.. SPDX-FileCopyrightText: 2021 Intel Corporation
..
.. SPDX-License-Identifier: CC-BY-4.0

.. _gamma-correction:

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 oneIPL 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' = 1.099R0.45 - 0.099``


``G' = 1.099G0.45 - 0.099``


``B' = 1.099B0.45 - 0.099``


.. note::

    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
    :ref:`[ITU709] <bibliography-table>`).