Gamma Correction

The luminance intensity generated by most displays is not a linear function of the applied signal but is proportional to some power (referred to as gamma) of the signal voltage. As a result, high intensity ranges are expanded and low intensity ranges are compressed. This nonlinearity must be compensated to achieve correct color reproduction. To do this, luminance of each of the linear red, green, and blue components is reduced to a nonlinear form using an inverse transformation. This process is called "gamma correction".

The Intel IPP functions use the following basic equations to convert an RGB image to a gamma-corrected R'G'B' image:

for R,G,B < 0.018

R' = 4.5R

G' = 4.5G

B' = 4.5B

for R,G,B ≥ 0.018

R' =1.099R^0.45 - 0.099

G' =1.099G^0.45 - 0.099

B' =1.099B^0.45 - 0.099

Note that the channel intensity values are normalized to fit in the range [0..1]. The gamma value is equal to 1/0.45 = 2.22 in conformity with ITU Rec.709 specification (see [ITU709]).