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CHAPTER 11: COLOR SCIENCE |
Blue-green called cyan.
Red and violet combined produces purple. Each color joins the adjacent color without visible difference. Purple joins violet into red
and hence circle of color named by Newton. Mixing light can then be explained in a circle, part of circumference for each color and white light at the center. Tw diagonally opposite color producing white light. This is a subject matter of physics and psychology. Color is sensation or human perception.
PRIMARY COLORS:
Black is absent of colors. White is combination of all colors. Red came first recognized, then yellow, green and eventually blue. Other name of colors came later in the language. The French scientist Mariotte chose the primary colors to be red, green and blue. It seems all colors can be produced by three primary colors, one of the three primary colors can't be produced by any combination of the orher two a nd white light is produced by combination of the three in some proportion.
ADDITIVE MIXING
Mixing colored lights (as opposed to pigments) is called additive mixing. Any sopectral color or any color of Newton's circle is produced by some proportion of three primary colors.
Two colors of dimetrically opposite parts in Newton's circle poroduce white light and are called complementary colors. Examples of coplementary colors are,
yellow and blue, green and magenta, rec and cyan (blue-green)
W = Y + B
Y = W - B
C = W - R
M = W - G
White is omitted. Often, the complimentary to white is said to be minus the primary. So,
Y = -B
C = -R
M = -G
If we move from white to a color where one of the primaries is absent, we find ourselves in a color commplementary to the missing primary color.
SUBTRACTIVE MIXING
The negative primaries which result in yellow, magenta and cyan are the colors used for mixing of the pigments, called subtractive mixing. The name is used because pigments work by absorption, taking out certain wavelengths from incident light. When pigments are used, what adds up is the light removed. Cyan pigment absorbs red and yellow pigment absorbs blue and magenta pigment absorbs green. If cyan and yellow pigments are mixed, result is green.
IMPLICATIONS: Light of wavelength 580 nm is yellow. But yellow light does not always consist of the one wavelength of 580 nm. A matching yellow light may be produced by combination of green and red light with 580 nm absent in it. Such matching colors as green and red for yellow, which differ in their spectrum are call METAMERS. We find no one to one correspondence between the two situations as far as wavelengths are concerned. Color printing, color photography and color TV are possible because of the Laws of Color Science just described. We need to work with only 3 primary colors to produce allshades of colors. There are a vast number of these.