About Digital Images: Raster Bit Depth

DEFINITION
A bit depth refers to the number of memory bits used to store color data for each pixel in a raster image (all pixels require the same number of bits in any given image). The number of bits determines the range of colors the image may have (see below).

EXPLANATION
A raster image consists of a rectangular grid of picture elements (pixels). Each pixel uses the same amount of memory to store its color data. This amount of memory us called the bit depth of the image. Greater bit depths are required to represent finer gradations of color.

bit depth vs number of colors
To store higly colored images, more bits are required. This also increases file size.

1 bit = 2 colors (black and white) "bit map"
2 bits = 4 colors
4 bits = 16 colors
8 bits = 256 colors
16 bits = "thousands"
32 bits = "millions" (aka "true color" since each pixel can have it's own color).

bit depth vs file size
It would seem natural to make images as deep as possible, but this also increases file size. A black and white drawing requires only one bit per pixel to store all the available color information. If 32 bits per pixel are used for the image, the file will be roughly 32 times as large as it needs to be. The extra bits add nothing to the image quality.

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