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A color value is a set of numbers that uniquely identify a color within a color space. Color values are like map coordinates that identify a location with latitude and longitude.

Color values take either the form of integers within a certain range, a percentage from 0% to 100%, or a floating point number (float) typically from 0 to 1. The lowest value represents black (no contribution to the color), while the highest value represents the fullest contribution, with all values combining to make white.

Color depth—the number of bits used to represent a color value—directly affects how many color values are usable in an image. The higher the color depth, the more intermediate color values between black and white there are. The following formula defines how many possible colors are available:

Color values = 2 ^ (color depth × [number of color channels])

A typical JPEG image (8 bits per channel, 3 channels) therefore contains up to 2^(8×3) = 2^24 = 16,777,216 possible colors per pixel.

Color values by color spaceEdit

RGBEdit

The most commonly seen values are for the RGB color space, used by all monitors. In 24-bit RGB, values range from 0 to 255, which can also be represented by the hexadecimal numbers 00 to FF. A trio of values are used, each representing Red, Green, and Blue. For instance, a modest green color can be represented by the values {32, 240, 0}, which is written in hex notation as {20, F0, 0} or #20F000.

High resolution RGB values use floating point numbers, with 0 representing monitor black and 1 representing monitor white. Because high-resolution images can define colors outside of monitor black and white, color values can also be negative (extremely dark) or greater than one (extremely bright). Such extreme values are typically clipped to 0 or 255 in 24-bit depth. The same green color above can be represented with the values {0.125466, 0.937480, -0.000371}.

HSBEdit

HSB is a peculiar color space where the Hue value is represented by degrees, and can wrap around from 359° back to 0°. Saturation and Brightness values are represented with integers from 0 to 100, or percentages. Some programs use increased number precision (e.g. "0.1" rather than "0") for greater resolution.

The same green color above can be represented with the values {112°, 100, 94}.

CMYKEdit

The CMYK color space uses values from 0 to 1 (or 0% to 100%), which can be directly translated to a percentage of ink coverage. Because cyan, magenta, and yellow can combine to make black, a separate black ink is used to lower the total volume of ink used. It is bad practice to use 100% of all four inks, so Photoshop uses algorithms to keep a pixel's total color value under about 300%.


LabEdit

In the Lab color space, the Lightness value typically ranges from 0 to 1 (or 0% to 100%), while the a and b values are floats from -1 to 1.


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