Documentation/userspace-api/media/v4l/colorspaces-details.rst

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Documentation/userspace-api/media/v4l/colorspaces-details.rst
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Repository support layer: documentation, build tooling, samples, user-space helper tools, generated initramfs support, licenses, and validation utilities.

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.. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later
.. c:namespace:: V4L

********************************
Detailed Colorspace Descriptions
********************************


.. _col-smpte-170m:

Colorspace SMPTE 170M (V4L2_COLORSPACE_SMPTE170M)
=================================================

The :ref:`smpte170m` standard defines the colorspace used by NTSC and
PAL and by SDTV in general. The default transfer function is
``V4L2_XFER_FUNC_709``. The default Y'CbCr encoding is
``V4L2_YCBCR_ENC_601``. The default Y'CbCr quantization is limited
range. The chromaticities of the primary colors and the white reference
are:

.. flat-table:: SMPTE 170M Chromaticities
    :header-rows:  1
    :stub-columns: 0
    :widths:       1 1 2

    * - Color
      - x
      - y
    * - Red
      - 0.630
      - 0.340
    * - Green
      - 0.310
      - 0.595
    * - Blue
      - 0.155
      - 0.070
    * - White Reference (D65)
      - 0.3127
      - 0.3290


The red, green and blue chromaticities are also often referred to as the
SMPTE C set, so this colorspace is sometimes called SMPTE C as well.

The transfer function defined for SMPTE 170M is the same as the one
defined in Rec. 709.

.. math::

    L' = -1.099(-L)^{0.45} + 0.099 \text{, for } L \le-0.018

    L' = 4.5L \text{, for } -0.018 < L < 0.018

    L' = 1.099L^{0.45} - 0.099 \text{, for } L \ge 0.018

Inverse Transfer function:

.. math::

    L = -\left( \frac{L' - 0.099}{-1.099} \right) ^{\frac{1}{0.45}} \text{, for } L' \le -0.081

    L = \frac{L'}{4.5} \text{, for } -0.081 < L' < 0.081

    L = \left(\frac{L' + 0.099}{1.099}\right)^{\frac{1}{0.45} } \text{, for } L' \ge 0.081

The luminance (Y') and color difference (Cb and Cr) are obtained with
the following ``V4L2_YCBCR_ENC_601`` encoding:

.. math::

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