单选题
{{B}}Colors{{/B}}
There are two ways to
create colors in a photograph. One method, called additive, starts with three
basis colors and adds them together to produce some other colors. The second
method, called subtractive, starts with white light (a mixture of all colors in
the spectrum) and, by taking away some or all other colors, leaves the one
desired.
In the additive method, separate colored lights combine
to produce various other colors. The three additive primary colors are green,
red and blue (each providing about one-third of the wavelengths in the total
spectrum). Mixed in varying proportions, they can produce all colors. Green and
red light mix to produce yellow; red and blue light mix to produce magenta;
green and blue mix to produce cyan. When equal parts of all three of these
primary-colored beams of light overlap, the mixture appears white to the
eye.
In the subtractive process, colors are produced when dye
(as in paint or color photographic materials) absorbs some wavelengths and so
passes on only part of the spectrum. The subtractive primaries are cyan (a
bluish green), magents (a purplish pink), and yellow; these are the pigments or
dyes that absorb red, green and blue wavelengths, respectively, thus subtracting
them form white light. These dye colors are the complementary colors to the
three additive primaries of red, green and blue. Properly combined the
subtractive primaries and absorb all colors of light, producing black. But,
mixed in varying proportions, they too can produce any color in the
spectrum.
Whether a particular color is obtained by adding
colored lights together or by subtracting some light from the total spectrum,
the result looks the same to the eye. The additive process was employed for
early color photography. But the subtractive method, while requiring complex
chemical techniques, has turned out to be more practical and is the basis of all
modern color films.