974 строки
20 KiB
ReStructuredText
974 строки
20 KiB
ReStructuredText
.. -*- coding: utf-8; mode: rst -*-
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********************************
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Detailed Colorspace Descriptions
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********************************
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.. _col-smpte-170m:
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Colorspace SMPTE 170M (V4L2_COLORSPACE_SMPTE170M)
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=================================================
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The :ref:`smpte170m` standard defines the colorspace used by NTSC and
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PAL and by SDTV in general. The default transfer function is
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``V4L2_XFER_FUNC_709``. The default Y'CbCr encoding is
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``V4L2_YCBCR_ENC_601``. The default Y'CbCr quantization is limited
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range. The chromaticities of the primary colors and the white reference
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are:
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.. tabularcolumns:: |p{4.4cm}|p{4.4cm}|p{8.7cm}|
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.. flat-table:: SMPTE 170M Chromaticities
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:header-rows: 1
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:stub-columns: 0
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:widths: 1 1 2
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- .. row 1
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- Color
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- x
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- y
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- .. row 2
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- Red
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- 0.630
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- 0.340
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- .. row 3
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- Green
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- 0.310
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- 0.595
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- .. row 4
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- Blue
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- 0.155
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- 0.070
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- .. row 5
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- White Reference (D65)
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- 0.3127
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- 0.3290
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The red, green and blue chromaticities are also often referred to as the
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SMPTE C set, so this colorspace is sometimes called SMPTE C as well.
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The transfer function defined for SMPTE 170M is the same as the one
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defined in Rec. 709.
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.. math::
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L' = -1.099(-L)^{0.45} + 0.099 \text{, for } L \le-0.018
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L' = 4.5L \text{, for } -0.018 < L < 0.018
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L' = 1.099L^{0.45} - 0.099 \text{, for } L \ge 0.018
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Inverse Transfer function:
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.. math::
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L = -\left( \frac{L' - 0.099}{-1.099} \right) ^{\frac{1}{0.45}} \text{, for } L' \le -0.081
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L = \frac{L'}{4.5} \text{, for } -0.081 < L' < 0.081
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L = \left(\frac{L' + 0.099}{1.099}\right)^{\frac{1}{0.45} } \text{, for } L' \ge 0.081
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The luminance (Y') and color difference (Cb and Cr) are obtained with
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the following ``V4L2_YCBCR_ENC_601`` encoding:
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.. math::
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Y' = 0.299R' + 0.587G' + 0.114B'
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Cb = -0.169R' - 0.331G' + 0.5B'
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Cr = 0.5R' - 0.419G' - 0.081B'
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Y' is clamped to the range [0…1] and Cb and Cr are clamped to the range
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[-0.5…0.5]. This conversion to Y'CbCr is identical to the one defined in
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the :ref:`itu601` standard and this colorspace is sometimes called
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BT.601 as well, even though BT.601 does not mention any color primaries.
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The default quantization is limited range, but full range is possible
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although rarely seen.
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.. _col-rec709:
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Colorspace Rec. 709 (V4L2_COLORSPACE_REC709)
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============================================
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The :ref:`itu709` standard defines the colorspace used by HDTV in
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general. The default transfer function is ``V4L2_XFER_FUNC_709``. The
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default Y'CbCr encoding is ``V4L2_YCBCR_ENC_709``. The default Y'CbCr
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quantization is limited range. The chromaticities of the primary colors
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and the white reference are:
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.. tabularcolumns:: |p{4.4cm}|p{4.4cm}|p{8.7cm}|
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.. flat-table:: Rec. 709 Chromaticities
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:header-rows: 1
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:stub-columns: 0
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:widths: 1 1 2
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- .. row 1
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- Color
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- x
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- y
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- .. row 2
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- Red
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- 0.640
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- 0.330
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- .. row 3
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- Green
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- 0.300
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- 0.600
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- .. row 4
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- Blue
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- 0.150
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- 0.060
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- .. row 5
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- White Reference (D65)
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- 0.3127
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- 0.3290
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The full name of this standard is Rec. ITU-R BT.709-5.
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Transfer function. Normally L is in the range [0…1], but for the
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extended gamut xvYCC encoding values outside that range are allowed.
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.. math::
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L' = -1.099(-L)^{0.45} + 0.099 \text{, for } L \le -0.018
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L' = 4.5L \text{, for } -0.018 < L < 0.018
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L' = 1.099L^{0.45} - 0.099 \text{, for } L \ge 0.018
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Inverse Transfer function:
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.. math::
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L = -\left( \frac{L' - 0.099}{-1.099} \right)^\frac{1}{0.45} \text{, for } L' \le -0.081
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L = \frac{L'}{4.5}\text{, for } -0.081 < L' < 0.081
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L = \left(\frac{L' + 0.099}{1.099}\right)^{\frac{1}{0.45} } \text{, for } L' \ge 0.081
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The luminance (Y') and color difference (Cb and Cr) are obtained with
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the following ``V4L2_YCBCR_ENC_709`` encoding:
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.. math::
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Y' = 0.2126R' + 0.7152G' + 0.0722B'
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Cb = -0.1146R' - 0.3854G' + 0.5B'
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Cr = 0.5R' - 0.4542G' - 0.0458B'
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Y' is clamped to the range [0…1] and Cb and Cr are clamped to the range
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[-0.5…0.5].
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The default quantization is limited range, but full range is possible
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although rarely seen.
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The ``V4L2_YCBCR_ENC_709`` encoding described above is the default for
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this colorspace, but it can be overridden with ``V4L2_YCBCR_ENC_601``,
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in which case the BT.601 Y'CbCr encoding is used.
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Two additional extended gamut Y'CbCr encodings are also possible with
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this colorspace:
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The xvYCC 709 encoding (``V4L2_YCBCR_ENC_XV709``, :ref:`xvycc`) is
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similar to the Rec. 709 encoding, but it allows for R', G' and B' values
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that are outside the range [0…1]. The resulting Y', Cb and Cr values are
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scaled and offset:
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.. math::
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Y' = \frac{219}{256} * (0.2126R' + 0.7152G' + 0.0722B') + \frac{16}{256}
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Cb = \frac{224}{256} * (-0.1146R' - 0.3854G' + 0.5B')
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Cr = \frac{224}{256} * (0.5R' - 0.4542G' - 0.0458B')
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The xvYCC 601 encoding (``V4L2_YCBCR_ENC_XV601``, :ref:`xvycc`) is
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similar to the BT.601 encoding, but it allows for R', G' and B' values
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that are outside the range [0…1]. The resulting Y', Cb and Cr values are
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scaled and offset:
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.. math::
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Y' = \frac{219}{256} * (0.299R' + 0.587G' + 0.114B') + \frac{16}{256}
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Cb = \frac{224}{256} * (-0.169R' - 0.331G' + 0.5B')
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Cr = \frac{224}{256} * (0.5R' - 0.419G' - 0.081B')
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Y' is clamped to the range [0…1] and Cb and Cr are clamped to the range
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[-0.5…0.5]. The non-standard xvYCC 709 or xvYCC 601 encodings can be
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used by selecting ``V4L2_YCBCR_ENC_XV709`` or ``V4L2_YCBCR_ENC_XV601``.
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The xvYCC encodings always use full range quantization.
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.. _col-srgb:
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Colorspace sRGB (V4L2_COLORSPACE_SRGB)
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======================================
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The :ref:`srgb` standard defines the colorspace used by most webcams
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and computer graphics. The default transfer function is
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``V4L2_XFER_FUNC_SRGB``. The default Y'CbCr encoding is
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``V4L2_YCBCR_ENC_SYCC``. The default Y'CbCr quantization is full range.
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The chromaticities of the primary colors and the white reference are:
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.. tabularcolumns:: |p{4.4cm}|p{4.4cm}|p{8.7cm}|
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.. flat-table:: sRGB Chromaticities
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:header-rows: 1
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:stub-columns: 0
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:widths: 1 1 2
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- .. row 1
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- Color
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- x
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- y
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- .. row 2
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- Red
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- 0.640
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- 0.330
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- .. row 3
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- Green
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- 0.300
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- 0.600
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- .. row 4
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- Blue
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- 0.150
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- 0.060
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- .. row 5
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- White Reference (D65)
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- 0.3127
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- 0.3290
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These chromaticities are identical to the Rec. 709 colorspace.
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Transfer function. Note that negative values for L are only used by the
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Y'CbCr conversion.
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.. math::
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L' = -1.055(-L)^{\frac{1}{2.4} } + 0.055\text{, for }L < -0.0031308
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L' = 12.92L\text{, for }-0.0031308 \le L \le 0.0031308
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L' = 1.055L ^{\frac{1}{2.4} } - 0.055\text{, for }0.0031308 < L \le 1
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Inverse Transfer function:
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.. math::
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L = -((-L' + 0.055) / 1.055) ^{2.4}\text{, for }L' < -0.04045
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L = L' / 12.92\text{, for }-0.04045 \le L' \le 0.04045
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L = ((L' + 0.055) / 1.055) ^{2.4}\text{, for }L' > 0.04045
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The luminance (Y') and color difference (Cb and Cr) are obtained with
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the following ``V4L2_YCBCR_ENC_SYCC`` encoding as defined by
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:ref:`sycc`:
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.. math::
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Y' = 0.2990R' + 0.5870G' + 0.1140B'
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Cb = -0.1687R' - 0.3313G' + 0.5B'
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Cr = 0.5R' - 0.4187G' - 0.0813B'
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Y' is clamped to the range [0…1] and Cb and Cr are clamped to the range
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[-0.5…0.5]. The ``V4L2_YCBCR_ENC_SYCC`` quantization is always full
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range. Although this Y'CbCr encoding looks very similar to the
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``V4L2_YCBCR_ENC_XV601`` encoding, it is not. The
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``V4L2_YCBCR_ENC_XV601`` scales and offsets the Y'CbCr values before
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quantization, but this encoding does not do that.
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.. _col-adobergb:
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Colorspace Adobe RGB (V4L2_COLORSPACE_ADOBERGB)
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===============================================
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The :ref:`adobergb` standard defines the colorspace used by computer
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graphics that use the AdobeRGB colorspace. This is also known as the
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:ref:`oprgb` standard. The default transfer function is
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``V4L2_XFER_FUNC_ADOBERGB``. The default Y'CbCr encoding is
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``V4L2_YCBCR_ENC_601``. The default Y'CbCr quantization is limited
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range. The chromaticities of the primary colors and the white reference
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are:
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.. tabularcolumns:: |p{4.4cm}|p{4.4cm}|p{8.7cm}|
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.. flat-table:: Adobe RGB Chromaticities
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:header-rows: 1
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:stub-columns: 0
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:widths: 1 1 2
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- .. row 1
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- Color
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- x
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- y
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- .. row 2
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- Red
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- 0.6400
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- 0.3300
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- .. row 3
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- Green
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- 0.2100
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- 0.7100
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- .. row 4
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- Blue
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- 0.1500
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- 0.0600
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- .. row 5
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- White Reference (D65)
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- 0.3127
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- 0.3290
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Transfer function:
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.. math::
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L' = L ^{\frac{1}{2.19921875}}
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Inverse Transfer function:
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.. math::
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L = L'^{(2.19921875)}
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The luminance (Y') and color difference (Cb and Cr) are obtained with
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the following ``V4L2_YCBCR_ENC_601`` encoding:
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.. math::
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Y' = 0.299R' + 0.587G' + 0.114B'
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Cb = -0.169R' - 0.331G' + 0.5B'
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Cr = 0.5R' - 0.419G' - 0.081B'
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Y' is clamped to the range [0…1] and Cb and Cr are clamped to the range
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[-0.5…0.5]. This transform is identical to one defined in SMPTE
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170M/BT.601. The Y'CbCr quantization is limited range.
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.. _col-bt2020:
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Colorspace BT.2020 (V4L2_COLORSPACE_BT2020)
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===========================================
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The :ref:`itu2020` standard defines the colorspace used by Ultra-high
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definition television (UHDTV). The default transfer function is
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``V4L2_XFER_FUNC_709``. The default Y'CbCr encoding is
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``V4L2_YCBCR_ENC_BT2020``. The default R'G'B' quantization is limited
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range (!), and so is the default Y'CbCr quantization. The chromaticities
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of the primary colors and the white reference are:
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.. tabularcolumns:: |p{4.4cm}|p{4.4cm}|p{8.7cm}|
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.. flat-table:: BT.2020 Chromaticities
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:header-rows: 1
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:stub-columns: 0
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:widths: 1 1 2
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- .. row 1
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- Color
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- x
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- y
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- .. row 2
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- Red
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- 0.708
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- 0.292
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- .. row 3
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- Green
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- 0.170
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- 0.797
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- .. row 4
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- Blue
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- 0.131
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- 0.046
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- .. row 5
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- White Reference (D65)
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- 0.3127
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- 0.3290
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Transfer function (same as Rec. 709):
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.. math::
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L' = 4.5L\text{, for }0 \le L < 0.018
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L' = 1.099L ^{0.45} - 0.099\text{, for } 0.018 \le L \le 1
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Inverse Transfer function:
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.. math::
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L = L' / 4.5\text{, for } L' < 0.081
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L = \left( \frac{L' + 0.099}{1.099}\right) ^{\frac{1}{0.45} }\text{, for } L' \ge 0.081
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The luminance (Y') and color difference (Cb and Cr) are obtained with
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the following ``V4L2_YCBCR_ENC_BT2020`` encoding:
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.. math::
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Y' = 0.2627R' + 0.6780G' + 0.0593B'
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Cb = -0.1396R' - 0.3604G' + 0.5B'
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Cr = 0.5R' - 0.4598G' - 0.0402B'
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Y' is clamped to the range [0…1] and Cb and Cr are clamped to the range
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[-0.5…0.5]. The Y'CbCr quantization is limited range.
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There is also an alternate constant luminance R'G'B' to Yc'CbcCrc
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(``V4L2_YCBCR_ENC_BT2020_CONST_LUM``) encoding:
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Luma:
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.. math::
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:nowrap:
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\begin{align*}
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Yc' = (0.2627R + 0.6780G + 0.0593B)'& \\
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B' - Yc' \le 0:& \\
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&Cbc = (B' - Yc') / 1.9404 \\
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B' - Yc' > 0: & \\
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&Cbc = (B' - Yc') / 1.5816 \\
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R' - Yc' \le 0:& \\
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&Crc = (R' - Y') / 1.7184 \\
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R' - Yc' > 0:& \\
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&Crc = (R' - Y') / 0.9936
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\end{align*}
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Yc' is clamped to the range [0…1] and Cbc and Crc are clamped to the
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range [-0.5…0.5]. The Yc'CbcCrc quantization is limited range.
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.. _col-dcip3:
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Colorspace DCI-P3 (V4L2_COLORSPACE_DCI_P3)
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==========================================
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The :ref:`smpte431` standard defines the colorspace used by cinema
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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``.
|
|
|
|
.. note::
|
|
|
|
Note that this colorspace 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
|
|
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:: DCI-P3 Chromaticities
|
|
:header-rows: 1
|
|
:stub-columns: 0
|
|
:widths: 1 1 2
|
|
|
|
|
|
- .. row 1
|
|
|
|
- Color
|
|
|
|
- x
|
|
|
|
- y
|
|
|
|
- .. row 2
|
|
|
|
- Red
|
|
|
|
- 0.6800
|
|
|
|
- 0.3200
|
|
|
|
- .. row 3
|
|
|
|
- Green
|
|
|
|
- 0.2650
|
|
|
|
- 0.6900
|
|
|
|
- .. row 4
|
|
|
|
- Blue
|
|
|
|
- 0.1500
|
|
|
|
- 0.0600
|
|
|
|
- .. row 5
|
|
|
|
- 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
|
|
|
|
|
|
- .. row 1
|
|
|
|
- Color
|
|
|
|
- x
|
|
|
|
- y
|
|
|
|
- .. row 2
|
|
|
|
- Red
|
|
|
|
- 0.630
|
|
|
|
- 0.340
|
|
|
|
- .. row 3
|
|
|
|
- Green
|
|
|
|
- 0.310
|
|
|
|
- 0.595
|
|
|
|
- .. row 4
|
|
|
|
- Blue
|
|
|
|
- 0.155
|
|
|
|
- 0.070
|
|
|
|
- .. row 5
|
|
|
|
- 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'
|
|
|
|
Yc' is clamped to the range [0…1] and Cbc and Crc 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
|
|
|
|
|
|
- .. row 1
|
|
|
|
- Color
|
|
|
|
- x
|
|
|
|
- y
|
|
|
|
- .. row 2
|
|
|
|
- Red
|
|
|
|
- 0.67
|
|
|
|
- 0.33
|
|
|
|
- .. row 3
|
|
|
|
- Green
|
|
|
|
- 0.21
|
|
|
|
- 0.71
|
|
|
|
- .. row 4
|
|
|
|
- Blue
|
|
|
|
- 0.14
|
|
|
|
- 0.08
|
|
|
|
- .. row 5
|
|
|
|
- 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' = 0.299R' + 0.587G' + 0.114B'
|
|
|
|
Cb = -0.169R' - 0.331G' + 0.5B'
|
|
|
|
Cr = 0.5R' - 0.419G' - 0.081B'
|
|
|
|
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
|
|
|
|
|
|
- .. row 1
|
|
|
|
- Color
|
|
|
|
- x
|
|
|
|
- y
|
|
|
|
- .. row 2
|
|
|
|
- Red
|
|
|
|
- 0.64
|
|
|
|
- 0.33
|
|
|
|
- .. row 3
|
|
|
|
- Green
|
|
|
|
- 0.29
|
|
|
|
- 0.60
|
|
|
|
- .. row 4
|
|
|
|
- Blue
|
|
|
|
- 0.15
|
|
|
|
- 0.06
|
|
|
|
- .. row 5
|
|
|
|
- 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' = 0.299R' + 0.587G' + 0.114B'
|
|
|
|
Cb = -0.169R' - 0.331G' + 0.5B'
|
|
|
|
Cr = 0.5R' - 0.419G' - 0.081B'
|
|
|
|
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``.
|