The dashed black curve behind the red curve is a standard γ = 2.2 power-law curve, for comparison. Below a compressed value of 0.04045 or a linear intensity of 0.00313, the curve is linear (encoded value proportional to intensity), so γ = 1. The sRGB color space standard used with most cameras, PCs, and printers does not use a simple power-law nonlinearity as above, but has a decoding gamma value near 2.2 over much of its range, as shown in the plot to the right. The system can optionally further manage both cases, through color management, if a better match to the output device gamma is required. In any case, binary data in still image files (such as JPEG) are explicitly encoded (that is, they carry gamma-encoded values, not linear intensities), as are motion picture files (such as MPEG). A notable exception, until the release of Mac OS X 10.6 (Snow Leopard) in September 2009, were Macintosh computers, which encoded with a gamma of 0.55 and decoded with a gamma of 1.8.

In most computer display systems, images are encoded with a gamma of about 0.45 and decoded with the reciprocal gamma of 2.2. The local gamma rises from 1 to about 2.2. Plot of the sRGB standard gamma-expansion nonlinearity in red, and its local gamma value (slope in log–log space) in blue. For a power-law curve, this slope is constant, but the idea can be extended to any type of curve, in which case gamma (strictly speaking, 'point gamma' ) is defined as the slope of the curve in any particular region. That is, gamma can be visualized as the slope of the input–output curve when plotted on logarithmic axes. Gamma correction is, in the simplest cases, defined by the following power-law expression: Gamma correction or gamma is a nonlinear operation used to encode and decode luminance or tristimulus values in video or still image systems. The effect of gamma correction on an image: The original image was taken to varying powers, showing that powers larger than 1 make the shadows darker, while powers smaller than 1 make dark regions lighter.

How to increase gamma