79e92dc0ec
The xvYCC601/709 encodings were mapped by default to full range quantization. This is actually wrong since these encodings use limited range quantization, but accept values outside of the limited range. This makes sense since for values within the limited range it behaves exactly the same as BT.601 or Rec. 709. The only difference is that with the xvYCC encodings the values outside of the limited range also produce value colors. Talking to people who know a lot more about this than I do made me realize that mapping xvYCC to full range quantization was wrong, so this patch corrects this and also improves the documentation. These formats are very rare, and since the formula for decoding these Y'CbCr encodings is actually fixed and independent of the quantization field value it is safe to make this change. The main advantage is that keeps the V4L2 specification in sync with the corresponding colorspace, HDMI and CEA861 standards when it comes to these xvYCC formats. Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com> Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>
761 lines
19 KiB
ReStructuredText
761 lines
19 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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* - Color
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- x
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- y
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* - Red
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- 0.630
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- 0.340
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* - Green
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- 0.310
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- 0.595
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* - Blue
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- 0.155
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- 0.070
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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' = 0.2990R' + 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]. 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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* - Color
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- x
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- y
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* - Red
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- 0.640
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- 0.330
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* - Green
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- 0.300
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- 0.600
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* - Blue
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- 0.150
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- 0.060
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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 according to the limited range formula:
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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 according to the limited range formula:
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.. math::
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Y' = \frac{219}{256} * (0.2990R' + 0.5870G' + 0.1140B') + \frac{16}{256}
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Cb = \frac{224}{256} * (-0.1687R' - 0.3313G' + 0.5B')
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Cr = \frac{224}{256} * (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] and quantized without further scaling or offsets.
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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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As seen by the xvYCC formulas these encodings always use limited range quantization,
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there is no full range variant. The whole point of these extended gamut encodings
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is that values outside the limited range are still valid, although they
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map to R', G' and B' values outside the [0…1] range and are therefore outside
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the Rec. 709 colorspace gamut.
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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_601``. The default Y'CbCr quantization is limited range.
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Note that the :ref:`sycc` standard specifies full range quantization,
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however all current capture hardware supported by the kernel convert
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R'G'B' to limited range Y'CbCr. So choosing full range as the default
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would break how applications interpret the quantization 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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* - Color
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- x
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- y
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* - Red
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- 0.640
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- 0.330
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* - Green
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- 0.300
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- 0.600
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* - Blue
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- 0.150
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- 0.060
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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_601`` encoding as defined by :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]. 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-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.
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Note that the :ref:`oprgb` standard specifies full range quantization,
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however all current capture hardware supported by the kernel convert
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R'G'B' to limited range Y'CbCr. So choosing full range as the default
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would break how applications interpret the quantization 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:: 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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* - Color
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- x
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- y
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* - Red
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- 0.6400
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- 0.3300
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* - Green
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- 0.2100
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- 0.7100
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* - Blue
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- 0.1500
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- 0.0600
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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' = 0.2990R' + 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]. 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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* - Color
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- x
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- y
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* - Red
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- 0.708
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- 0.292
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* - Green
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- 0.170
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- 0.797
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* - Blue
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- 0.131
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- 0.046
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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
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is ``V4L2_XFER_FUNC_DCI_P3``. The default Y'CbCr encoding is
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``V4L2_YCBCR_ENC_709``. The default Y'CbCr quantization is limited range.
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.. note::
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Note that this colorspace standard does not specify a
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Y'CbCr encoding since it is not meant to be encoded to Y'CbCr. So this
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default Y'CbCr encoding was picked because it is the HDTV encoding.
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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:: DCI-P3 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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* - Color
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- x
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- y
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* - 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``.
|