Color depth
The number of bits of resolved intensity in a color channel is also known as radiometric resolution, especially in the context of satellite images.
Old graphics chips, particularly those used in home computers and video game consoles, often have the ability to use a different palette per sprites and tiles in order to increase the maximum number of simultaneously displayed colors, while minimizing use of then-expensive memory (and bandwidth).
For example, in the ZX Spectrum the picture is stored in a two-color format, but these two colors can be separately defined for each rectangular block of 8×8 pixels.
In the late 1980s there were professional displays with resolutions up to 300 dpi (the same as a contemporary laser printer) but color proved more popular.
Gray-scale early NeXTstation, color Macintoshes, Atari ST medium resolution.
Many early home computers with TV displays, including the ZX Spectrum and BBC Micro.
RGBA4444, a related 16 bpp representation providing the color cube and 16 levels of transparency, is a common texture format in mobile graphics.
However, an alternate assignment which reassigns the unused bit to the G channel allows 65,536 colors to be represented, but without transparency.
As of 2018, 24-bit color depth is used by virtually every computer and phone display [citation needed] and the vast majority of image storage formats.
Some SGI systems had 10- (or more) bit digital-to-analog converters for the video signal and could be set up to interpret data stored this way for display.
An early example was the Radius ThunderPower card for the Macintosh, which included extensions for QuickDraw and Adobe Photoshop plugins to support editing 30-bit images.
[24][25] The ATI FireGL V7350 graphics card supports 40- and 64-bit pixels (30 and 48 bit color depth with an alpha channel).
[28][29] High Efficiency Video Coding (HEVC or H.265) defines the Main 10 profile, which allows for 8 or 10 bits per sample with 4:2:0 chroma subsampling.
Numbers greater than 1 were for colors brighter than the display could show, as in high-dynamic-range imaging (HDRI).
Floating point numbers can represent linear light levels spacing the samples semi-logarithmically.
Floating point representations also allow for drastically larger dynamic ranges as well as negative values.
In 1999, Industrial Light & Magic released the open standard image file format OpenEXR which supported 16-bit-per-channel half-precision floating-point numbers.
For storing and manipulating images, alternative ways of expanding the traditional triangle exist: One can convert image coding to use fictitious primaries, that are not physically possible but that have the effect of extending the triangle to enclose a much larger color gamut.
Recent technologies such as Texas Instruments's BrilliantColor augment the typical red, green, and blue channels with up to three other primaries: cyan, magenta, and yellow.
[citation needed] The Sharp Aquos line of televisions has introduced Quattron technology, which augments the usual RGB pixel components with a yellow subpixel.
[citation needed] Because humans are overwhelmingly trichromats or dichromats[b] one might suppose that adding a fourth "primary" color could provide no practical benefit.
The deficit of colors is particularly noticeable in saturated shades of bluish green (shown as the left upper grey part of the horseshoe in the diagram) of RGB displays: Most humans can see more vivid blue-greens than any color video screen can display.
