Image Representation

2.3 Color Image Representation

A color digital image is typically represented by a triplet of values, one for each of the color channels, as in the frequently used RGB color scheme. The letters R, G, B stand for red, green, and blue. The individual color values are almost universally 8-bit values, resulting in a total of 3 bytes (or 24 bits) per pixel. This yields a three-fold increase in the storage requirements for color versus monochrome images.

Naturally, there are a number of alternative data structures for multicolor image data. The so-called pixel-interleaved (or meshed) and color-interleaved (or planar) formats are the most widely used. Less frequent are row-wise or column-wise interleaving methods. In a pixel-interleaved format, the raw image data is contained in a 2D array, with every element being a list of three values:

In the color-interleaved format, the raw data is separated into three 2D matrices, one for each of the color channels:

The three primary colors may be used to synthesize any one of 2²⁴ or approximately 16 million colors. In the following we show a small selection of combinations of {r, g, b} color values. In each colored square the red and blue color values are varied in increments of

, with the amount of green increasing in the same manner from left to right. Note that we use a normalized value range for specifying color values. Thus when using a Mathematica graphics directive, such as RGBColor, the values must be in the range 0≤ r, g, b ≤1.

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Equal amounts of each of the three colors result in a shade of gray. Here is a grayscale ramp from an RGBColor directive.

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