mirror of https://gitee.com/openkylin/linux.git
745 lines
18 KiB
ReStructuredText
745 lines
18 KiB
ReStructuredText
.. -*- coding: utf-8; mode: rst -*-
|
|
|
|
********************************
|
|
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:
|
|
|
|
|
|
|
|
.. tabularcolumns:: |p{4.4cm}|p{4.4cm}|p{8.7cm}|
|
|
|
|
.. 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::
|
|
|
|
Y' = 0.2990R' + 0.5870G' + 0.1140B'
|
|
|
|
Cb = -0.1687R' - 0.3313G' + 0.5B'
|
|
|
|
Cr = 0.5R' - 0.4187G' - 0.0813B'
|
|
|
|
Y' is clamped to the range [0…1] and Cb and Cr are clamped to the range
|
|
[-0.5…0.5]. This conversion to Y'CbCr is identical to the one defined in
|
|
the :ref:`itu601` standard and this colorspace is sometimes called
|
|
BT.601 as well, even though BT.601 does not mention any color primaries.
|
|
|
|
The default quantization is limited range, but full range is possible
|
|
although rarely seen.
|
|
|
|
|
|
.. _col-rec709:
|
|
|
|
Colorspace Rec. 709 (V4L2_COLORSPACE_REC709)
|
|
============================================
|
|
|
|
The :ref:`itu709` standard defines the colorspace used by HDTV in
|
|
general. The default transfer function is ``V4L2_XFER_FUNC_709``. The
|
|
default Y'CbCr encoding is ``V4L2_YCBCR_ENC_709``. The default Y'CbCr
|
|
quantization is limited range. The chromaticities of the primary colors
|
|
and the white reference are:
|
|
|
|
|
|
|
|
.. tabularcolumns:: |p{4.4cm}|p{4.4cm}|p{8.7cm}|
|
|
|
|
.. flat-table:: Rec. 709 Chromaticities
|
|
:header-rows: 1
|
|
:stub-columns: 0
|
|
:widths: 1 1 2
|
|
|
|
* - Color
|
|
- x
|
|
- y
|
|
* - Red
|
|
- 0.640
|
|
- 0.330
|
|
* - Green
|
|
- 0.300
|
|
- 0.600
|
|
* - Blue
|
|
- 0.150
|
|
- 0.060
|
|
* - White Reference (D65)
|
|
- 0.3127
|
|
- 0.3290
|
|
|
|
|
|
The full name of this standard is Rec. ITU-R BT.709-5.
|
|
|
|
Transfer function. Normally L is in the range [0…1], but for the
|
|
extended gamut xvYCC encoding values outside that range are allowed.
|
|
|
|
.. 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_709`` encoding:
|
|
|
|
.. math::
|
|
|
|
Y' = 0.2126R' + 0.7152G' + 0.0722B'
|
|
|
|
Cb = -0.1146R' - 0.3854G' + 0.5B'
|
|
|
|
Cr = 0.5R' - 0.4542G' - 0.0458B'
|
|
|
|
Y' is clamped to the range [0…1] and Cb and Cr are clamped to the range
|
|
[-0.5…0.5].
|
|
|
|
The default quantization is limited range, but full range is possible
|
|
although rarely seen.
|
|
|
|
The ``V4L2_YCBCR_ENC_709`` encoding described above is the default for
|
|
this colorspace, but it can be overridden with ``V4L2_YCBCR_ENC_601``,
|
|
in which case the BT.601 Y'CbCr encoding is used.
|
|
|
|
Two additional extended gamut Y'CbCr encodings are also possible with
|
|
this colorspace:
|
|
|
|
The xvYCC 709 encoding (``V4L2_YCBCR_ENC_XV709``, :ref:`xvycc`) is
|
|
similar to the Rec. 709 encoding, but it allows for R', G' and B' values
|
|
that are outside the range [0…1]. The resulting Y', Cb and Cr values are
|
|
scaled and offset:
|
|
|
|
.. math::
|
|
|
|
Y' = \frac{219}{256} * (0.2126R' + 0.7152G' + 0.0722B') + \frac{16}{256}
|
|
|
|
Cb = \frac{224}{256} * (-0.1146R' - 0.3854G' + 0.5B')
|
|
|
|
Cr = \frac{224}{256} * (0.5R' - 0.4542G' - 0.0458B')
|
|
|
|
The xvYCC 601 encoding (``V4L2_YCBCR_ENC_XV601``, :ref:`xvycc`) is
|
|
similar to the BT.601 encoding, but it allows for R', G' and B' values
|
|
that are outside the range [0…1]. The resulting Y', Cb and Cr values are
|
|
scaled and offset:
|
|
|
|
.. math::
|
|
|
|
Y' = \frac{219}{256} * (0.2990R' + 0.5870G' + 0.1140B') + \frac{16}{256}
|
|
|
|
Cb = \frac{224}{256} * (-0.1687R' - 0.3313G' + 0.5B')
|
|
|
|
Cr = \frac{224}{256} * (0.5R' - 0.4187G' - 0.0813B')
|
|
|
|
Y' is clamped to the range [0…1] and Cb and Cr are clamped to the range
|
|
[-0.5…0.5]. The non-standard xvYCC 709 or xvYCC 601 encodings can be
|
|
used by selecting ``V4L2_YCBCR_ENC_XV709`` or ``V4L2_YCBCR_ENC_XV601``.
|
|
The xvYCC encodings always use full range quantization.
|
|
|
|
|
|
.. _col-srgb:
|
|
|
|
Colorspace sRGB (V4L2_COLORSPACE_SRGB)
|
|
======================================
|
|
|
|
The :ref:`srgb` standard defines the colorspace used by most webcams
|
|
and computer graphics. The default transfer function is
|
|
``V4L2_XFER_FUNC_SRGB``. The default Y'CbCr encoding is
|
|
``V4L2_YCBCR_ENC_601``. The default Y'CbCr quantization is full range.
|
|
The chromaticities of the primary colors and the white reference are:
|
|
|
|
|
|
|
|
.. tabularcolumns:: |p{4.4cm}|p{4.4cm}|p{8.7cm}|
|
|
|
|
.. flat-table:: sRGB Chromaticities
|
|
:header-rows: 1
|
|
:stub-columns: 0
|
|
:widths: 1 1 2
|
|
|
|
* - Color
|
|
- x
|
|
- y
|
|
* - Red
|
|
- 0.640
|
|
- 0.330
|
|
* - Green
|
|
- 0.300
|
|
- 0.600
|
|
* - Blue
|
|
- 0.150
|
|
- 0.060
|
|
* - White Reference (D65)
|
|
- 0.3127
|
|
- 0.3290
|
|
|
|
|
|
These chromaticities are identical to the Rec. 709 colorspace.
|
|
|
|
Transfer function. Note that negative values for L are only used by the
|
|
Y'CbCr conversion.
|
|
|
|
.. math::
|
|
|
|
L' = -1.055(-L)^{\frac{1}{2.4} } + 0.055\text{, for }L < -0.0031308
|
|
|
|
L' = 12.92L\text{, for }-0.0031308 \le L \le 0.0031308
|
|
|
|
L' = 1.055L ^{\frac{1}{2.4} } - 0.055\text{, for }0.0031308 < L \le 1
|
|
|
|
Inverse Transfer function:
|
|
|
|
.. math::
|
|
|
|
L = -((-L' + 0.055) / 1.055) ^{2.4}\text{, for }L' < -0.04045
|
|
|
|
L = L' / 12.92\text{, for }-0.04045 \le L' \le 0.04045
|
|
|
|
L = ((L' + 0.055) / 1.055) ^{2.4}\text{, for }L' > 0.04045
|
|
|
|
The luminance (Y') and color difference (Cb and Cr) are obtained with
|
|
the following ``V4L2_YCBCR_ENC_601`` encoding as defined by :ref:`sycc`:
|
|
|
|
.. math::
|
|
|
|
Y' = 0.2990R' + 0.5870G' + 0.1140B'
|
|
|
|
Cb = -0.1687R' - 0.3313G' + 0.5B'
|
|
|
|
Cr = 0.5R' - 0.4187G' - 0.0813B'
|
|
|
|
Y' is clamped to the range [0…1] and Cb and Cr are clamped to the range
|
|
[-0.5…0.5]. This transform is identical to one defined in SMPTE
|
|
170M/BT.601. The Y'CbCr quantization is full range.
|
|
|
|
|
|
.. _col-adobergb:
|
|
|
|
Colorspace Adobe RGB (V4L2_COLORSPACE_ADOBERGB)
|
|
===============================================
|
|
|
|
The :ref:`adobergb` standard defines the colorspace used by computer
|
|
graphics that use the AdobeRGB colorspace. This is also known as the
|
|
:ref:`oprgb` standard. The default transfer function is
|
|
``V4L2_XFER_FUNC_ADOBERGB``. The default Y'CbCr encoding is
|
|
``V4L2_YCBCR_ENC_601``. The default Y'CbCr quantization is full
|
|
range. The chromaticities of the primary colors and the white reference
|
|
are:
|
|
|
|
|
|
|
|
.. tabularcolumns:: |p{4.4cm}|p{4.4cm}|p{8.7cm}|
|
|
|
|
.. flat-table:: Adobe RGB Chromaticities
|
|
:header-rows: 1
|
|
:stub-columns: 0
|
|
:widths: 1 1 2
|
|
|
|
* - Color
|
|
- x
|
|
- y
|
|
* - Red
|
|
- 0.6400
|
|
- 0.3300
|
|
* - Green
|
|
- 0.2100
|
|
- 0.7100
|
|
* - Blue
|
|
- 0.1500
|
|
- 0.0600
|
|
* - White Reference (D65)
|
|
- 0.3127
|
|
- 0.3290
|
|
|
|
|
|
|
|
Transfer function:
|
|
|
|
.. math::
|
|
|
|
L' = L ^{\frac{1}{2.19921875}}
|
|
|
|
Inverse Transfer function:
|
|
|
|
.. math::
|
|
|
|
L = L'^{(2.19921875)}
|
|
|
|
The luminance (Y') and color difference (Cb and Cr) are obtained with
|
|
the following ``V4L2_YCBCR_ENC_601`` encoding:
|
|
|
|
.. math::
|
|
|
|
Y' = 0.2990R' + 0.5870G' + 0.1140B'
|
|
|
|
Cb = -0.1687R' - 0.3313G' + 0.5B'
|
|
|
|
Cr = 0.5R' - 0.4187G' - 0.0813B'
|
|
|
|
Y' is clamped to the range [0…1] and Cb and Cr are clamped to the range
|
|
[-0.5…0.5]. This transform is identical to one defined in SMPTE
|
|
170M/BT.601. The Y'CbCr quantization is full range.
|
|
|
|
|
|
.. _col-bt2020:
|
|
|
|
Colorspace BT.2020 (V4L2_COLORSPACE_BT2020)
|
|
===========================================
|
|
|
|
The :ref:`itu2020` standard defines the colorspace used by Ultra-high
|
|
definition television (UHDTV). The default transfer function is
|
|
``V4L2_XFER_FUNC_709``. The default Y'CbCr encoding is
|
|
``V4L2_YCBCR_ENC_BT2020``. The default R'G'B' quantization is limited
|
|
range (!), and so is the default Y'CbCr quantization. The chromaticities
|
|
of the primary colors and the white reference are:
|
|
|
|
|
|
|
|
.. tabularcolumns:: |p{4.4cm}|p{4.4cm}|p{8.7cm}|
|
|
|
|
.. flat-table:: BT.2020 Chromaticities
|
|
:header-rows: 1
|
|
:stub-columns: 0
|
|
:widths: 1 1 2
|
|
|
|
* - Color
|
|
- x
|
|
- y
|
|
* - Red
|
|
- 0.708
|
|
- 0.292
|
|
* - Green
|
|
- 0.170
|
|
- 0.797
|
|
* - Blue
|
|
- 0.131
|
|
- 0.046
|
|
* - White Reference (D65)
|
|
- 0.3127
|
|
- 0.3290
|
|
|
|
|
|
|
|
Transfer function (same as Rec. 709):
|
|
|
|
.. math::
|
|
|
|
L' = 4.5L\text{, for }0 \le L < 0.018
|
|
|
|
L' = 1.099L ^{0.45} - 0.099\text{, for } 0.018 \le L \le 1
|
|
|
|
Inverse Transfer function:
|
|
|
|
.. math::
|
|
|
|
L = L' / 4.5\text{, for } 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_BT2020`` encoding:
|
|
|
|
.. math::
|
|
|
|
Y' = 0.2627R' + 0.6780G' + 0.0593B'
|
|
|
|
Cb = -0.1396R' - 0.3604G' + 0.5B'
|
|
|
|
Cr = 0.5R' - 0.4598G' - 0.0402B'
|
|
|
|
Y' is clamped to the range [0…1] and Cb and Cr are clamped to the range
|
|
[-0.5…0.5]. The Y'CbCr quantization is limited range.
|
|
|
|
There is also an alternate constant luminance R'G'B' to Yc'CbcCrc
|
|
(``V4L2_YCBCR_ENC_BT2020_CONST_LUM``) encoding:
|
|
|
|
Luma:
|
|
|
|
.. math::
|
|
:nowrap:
|
|
|
|
\begin{align*}
|
|
Yc' = (0.2627R + 0.6780G + 0.0593B)'& \\
|
|
B' - Yc' \le 0:& \\
|
|
&Cbc = (B' - Yc') / 1.9404 \\
|
|
B' - Yc' > 0: & \\
|
|
&Cbc = (B' - Yc') / 1.5816 \\
|
|
R' - Yc' \le 0:& \\
|
|
&Crc = (R' - Y') / 1.7184 \\
|
|
R' - Yc' > 0:& \\
|
|
&Crc = (R' - Y') / 0.9936
|
|
\end{align*}
|
|
|
|
Yc' is clamped to the range [0…1] and Cbc and Crc are clamped to the
|
|
range [-0.5…0.5]. The Yc'CbcCrc quantization is limited range.
|
|
|
|
|
|
.. _col-dcip3:
|
|
|
|
Colorspace DCI-P3 (V4L2_COLORSPACE_DCI_P3)
|
|
==========================================
|
|
|
|
The :ref:`smpte431` standard defines the colorspace used by cinema
|
|
projectors that use the DCI-P3 colorspace. The default transfer function
|
|
is ``V4L2_XFER_FUNC_DCI_P3``. The default Y'CbCr encoding is
|
|
``V4L2_YCBCR_ENC_709``. The default Y'CbCr quantization is limited range.
|
|
|
|
.. note::
|
|
|
|
Note that this colorspace standard does not specify a
|
|
Y'CbCr encoding since it is not meant to be encoded to Y'CbCr. So this
|
|
default Y'CbCr encoding was picked because it is the HDTV encoding.
|
|
|
|
The chromaticities of the primary colors and the white reference are:
|
|
|
|
|
|
|
|
.. tabularcolumns:: |p{4.4cm}|p{4.4cm}|p{8.7cm}|
|
|
|
|
.. flat-table:: DCI-P3 Chromaticities
|
|
:header-rows: 1
|
|
:stub-columns: 0
|
|
:widths: 1 1 2
|
|
|
|
* - Color
|
|
- x
|
|
- y
|
|
* - Red
|
|
- 0.6800
|
|
- 0.3200
|
|
* - Green
|
|
- 0.2650
|
|
- 0.6900
|
|
* - Blue
|
|
- 0.1500
|
|
- 0.0600
|
|
* - White Reference
|
|
- 0.3140
|
|
- 0.3510
|
|
|
|
|
|
|
|
Transfer function:
|
|
|
|
.. math::
|
|
|
|
L' = L^{\frac{1}{2.6}}
|
|
|
|
Inverse Transfer function:
|
|
|
|
.. math::
|
|
|
|
L = L'^{(2.6)}
|
|
|
|
Y'CbCr encoding is not specified. V4L2 defaults to Rec. 709.
|
|
|
|
|
|
.. _col-smpte-240m:
|
|
|
|
Colorspace SMPTE 240M (V4L2_COLORSPACE_SMPTE240M)
|
|
=================================================
|
|
|
|
The :ref:`smpte240m` standard was an interim standard used during the
|
|
early days of HDTV (1988-1998). It has been superseded by Rec. 709. The
|
|
default transfer function is ``V4L2_XFER_FUNC_SMPTE240M``. The default
|
|
Y'CbCr encoding is ``V4L2_YCBCR_ENC_SMPTE240M``. The default Y'CbCr
|
|
quantization is limited range. The chromaticities of the primary colors
|
|
and the white reference are:
|
|
|
|
|
|
|
|
.. tabularcolumns:: |p{4.4cm}|p{4.4cm}|p{8.7cm}|
|
|
|
|
.. flat-table:: SMPTE 240M 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
|
|
|
|
|
|
These chromaticities are identical to the SMPTE 170M colorspace.
|
|
|
|
Transfer function:
|
|
|
|
.. math::
|
|
|
|
L' = 4L\text{, for } 0 \le L < 0.0228
|
|
|
|
L' = 1.1115L ^{0.45} - 0.1115\text{, for } 0.0228 \le L \le 1
|
|
|
|
Inverse Transfer function:
|
|
|
|
.. math::
|
|
|
|
L = \frac{L'}{4}\text{, for } 0 \le L' < 0.0913
|
|
|
|
L = \left( \frac{L' + 0.1115}{1.1115}\right) ^{\frac{1}{0.45} }\text{, for } L' \ge 0.0913
|
|
|
|
The luminance (Y') and color difference (Cb and Cr) are obtained with
|
|
the following ``V4L2_YCBCR_ENC_SMPTE240M`` encoding:
|
|
|
|
.. math::
|
|
|
|
Y' = 0.2122R' + 0.7013G' + 0.0865B'
|
|
|
|
Cb = -0.1161R' - 0.3839G' + 0.5B'
|
|
|
|
Cr = 0.5R' - 0.4451G' - 0.0549B'
|
|
|
|
Y' is clamped to the range [0…1] and Cb and Cr are clamped to the
|
|
range [-0.5…0.5]. The Y'CbCr quantization is limited range.
|
|
|
|
|
|
.. _col-sysm:
|
|
|
|
Colorspace NTSC 1953 (V4L2_COLORSPACE_470_SYSTEM_M)
|
|
===================================================
|
|
|
|
This standard defines the colorspace used by NTSC in 1953. In practice
|
|
this colorspace is obsolete and SMPTE 170M should be used instead. 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:
|
|
|
|
|
|
|
|
.. tabularcolumns:: |p{4.4cm}|p{4.4cm}|p{8.7cm}|
|
|
|
|
.. flat-table:: NTSC 1953 Chromaticities
|
|
:header-rows: 1
|
|
:stub-columns: 0
|
|
:widths: 1 1 2
|
|
|
|
* - Color
|
|
- x
|
|
- y
|
|
* - Red
|
|
- 0.67
|
|
- 0.33
|
|
* - Green
|
|
- 0.21
|
|
- 0.71
|
|
* - Blue
|
|
- 0.14
|
|
- 0.08
|
|
* - White Reference (C)
|
|
- 0.310
|
|
- 0.316
|
|
|
|
|
|
.. note::
|
|
|
|
This colorspace uses Illuminant C instead of D65 as the white
|
|
reference. To correctly convert an image in this colorspace to another
|
|
that uses D65 you need to apply a chromatic adaptation algorithm such as
|
|
the Bradford method.
|
|
|
|
The transfer function was never properly defined for NTSC 1953. The Rec.
|
|
709 transfer function is recommended in the literature:
|
|
|
|
.. math::
|
|
|
|
L' = 4.5L\text{, for } 0 \le L < 0.018
|
|
|
|
L' = 1.099L ^{0.45} - 0.099\text{, for } 0.018 \le L \le 1
|
|
|
|
Inverse Transfer function:
|
|
|
|
.. math::
|
|
|
|
L = \frac{L'}{4.5} \text{, for } 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::
|
|
|
|
Y' = 0.2990R' + 0.5870G' + 0.1140B'
|
|
|
|
Cb = -0.1687R' - 0.3313G' + 0.5B'
|
|
|
|
Cr = 0.5R' - 0.4187G' - 0.0813B'
|
|
|
|
Y' is clamped to the range [0…1] and Cb and Cr are clamped to the range
|
|
[-0.5…0.5]. The Y'CbCr quantization is limited range. This transform is
|
|
identical to one defined in SMPTE 170M/BT.601.
|
|
|
|
|
|
.. _col-sysbg:
|
|
|
|
Colorspace EBU Tech. 3213 (V4L2_COLORSPACE_470_SYSTEM_BG)
|
|
=========================================================
|
|
|
|
The :ref:`tech3213` standard defines the colorspace used by PAL/SECAM
|
|
in 1975. In practice this colorspace is obsolete and SMPTE 170M should
|
|
be used instead. 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:
|
|
|
|
|
|
|
|
.. tabularcolumns:: |p{4.4cm}|p{4.4cm}|p{8.7cm}|
|
|
|
|
.. flat-table:: EBU Tech. 3213 Chromaticities
|
|
:header-rows: 1
|
|
:stub-columns: 0
|
|
:widths: 1 1 2
|
|
|
|
* - Color
|
|
- x
|
|
- y
|
|
* - Red
|
|
- 0.64
|
|
- 0.33
|
|
* - Green
|
|
- 0.29
|
|
- 0.60
|
|
* - Blue
|
|
- 0.15
|
|
- 0.06
|
|
* - White Reference (D65)
|
|
- 0.3127
|
|
- 0.3290
|
|
|
|
|
|
|
|
The transfer function was never properly defined for this colorspace.
|
|
The Rec. 709 transfer function is recommended in the literature:
|
|
|
|
.. math::
|
|
|
|
L' = 4.5L\text{, for } 0 \le L < 0.018
|
|
|
|
L' = 1.099L ^{0.45} - 0.099\text{, for } 0.018 \le L \le 1
|
|
|
|
Inverse Transfer function:
|
|
|
|
.. math::
|
|
|
|
L = \frac{L'}{4.5} \text{, for } 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::
|
|
|
|
Y' = 0.2990R' + 0.5870G' + 0.1140B'
|
|
|
|
Cb = -0.1687R' - 0.3313G' + 0.5B'
|
|
|
|
Cr = 0.5R' - 0.4187G' - 0.0813B'
|
|
|
|
Y' is clamped to the range [0…1] and Cb and Cr are clamped to the range
|
|
[-0.5…0.5]. The Y'CbCr quantization is limited range. This transform is
|
|
identical to one defined in SMPTE 170M/BT.601.
|
|
|
|
|
|
.. _col-jpeg:
|
|
|
|
Colorspace JPEG (V4L2_COLORSPACE_JPEG)
|
|
======================================
|
|
|
|
This colorspace defines the colorspace used by most (Motion-)JPEG
|
|
formats. The chromaticities of the primary colors and the white
|
|
reference are identical to sRGB. The transfer function use is
|
|
``V4L2_XFER_FUNC_SRGB``. The Y'CbCr encoding is ``V4L2_YCBCR_ENC_601``
|
|
with full range quantization where Y' is scaled to [0…255] and Cb/Cr are
|
|
scaled to [-128…128] and then clipped to [-128…127].
|
|
|
|
.. note::
|
|
|
|
The JPEG standard does not actually store colorspace
|
|
information. So if something other than sRGB is used, then the driver
|
|
will have to set that information explicitly. Effectively
|
|
``V4L2_COLORSPACE_JPEG`` can be considered to be an abbreviation for
|
|
``V4L2_COLORSPACE_SRGB``, ``V4L2_YCBCR_ENC_601`` and
|
|
``V4L2_QUANTIZATION_FULL_RANGE``.
|