtractive strengths produce intermediate colors from white light. A combination of all three complementaries produces black (full strengths) or gray (lesser equal strengths) because all colors are subtracted. In color filtration this produces neutral density. Primary-color lights can be additively mixed to produce colors, but primary-color dyes, inks, or filters do not permit selective color control by subtractive action because each absorbs the other two primaries equally. The complementary colors permit subtractive control of each of the three primaries individually; like additive synthesis, this corresponds with the three-color theory of vision.(1) Color photographic film and paper use subtractive color synthesis to reproduce the real world either directly with transparency film or with an intermediate negative.

Color photographs begin as black and white negatives. Color film consists of three layers of emulsion, each layer basically the same as in black and white film, but sensitive only to one third of the spectrum (reds, greens or blues). Thus, when colored light exposes this film, the result is a multilayered black and white negative. Color photographic film and paper use subtractive color synthesis to reproduce the real world either directly with transparency film or with an intermediate negative. Color photographs begin as black and white negatives. Color film consists of three layers of emulsion, each layer basically the same as in black and white film, but sensitive only to one third of the spectrum (reds, greens or blues).

Thus, when colored light exposes this film, the result is a multilayered black and white negative. After the negative images are developed, the undeveloped emulsion remaining provides positive images by reversal. The remaining emulsion is exposed (chemically or with light) and the film developed a second time with a different developer. As it converts the light-sensitive silver compounds to metallic silver, the developer becomes oxidized and combines with coupler compounds to produce dyes. The three dyes formed, one in each emulsion layer, are the subtractive primaries yellow, magenta and cyan.

All silver is then bleached out and each layer is left with a positive color image. Thus reds in the subject produce a heavy silver deposit in the red-sensitive layer in the negative, but no trace on the other layers. Then after reversal, only yellow and magenta remain which together make red. As shown in the illustration, the cyan is all but gone. After the film is processed and the silver is removed, what remains is called a Dye Cloud and as shown in the enlarged illustration below the clouds interaction creates a red color.

Transparency film shows this interaction as positive colors and what appears to the eye as grain are in fact dye clouds. Color negative paper also makes dye clouds, though they respond to negative, or subtractive colors, and the interaction of the clouds in the negative combine with the clouds in the paper to reproduce an image. All this softness works to minimize the appearance of grain. This is the reason behind the creation of the grainmaker filter. Screen processes are basic to our perception of the world around us in a variety of communications media, from the dots on your monitor to the pictures you see in magazines.

Screens are basically just dots arranged either in a pattern or stochastically (random). A long time ago, photography too, used a variety of screen processes from colored glass beads melted into a glass base to dyed potato starch, as in the autochrome process. All these processes work because the human eye at a certain distance doesn’t see the individual dots but rather perceives their cumulative effect The most common of the color screen processes is that used for photomechanical reproduction by offset and web presses. Color separation negatives form a rosette pattern, using subtractive color, in addition to black, in a repetitive order to synthesize reality. As you can see from the illustration, the color halftone screens are rotated to form the pattern.

These negatives are used to form a image that is burned onto printing plates to carry the ink on the press. By varying the density of the dots color the cumulative effect of say lack of cyan density, gives the appearance of red, by you visually assimilating the combination of the yellow and magenta inks, which in conjunction with the dots small size makes you perceive a continuous tone image with a red color. Modern color photographic film works by using dyes in the form of clouds (grain) as a stochastic dot reproduction of exposed reality. Old photographic film methods used a variety of screens. One of the earliest was that created by Louis Dufay in France 1910 Called the Dioptichrome plate (aka Dufaycolor,later) which consisted of a mosaic of alternating green and blue dye squares crossed at right angles by a pattern of parallel red dye lines, each element measuring only 0.0002 in (0.05mm) in width.

This screen was coated with a panchromatic emulsion, the material was exposed through the base, the screen, and exposing the emulsion from the back. Processed to reversal, the result was a positive transparency. (1) Other methods involved the use of woven fabrics, ruled lines and resists, among others Additive Color Synthesis is the method of creating color by mixing various proportions of two or three distinct stimulus colors of light. These primary colors are commonly red, green, and blue, however they may be any wavelengths to stimulate distinct receptors on the retina of the eye. The distinguishing features of additive color synthesis are that it deals with the color effects of light rather than with pigments, dyes, or filters, and that the stimuli come from separate monochromatic sources.

The most common example of additive color synthesis is the color television screen, (or RGB monitor), which is a mosaic of red, green, and blue phosphor dots; at normal viewing distances the eye does not distinguish the dots, but blends or adds their stimulus effects to obtain a composite color effect. This is an enlarged example of additive color synthesis from a RGB type source. (a) Equal stimulus proportions of two primary colors create a secondary color 1 Red + 1 Blue = Magenta 1 Blue + 1 Green = Cyan 1 Green + 1 Red = Yellow (b) Equal stimulus proportions of all three primaries create white: 1 Red + 1 Blue + 1 Green = White (c) Unequal proportions of two or three primaries create other colors: 2 Red + 1 Green = Orange 2 Green + 1 Red = Lime 1 Blue + 1 Green + 4 Red = Brown All color s …