Gamma Correction
Gamma correction of images is used to optimize the
usage of data type depth when encoding an image by taking advantage of the
non-linear manner in which humans perceive light and color. This non-linearity
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
non-linear 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]
).