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Below are the details on these options.

Linear

The floating point number is taken as is, without any additional transformations.

Parameters: none.

Gamma

The floating point number is subjected to gamma transformation. Pixels with brightness below the Black Point are interpreted as pure black, those with brightness above the White Point are interpreted as pure white, and those in between are converted using the power law with exponent Gamma.

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If Autocontrast option is selected, then White Point and Black Point are calculated automatically.

Gamma+Contrast

The floating point number is subjected to the following two transformations in a row:

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Parameters: Gamma, Offset, ContrastShift.

Gamma+Curves

The floating point number is subjected to the following two transformations in a row:

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Parameters: Gamma, Offset, ShadowShift, MidtoneShift, HighlightShift.

GAMMA+CLAHE

CLAHE algorithm (Contrast Limited Adaptive Histogram Equalization) splits the image into several regions (Region Size along each side) and applies the histogram equalization transformation to each region. Then an overall Gamma transformation (see above) is applied.

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