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Information about Highcolor

Color depth
8-bit color
15/16 bit: Highcolor
24/32 bit: Truecolor
Web-safe color
Related
RGB color model
Palette
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Highcolour graphics (variously spelled Hicolour, Highcolor, and Hicolor, and known as Thousands of colors on a Macintosh) is a method of storing image information in a computer's memory such that each pixel is represented by two bytes. Usually the colour is represented by all 16 bits, but some video chipsets also support 15 bit highcolour.

15-bit highcolour

In 15 bit highcolour, one of the bits of the two bytes is ignored, and the remaining 15 bits are split between the red, green, and blue components of the final colour, like this:

Bit15141312111009080706050403020100 ! Data | x || R || R || R || R || R || G || G || G || G || G || B || B || B || B || B


Each of the RGB components has 5 bits associated, giving 2^5 = 32 intensities of each component. This allows 32,768 possible colours for each pixel.

The popular Cirrus Logic graphics chips of the early 1990s made use of the spare high-order bit for their so-called "mixed" video modes: with bit 15 clear, bits 0 through 14 would be treated as an RGB value as described above, while with bit 15 set, bit 0 through 7 would be interpreted as an index into a 256-color palette. This would have enabled display of (comparatively) high-quality color images side by side with palette-animated screen elements, but in practice, this feature was hardly used by any software.

16-bit highcolour

Human eyes are more sensitive to green light. The greens are easier to see than the reds, and the blues are almost impossible to see.


When all 16 bits are used, one of the components (usually green, see below) gets an extra bit, allowing 64 levels of intensity for that component, and a total of 65,536 available colours. This can lead to small discrepancies in encoding, when e.g. we wish to encode the 24-bit colour RGB (40, 40, 40) with 16 bits (a problem common to subsampling). Forty in binary is 00101000. The red and blue channels will take the five most significant bits, and will have a value of 00101, or 5 on a scale from 0 to 31 (16.1%). The green channel, with six bits of precision, will have a binary value of 001010, or 10 on a scale from 0 to 63 (15.9%). Because of this, the colour RGB (40, 40, 40) will have a slight green tinge when displayed in 16 bits. Note that 40 on a scale from 0 to 255 is 15.7%.

Green is usually chosen for the extra bit in 16 bits because the human eye has its highest sensitivity for green shades. For a demonstration, look closely at the following picture (note: this will work only on monitors displaying truecolour, i.e., 24 or 32 bits) where dark shades of red, green and blue are shown using 128 levels of intensities for each component (7 bits). Readers with normal vision should see the shades of green relatively easily, while the shades of red should be difficult to see, and the shades of blue are likely indistinguishable. More rarely, some systems support having the extra bit of colour depth on the red or blue channel, usually in applications where that colour is more prevalent (photographing of skin tones or skies, for example).

Other notes

Unlike planar or chunky (packed pixel) graphics, there is generally no need for a colour look up table (CLUT, or palette) when in Highcolour mode, because there are enough available colours per pixel to represent graphics and photos reasonably satisfactorily, although the lack of precision has an impact on image fidelity. As a result, some image formats (e.g., TIF) can save paletted 16-bit images with an embedded CLUT.

See also

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.
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8-bit color graphics is a method of storing image information in a computer's memory or in an image file, such that each pixel is represented by one 8-bit byte. The maximum number of colors that can be displayed at any one time is 256.
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Truecolor is a method of representing and storing graphical image information (especially in computer processing) such that a very large number of colors, shades, and hues can be displayed at once, such as high quality photographic images or complex graphics.
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RGB color model is an additive model in which red, green, and blue (often used in additive light models) are combined in various ways to reproduce other colors. The name of the model and the abbreviation ‘RGB’ come from the three primary colors, red, green, and blue and
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palette, in computer graphics, is a designated subset of the total range of colors supported by a computer graphics system. Each color in the palette is assigned a number, and for each pixel, one of these numbers is stored. This number determines the color of the pixel.
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Macintosh, commonly known as Mac, is a brand name which covers several lines of personal computers designed, developed, and marketed by Apple Inc. Named after the McIntosh variety of apple, the original Macintosh was released on January 24, 1984.
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computer is a machine which manipulates data according to a list of instructions.

Computers take numerous physical forms. The first devices that resemble modern computers date to the mid-20th century (around 1940 - 1941), although the computer concept and various machines
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pixel (short for picture element, using the common abbreviation "pix" for "pictures") is a single point in a graphic image. Each such information element is not really a dot, nor a square, but an abstract sample.
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byte (pronounced /baɪt/) is a unit of measurement of information storage, most often consisting of eight bits. In many computer architectures it is a unit of memory addressing.
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Color or colour[1] (see spelling differences) is the visual perceptual property corresponding in humans to the categories called red, yellow, blue, black, etc.
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BIT is an acronym for:
  • Bannari amman Institute of Technology
  • Bangalore Institute of Technology
  • Beijing Institute of Technology
  • Benzisothiazolinone
  • Bilateral Investment Treaty
  • Bhilai Institute of Technology - Durg

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Red is any of a number of similar colors evoked by light consisting predominantly of the longest wavelengths of light discernible by the human eye, in the wavelength range of roughly 625–750 nm.
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Green is a color, the perception of which is evoked by light having a spectrum dominated by energy with a wavelength of roughly 520–570 nm. It is considered one of the additive primary colors.
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The term blue may refer to any of a number of similar colours. The sensation of blue is made by light having a spectrum dominated by energy in the wavelength range of about 440–490 nm.
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Cirrus Logic (NASDAQ:  CRUS ) is a fabless semiconductor supplier specializing in analog, mixed-signal, and DSP chips. They are presently headquartered in Austin, Texas. Their audio-processors are found in many home-theater receiver and other set-top box hardware.
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Color cycling, also known as palette shifting, is a technique used in computer graphics in which colors are changed in order to give the impression of animation. This technique was mainly used in early computer games, as storing one image and changing its palette required
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RGB color model is an additive model in which red, green, and blue (often used in additive light models) are combined in various ways to reproduce other colors. The name of the model and the abbreviation ‘RGB’ come from the three primary colors, red, green, and blue and
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For the signal processing technique, see .
In computer graphics, subsampling (or "downsampling") is the process of reducing an image to a smaller size.
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Truecolor is a method of representing and storing graphical image information (especially in computer processing) such that a very large number of colors, shades, and hues can be displayed at once, such as high quality photographic images or complex graphics.
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In computer graphics, planar is method of representing pixel information with several bitplanes. There are also cases where byteplanes have been used. Each individual bit in a bitplane is related to a single pixel on the screen.
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In packed pixel or chunky frame buffer organization, the bits defining each pixel are grouped together. For example, if there are 4-bits per pixel (16 colors), each frame buffer byte defines two pixels.

See also

  • Highcolor
  • Planar
  • Truecolor

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A Colour Look-Up Table (CLUT) is a device which converts the logical colour numbers stored in each pixel of video memory into physical colours, normally represented as RGB triplets, that can be displayed on a computer monitor.
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In computer graphics, planar is method of representing pixel information with several bitplanes. There are also cases where byteplanes have been used. Each individual bit in a bitplane is related to a single pixel on the screen.
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In packed pixel or chunky frame buffer organization, the bits defining each pixel are grouped together. For example, if there are 4-bits per pixel (16 colors), each frame buffer byte defines two pixels.

See also

  • Highcolor
  • Planar
  • Truecolor

..... Click the link for more information.
Truecolor is a method of representing and storing graphical image information (especially in computer processing) such that a very large number of colors, shades, and hues can be displayed at once, such as high quality photographic images or complex graphics.
..... Click the link for more information.
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.
..... Click the link for more information.


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