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Color depth, also known as bit depth, is either the number of bits used to indicate the color of a single pixel, or the number of bits used for each color component of a single pixel. When referring to a pixel, the concept can be defined as bits per pixel (bpp).
8-bit color graphics are a method of storing image information in a computer's memory or in an image file, so that each pixel is represented by 8 bits (1 byte). The maximum number of colors that can be displayed at any one time is 256 per pixel or 2 8 .
The 4-bit per pixel (4bpp) format supports 16 distinct colors and stores 2 pixels per 1 byte, the left-most pixel being in the more significant nibble. [5] Each pixel value is a 4-bit index into a table of up to 16 colors. The 8-bit per pixel (8bpp) format supports 256 distinct colors and stores 1 pixel per 1 byte.
In 15-bit high color, one of the bits of the two bytes is ignored or set aside for an alpha channel, and the remaining 15 bits are split between the red, green, and blue components of the final color. Each of the RGB components has 5 bits associated, giving 2⁵ = 32 intensities of each component. This allows 32768 possible colors for each pixel.
Usually, there are 5 bits allocated for the red and blue color components (32 levels each) and 6 bits for the green component (64 levels), due to the greater sensitivity of the common human eye to this color. This doubles the 15-bit RGB palette. The 16-bit RGB palette using 6 bits for the green component:
High-end digital image equipment are often able to deal with larger integer ranges for each primary color, such as 0..1023 (10 bits), 0..65535 (16 bits) or even larger, by extending the 24 bits (three 8-bit values) to 32-bit, 48-bit, or 64-bit units (more or less independent from the particular computer's word size).
A 2-bit indexed color image. The color of each pixel is represented by a number; each number (the index) corresponds to a color in the color table (the palette).. In computing, indexed color is a technique to manage digital images' colors in a limited fashion, in order to save computer memory and file storage, while speeding up display refresh and file transfers.
To reconstruct each compressed 4-pixel by 4-pixel block, the 16-bit luminance bitmap is consulted for each block. Depending on whether an element of the bitmap is 1 or 0, one of the two 8-bit indices into the lookup table is selected and then dereferenced and the corresponding 24-bit per pixel color value is retrieved. [1] [2] [3]