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Truecolor
From Wikipedia, the free encyclopedia
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8-bit color |
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- See also True Colors (disambiguation).
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. By this definition Truecolor is when an image is colored by at least 256 shades of red, green and blue for a total of 16,777,216 color variations.
Truecolor can also refer to a display mode that does not need a Color Look-Up Table (CLUT). This definition of truecolor is relevant for computer graphics, where colors are represented by numbers. If the number is equivalent with the color that is to be displayed, then it is a true color. If the number is an index into a palette or any other method of representing color, then it is not a true color.
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For each pixel, generally one byte is used for each channel with the fourth byte (if present) being used either as an alpha channel data or simply ignored. Byte order is usually either RGB or BGR. However, systems do exist with more than 8 bits per channel, and these are often also referred to as truecolor (for example a 48-bit truecolor scanner).
One byte (eight bits) per channel permits 256 (28) intensities for each of the color channels. This allows 16,777,216 colors for each pixel (often approximated as 16 million despite the fact that it is closer to 17 million). The human eye is popularly believed to be capable of discriminating between as many as ten million colors.[1]
Thirty-two bit truecolor can hold an alpha channel, which given the pixel's degree of transparency (versus opaqueness) for representing translucent images (and is often a requirement for hardware acceleration of such drawing) allowing desktop environments to more easily provide effects such as translucent windows, fading menus, and shadows.
In a framebuffer, an alpha channel is meaningless, but 32-bit truecolor is often used because it makes pixel addressing easier. Addressing an array of 24-bit pixels requires multiplication by three, which is more computationally expensive than multiplication by four, which can be computed by bit shifting.
While the above explanation is more or less from a Microsoft point-of-view (as Windows is the most common desktop operating system and it refers to the 24-bit per pixel color mode as truecolor), truecolor can also refer to a display mode that does not need a Color Look-Up Table (CLUT). Thus, truecolor can be used with any color depth (e.g. 8-bit, 16-bit, 24-bit...) but only without a CLUT. In practice, truecolor in this meaning of the term is usually employed with 15 or more bits of color depth, while color depths of 8 bits or less usually do employ a Color Look-Up Table.
- ^ (1975) Color in Business, Science and Industry, third edition, Wiley Series in Pure and Applied Optics, New York: Wiley-Interscience, p. 388.