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Gamma correction or gamma is a nonlinear operation used to encode and decode luminance or tristimulus values in video or still image systems. [1] Gamma correction is, in the simplest cases, defined by the following power-law expression: =,
These three results coincide with gamma correction of the bottom layer with γ=2 (for top black), unchanged bottom layer (or, what is the same, γ=1; for top neutral gray), and γ=0.5 (for top white). The formula used by Photoshop as of 2012 has a discontinuity of local contrast, and other formulas correct it. Photoshop's formula is: [6]
Gamma correction is particularly useful for bringing details that would be hard to see on most computer monitors out of shadows. In some image editing software, this is called "curves", usually, a tool found in the color menu, and no reference to "gamma" is used anywhere in the program or the program documentation.
Because HSL and HSV are simple transformations of device-dependent RGB models, the physical colors they define depend on the colors of the red, green, and blue primaries of the device or of the particular RGB space, and on the gamma correction used to represent the amounts of those primaries. Each unique RGB device therefore has unique HSL and ...
The presence of gamma encoding is denoted with the prime symbol ′. Gamma-correcting electro-optical transfer functions (EOTF) are used due to the nonlinear response of human vision. The use of gamma improves perceived signal-to-noise in analogue systems, and allows for more efficient data encoding in digital systems.
Interpolation and Gamma Correction In most real-world systems, gamma correction is required to linearize the response curve of the sensor and display systems. If this is not taken into account, the resultant non-linear distortion will defeat the purpose of anti-aliasing calculations based on the assumption of a linear system response.
On a typical standard 2.2-gamma CRT display, an input intensity RGB value of (0.5, 0.5, 0.5) only outputs about 22% of full brightness (1.0, 1.0, 1.0), instead of 50%. [19] To obtain the correct response, a gamma correction is used in encoding the image data, and possibly further corrections as part of the color calibration process of the device.
They are not completely representative of how they look on TV displays, since these follow the ITU-R BT.1886 standard, specifying a different gamma correction value, and thus colors below will look darker on such a display, and those darker colors will be the reference ones. The off-by-one errors (for example 254 instead of 255 and 1 instead of ...