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ADDITIVE COLOUR
An additive color model involves light emitted directly from a source or illuminant of
some sort. The additive reproduction process usually uses red, green and blue light to
produce the other colors. Combining one of these additive primary colors with another in
equal amounts produces the additive secondary colors cyan, magenta, and yellow.
Combining all three primary lights (colors) in equal intensities produces white.
Varying the luminosity of each light (color) eventually reveals the full gamut of those
three lights (colors).
Computer monitors and televisions use a system called optical mixing and cannot be
considered additive light because the colors do not overlap. The red green and blue pixels
are side-by-side. When a green color appears, only the green pixels light up.
When a cyan color appears, both green and blue pixels light up.
When white appears all the pixels light up. Because the pixels are so small and close
together our eyes blend them together, having a similar effect as additive light. Another
common use of additive light is the projected light used in theatrical lighting (plays, concerts, circus shows, night clubs, etc.).
Results obtained when mixing additive colors are often counterintuitive for people accustomed to the more everyday subtractive color system of pigments, dyes, inks and other
substances which present color to the eye by reflection rather than emission.
For example, in subtractive color systems green is a combination of yellow and blue, in
additive color, red + green = yellow and no simple combination will yield green.
It should be noted that additive color is a result of the way the eye detects color, and is
not a property of light. There is a vast difference between yellow light, with a wavelength
of approximately 580 nm, and a mixture of red and green light. However, both stimulate
our eyes in a similar manner, so we do not detect that difference. (see eye (cytology),
color vision.)
The first permanent color photograph, taken by James Clerk Maxwell in 1861.
James Clerk Maxwell with his color top that he used for investigation of color vision and
additive color
James Clerk Maxwell is credited as being the father of additive color. He had the photographer Thomas Sutton photograph a tartan ribbon on black-and-white film three times,
first with a red, then green, then blue color filter over the lens. The three black-and-white
images were developed and then projected onto a screen with three different projectors,
each equipped with the corresponding red, green, or blue color filter used to take its image. When brought into alignment, the three images (a black-and-red image,
a black-and-green image and a black-and-blue image) formed a full color image, thus
demonstrating the principles of additive color.