Editing Gamma correction (section)

==Methods to perform display gamma correction in computing==
Up to four elements can be manipulated in order to achieve gamma encoding to correct the image to be shown on a typical 2.2- or 1.8-gamma computer display:
* The pixel's intensity values in a given image file; that is, the binary pixel values are stored in the file in such way that they represent the light intensity via gamma-compressed values instead of a linear encoding. This is done systematically with digital video files (as those in a [[DVD]] movie), in order to minimize the gamma-decoding step while playing, and maximize image quality for the given storage. Similarly, pixel values in standard image file formats are usually gamma-compensated, either for sRGB gamma (or equivalent, an approximation of typical of legacy monitor gammas), or according to some gamma specified by metadata such as an [[ICC profile]]. If the encoding gamma does not match the reproduction system's gamma, further correction may be done, either on display or to create a modified image file with a different profile.
* The rendering software writes gamma-encoded pixel binary values directly to the video memory (when [[highcolor]]/[[24-bit color|truecolor]] modes are used) or in the [[CLUT]] [[hardware register]]s (when [[indexed color]] modes are used) of the [[display adapter]]. They drive [[digital-to-analog converter]]s (DAC) which output the proportional voltages to the display. For example, when using [[List of monochrome and RGB color formats#24-bit RGB|24-bit RGB]] color (8 bits per channel), writing a value of 128 (rounded midpoint of the 0–255 [[byte]] range) in video memory it outputs the proportional {{nowrap|≈ 0.5}} voltage to the display, which it is shown darker due to the monitor behavior. Alternatively, to achieve {{nowrap|≈ 50%}} intensity, a gamma-encoded [[look-up table]] can be applied to write a value near to 187 instead of 128 by the rendering software.
* Modern display adapters have dedicated calibrating CLUTs, which can be loaded once with the appropriate gamma-correction [[look-up table]] in order to modify the encoded signals digitally before the DACs that output voltages to the monitor.<ref>[http://msdn2.microsoft.com/en-us/library/ms536529.aspx ''SetDeviceGammaRamp'', the Win32 API to download arbitrary gamma ramps to display hardware]</ref> Setting up these tables to be correct is called ''hardware calibration''.<ref name=cm>[http://ftp2.bmtmicro.com/dlc/Color%20Management.pdf Jonathan Sachs (2003). Color Management. Digital Light & Color.] {{webarchive|url=https://web.archive.org/web/20080704074540/http://ftp2.bmtmicro.com/dlc/Color%20Management.pdf |date=2008-07-04 }}</ref>
* Some modern monitors allow the user to manipulate their gamma behavior (as if it were merely another brightness/contrast-like setting), encoding the input signals by themselves before they are displayed on screen. This is also a ''calibration by hardware'' technique but it is performed on the analog electric signals instead of remapping the digital values, as in the previous cases.

In a correctly calibrated system, each component will have a specified gamma for its input and/or output encodings.<ref name=cm/> Stages may change the gamma to correct for different requirements, and finally the output device will do gamma decoding or correction as needed, to get to a linear intensity domain. All the encoding and correction methods can be arbitrarily superimposed, without mutual knowledge of this fact among the different elements; if done incorrectly, these conversions can lead to highly distorted results, but if done correctly as dictated by standards and conventions will lead to a properly functioning system.

In a typical system, for example from camera through [[JPEG]] file to display, the role of gamma correction will involve several cooperating parts. The camera encodes its rendered image into the JPEG file using one of the standard gamma values such as 2.2, for storage and transmission. The display computer may use a [[color management]] engine to convert to a different color space (such as older Macintosh's {{nowrap|1=''γ'' = 1.8}} color space) before putting pixel values into its video memory. The monitor may do its own gamma correction to match the CRT gamma to that used by the video system. Coordinating the components via standard interfaces with default standard gamma values makes it possible to get such system properly configured.