16 September 2019, Name-day for Edyta, Kamil, Korneliusz. Anniversaries.

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Color depth

Color depth or bit depth, is a computer graphics term describing the number of bits used to represent the color of a single pixel in a bitmapped image or video frame buffer. This concept is also known as bits per pixel (bpp), particularly when specified along with the number of bits used. Higher color depth gives a broader range of distinct colors.

Color depth is only one aspect of color representation (formally, the gamut: which colors can be expressed), expressing how finely levels of color can be expressed (formally, gamut depth); the other aspect is how broad a range of colors can be expressed. The RGB color model, as used below, cannot express many colors, notably saturated colors such as yellow. Thus, the issue of color representation is not simply "sufficient color depth" but also "broad enough gamut".

With relatively low color depth, the stored value is typically a number representing the index into a color map or palette. The colors available in the palette itself may be fixed by the hardware or modifiable within the limits of the hardware (for instance, both color Macintosh systems and VGA-equipped IBM-PCs typically ran at 8-bit due to limited VRAM, but while the best VGA systems only offered an 18-bit (262,144 color) palette from which colors could be chosen, all color Macintosh video hardware offered a 24-bit (16 million color) palette). Modifiable palettes are sometimes referred to as pseudocolor palettes.

As the number of bits increases, the number of possible colors becomes impractically large for a color map. So in higher color depths, the color value typically directly encodes relative brightnesses of red, green, and blue to specify a color in the RGB color model.

While some high-end graphics workstation systems and the accessories marketed toward use with such systems, as from SGI, have always used more than 8 bits per channel, such as 12 or 16 (36-bit or 48-bit color), such color depths have only worked their way into the general market more recently.

Most of today's TVs and computer screens form images by varying the intensity of just three primary colors: red, green, and blue. Bright yellow, for example, is composed of equal parts red and green, with no blue component. However, this is only an approximation, and is not as saturated as actual yellow light. For this reason, recent technologies such as Texas Instruments's BrilliantColor augment the typical red, green, and blue channels with up to three others: cyan, magenta and yellow. Mitsubishi and Samsung, among others, use this technology in some TV sets. Assuming that 8 bits are used per color, such six-color images would have a color depth of 48 bits.