The grayscale can be described with a series of single numbers, each of which represents the density of a single pixel. The illustration below displays 256 discreet values of gray, the darkness of each pixel in this case, determined by an 8 bit number from 0 to 255. Since we are dealing with a single ink (black), only one value is needed for each pixel.

So how can we identify any one of the infinite number of colors? "Teal" or "olive" don't mean much to a computer, indeed may be ambiguous to the paint store owner or thread shop proprietor. But XX Company Paint #43, or BestThreads #465, do provide a precise way to obtain a specified color - at least that manufacturers version thereof (in that specific dye lot).

We do need a system to describe the variety of colors in the spectrum in a way the computer can understand and manipulate. Three of the popular systems in use are described below.

1. HSL - numerical values for the hue, saturation, and lightness of the color
2. CMY - the percentages of the "primary" colors cyan, magenta, and yellow
3. RGB - the level of each of the "primary" colors red, green, and blue

As usual, there is a "gotcha". Even if we can devise and specify a precise number or number combination for a color, the hardware manufacturers AND software developers must combine the elements described below in precisely the right combinations or the color will differ on each monitor or from each printer.

HUE The color wheel is a familiar artists tool. Why not describe colors by their angular position on the wheel? If red is arbitrarily assigning a value of zero degrees - then yellow becomes 60 green, 120 cyan, 180 blue, 240 and magenta, 300 Since orange is half-way between red and yellow, it becomes 30 degrees or just 30. Colors also have an attribute which describes the "amount of pigment" or percentage of pure color . It is called SATURATION. Zero saturation means no color, only grayscale. LIGHTNESS - describes the scale from darkest to lightest. Orange becomes brown as lightness is decreased.

CMY Anyone familiar with photographic color printing has an intimate knowledge of the use of cyan, magenta, and yellow filters. The relationship between C(yan)M(agenta)Y(ellow) and R(ed)G(reen)B(lue) is illustrated at the right. Passing white light through a cyan and magenta filter will permit blue light to pass. Color printers work in much the same way, applying the correct proportions of cyan, magenta, and yellow ink to produce the desired color. Since the black produced by the application of the three colors is rather muddy, black ink is usually added, hence we have CMYK, where K stands for black. Use a magnifying glass to study a color picture in a magazine. RGB CRTs (video monitors and TVs) use red, green, and blue dots to create the spectrum. Red and blue combine to make magenta; blue and green to make cyan; red and green to create yellow. Hard to believe? Look at the yellow area on your screen with a magnifying glass. While doing that, look at the surrounding area where the presence of all three, RG&B, combine to give the appearance of white. You will see below that white is produced by the presence of all three in the RGB color scheme, and the absence of all three in the CMY color scheme.

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