| Additive and Substractive Color
by Hal Byron Becker
Username
HBB
Nikonian
in the USA
tell
a friend about this How to Improve Your Photography article
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INTRODUCTION
I prepared these charts as an aid to a few people I am tutoring in basic
color management concepts. This is not meant to be a rigorous
treatment of color theory or management, simply an introduction for
those interested.
GLOSSARY for the illustrative images and text
The Primary (Additive) colors, the basic, are Red, Green, and Blue; colors perceived by the human eye/brain system.
R = Red
G = Green
B = Blue
W = White
The Subtractive colors: are colors produced by selectively subtracting the three primary colors from white light.
C = Cyan
M = Magenta
Y = Yellow
K = Black (B already used for Blue)
ADDITIVE COLOR/FILTERS
The human eye is sensitive to three primary colors: Red, Green, and Blue. If three projectors are equipped with filters, one with Red, one with Green, and one with Blue, and their images are converged (added) on a white screen, the image above appears. The black background simulates the portion of the screen not illuminated in the dark room.
The three primary colors are easily seen.
Example: Red equals White minus Green minus Blue.
In shorthand:
R = W - G - B
G = W - R - B
B = W - R - G
Where the three primary colors overlap in pairs, the three subtractive colors: Cyan, Magenta, and Yellow appear. (See Subtractive Filters in the following page)
Example: Cyan equals Green Plus Blue.
In Shorthand:
C = G + B
M = R + B
Y = R + G
Where all three primary colors overlap in the center, white (W) appears.
W = R + G + B
The three primary colors are used in television sets, computer monitors and other devices that create the color perceived by the human eye/brain system by using projected light. By varying the three colors individually over a wide range, an enormous spectrum of colors can be created (Color space), ranging from black, the absence of all colors, to white, the presence of all three primary colors in equal intensity.
In eight-bit color depth, each of the three primary colors can have a value of 0 (zero) to 255, for a total of 256 shades. The total number of colors using red, green and blue equals 256 x 256 x 256 = 16,777,216 combinations. If all three primary colors are present in equal amounts less than 255 (pure white), the perceived color will be gray. All three colors at 127 (approximately one-half of 255) will produce a medium gray. Each of all three at 0 (zero) produces black, the absence of color.
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