Color depth determines how many unique colors or levels of gray can be reproduced in an image. The depth indicates how many bits of data are used to represent an individual color value, or how many are assigned to each component channel, typically red, green, and blue (RGB) in computer video. However, other color models such as CMYK, HSL, and YUV are also professionally used.
Due to past memory limitations, early computer monitors had single 1-bit color depth where the pixel was either on or off (black or white). Early color monitors were limited to 2, 4, or 8-bits per pixel, allowing for up to 4, 16, or 256 shades of gray or individual colors. In 8-bit color displays, an indexed color lookup table (CLUT) would be used to maximize the appearance of a color image by selectively assigning the 256 colors (from a wider range) that were available.
24-bit color monitors (8-bits per channel) allowed for the display of 16,777,216 unique colors to sufficiently display the visible spectrum, so that typical consumer devices do not go beyond this depth. 32-bit color modes actually use 24-bit color, with remaining 8-bits assigned to transparency. However, high-end devices can display a greater color depths known as "deep color", ranging from 30 to 64-bits.
The GIF and PNG image formats can be encoded in up to 8-bit color (with optional 1-bit transparency, without anti-aliasing). However, the PNG format also supports 24-bit color (without transparency), or 32-bit color (with 8-bit transparency, allowing for 256 levels of opacity). The JPEG image format is always encoded in 24-bit color, with now allowance for transparency. The TIFF file format can be losslessly encoded in 32-bit and higher color depths, as well as other color models, such as CMYK.
Early output devices were capped at 8-bits (256 levels of luminosity) per channel, but modern devices, starting with cameras and scanners can go beyond this. The RAW format used in cameras use the maximum color depth available, such as 16-bits per channel. The extra depth allows for more rigorous editing, while minimizing the eventual loss of image data that occurs more visibly in 8-bits per channel images.
- Color Palettes (PDF) by Marc Johnson, Columbia University School of the Arts. 2020.
- The NeXT Generation by M. Keith Thompson, PC Magazine p.161. 1992-05-12.
- Programming the XGA Direct Color Mode by Julio Sanchez, Maria P. Canton, The PC Graphics Handbook. 2013-10-29.
- Color Depth : 15-bit (32,768 colors), MobyGames. Accessed 2020-02-19.