Gamma Adjust

This command lets you convert a black and white or color image from one gamma value to another. Increasing the gamma makes the image darker increases its contrast. Decreasing the gamma makes it lighter and reduces contrast. The effect is stronger in the darker tones of the image.

For video and monitor display, gamma 2.2 is the standard. For pre-press work, a gamma value of 1.8 is normally used to more accurately represent the limited contrast range of printing presses. A gamma value of 1.0 corresponds to so-called linear gamma where the brightness of the image is proportional to the pixel values.

Amount

The amount control lets you control how much of the gamma adjust transformation is applied to the input image. You can apply a percentage of the transformation to the entire image, or you can specify an amount mask to restrict the effects of the transformation to only part of the input image.

Channel(s)

This lets you select the color space to use when adjusting gamma

HSV -- The HSV brightness channel is adjusted.

HSL -- The HSL brightness channel is adjusted.

RGB -- The R, G and B channels are adjusted independently with a slider for each one.

Gamma factor

This slider control applies a multiplier to the input image gamma and thus lets you either increase or decrease the gamma.