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Color 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.
Indexed color
Direct color As the number of bits increases, the number of possible colors becomes impractically large for a color map (a 20 bit depth would require more memory to store the colormap than is required to store the pixels themselves). 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. HighColor Highcolor or HiColor is considered sufficient to provide life-like colors, and is encoded using either 15 or 16 bits: LCD Displays Truecolor Truecolor can frequently mimic many colors found in the real world, producing 16.7 million distinct colors. This approaches the level at which the human eye can distinguish colors for most photographic images, though image manipulation, some black-and-white images (which are restricted to 256 levels with Truecolor) or "pure" generated images may reveal the limitations. 32-bit color "32-bit color" is a misnomer when regarding display color depth. A common misconception is that 32-bit color produces 4,294,967,296 distinct colors. In reality, 32-bit color actually refers to 24-bit color (Truecolor) with an additional 8 bits either as empty padding space or to represent an alpha channel. Considering red, green, and blue use the same amount of bits for their respective color (with the exception of 16-bit color), the total bits used will be a multiple of 3: like 15-bit color (5 bits each) and 24-bit color (8 bits each). The reason for using empty space is that all but the newest modern computers process data internally in units of 32 bits; as such, using this amount for each pixel can allow optimizations. Beyond truecolor In the late 1990's, some high-end graphics hardware and scanners, such as from SGI, started to use more than 8 bits per channel, such as 12 or 16. This has never become common, as the gain in color resolution is almost invisible – 10 bits per channel seem to be enough to reach the absolute limits of human vision under almost all circumstances. However, professional-quality image manipulation software has started to employ 16 bits per color channel for internal storage, providing protection against accumulating rounding errors when multiple consecutive manipulations are performed on a picture. For extended dynamic range imaging, including high dynamic range imaging (HDRI), floating point numbers are used to describe numbers in excess of 'full' white and black. This allows an image to describe accurately the intensity of the sun and deep shadows in the same colour space. Various models are used to describe these ranges, many employing 32 bit accuracy per channel. A new format is the ILM "half" using 16-bit floating point numbers, it appears this is a much better use of 16 bits than using 16-bit integers and is likely to replace it entirely as hardware becomes fast enough to support it. BrilliantColor 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 technoogies 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. The ATI FireGL V7350 graphics card supports 40-bit and 64-bit color•. Selection of color depth In graphics intensive applications such as computer games, a tradeoff of performance and quality can be achieved by raising or lowering the color depth of the display; graphics with lower color depths do not require as much frame buffer memory or display bandwidth, allowing them to be generated and displayed more quickly. Increasing color depth results in higher color quality at the expense of display speed and responsiveness. See also | ||||||||||
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