150 lines
4.9 KiB
ReStructuredText
150 lines
4.9 KiB
ReStructuredText
.. -*- coding: utf-8; mode: rst -*-
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****************************
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Defining Colorspaces in V4L2
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****************************
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In V4L2 colorspaces are defined by four values. The first is the
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colorspace identifier (enum :c:type:`v4l2_colorspace`)
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which defines the chromaticities, the default transfer function, the
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default Y'CbCr encoding and the default quantization method. The second
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is the transfer function identifier (enum
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:c:type:`v4l2_xfer_func`) to specify non-standard
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transfer functions. The third is the Y'CbCr encoding identifier (enum
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:c:type:`v4l2_ycbcr_encoding`) to specify
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non-standard Y'CbCr encodings and the fourth is the quantization
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identifier (enum :c:type:`v4l2_quantization`) to
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specify non-standard quantization methods. Most of the time only the
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colorspace field of struct :c:type:`v4l2_pix_format`
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or struct :c:type:`v4l2_pix_format_mplane`
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needs to be filled in.
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.. note::
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The default R'G'B' quantization is full range for all
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colorspaces except for BT.2020 which uses limited range R'G'B'
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quantization.
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.. tabularcolumns:: |p{6.0cm}|p{11.5cm}|
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.. c:type:: v4l2_colorspace
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.. flat-table:: V4L2 Colorspaces
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:header-rows: 1
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:stub-columns: 0
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* - Identifier
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- Details
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* - ``V4L2_COLORSPACE_DEFAULT``
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- The default colorspace. This can be used by applications to let
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the driver fill in the colorspace.
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* - ``V4L2_COLORSPACE_SMPTE170M``
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- See :ref:`col-smpte-170m`.
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* - ``V4L2_COLORSPACE_REC709``
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- See :ref:`col-rec709`.
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* - ``V4L2_COLORSPACE_SRGB``
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- See :ref:`col-srgb`.
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* - ``V4L2_COLORSPACE_ADOBERGB``
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- See :ref:`col-adobergb`.
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* - ``V4L2_COLORSPACE_BT2020``
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- See :ref:`col-bt2020`.
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* - ``V4L2_COLORSPACE_DCI_P3``
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- See :ref:`col-dcip3`.
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* - ``V4L2_COLORSPACE_SMPTE240M``
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- See :ref:`col-smpte-240m`.
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* - ``V4L2_COLORSPACE_470_SYSTEM_M``
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- See :ref:`col-sysm`.
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* - ``V4L2_COLORSPACE_470_SYSTEM_BG``
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- See :ref:`col-sysbg`.
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* - ``V4L2_COLORSPACE_JPEG``
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- See :ref:`col-jpeg`.
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* - ``V4L2_COLORSPACE_RAW``
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- The raw colorspace. This is used for raw image capture where the
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image is minimally processed and is using the internal colorspace
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of the device. The software that processes an image using this
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'colorspace' will have to know the internals of the capture
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device.
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.. c:type:: v4l2_xfer_func
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.. flat-table:: V4L2 Transfer Function
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:header-rows: 1
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:stub-columns: 0
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* - Identifier
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- Details
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* - ``V4L2_XFER_FUNC_DEFAULT``
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- Use the default transfer function as defined by the colorspace.
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* - ``V4L2_XFER_FUNC_709``
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- Use the Rec. 709 transfer function.
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* - ``V4L2_XFER_FUNC_SRGB``
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- Use the sRGB transfer function.
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* - ``V4L2_XFER_FUNC_ADOBERGB``
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- Use the AdobeRGB transfer function.
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* - ``V4L2_XFER_FUNC_SMPTE240M``
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- Use the SMPTE 240M transfer function.
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* - ``V4L2_XFER_FUNC_NONE``
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- Do not use a transfer function (i.e. use linear RGB values).
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* - ``V4L2_XFER_FUNC_DCI_P3``
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- Use the DCI-P3 transfer function.
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* - ``V4L2_XFER_FUNC_SMPTE2084``
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- Use the SMPTE 2084 transfer function.
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.. c:type:: v4l2_ycbcr_encoding
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.. tabularcolumns:: |p{6.5cm}|p{11.0cm}|
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.. flat-table:: V4L2 Y'CbCr Encodings
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:header-rows: 1
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:stub-columns: 0
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* - Identifier
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- Details
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* - ``V4L2_YCBCR_ENC_DEFAULT``
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- Use the default Y'CbCr encoding as defined by the colorspace.
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* - ``V4L2_YCBCR_ENC_601``
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- Use the BT.601 Y'CbCr encoding.
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* - ``V4L2_YCBCR_ENC_709``
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- Use the Rec. 709 Y'CbCr encoding.
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* - ``V4L2_YCBCR_ENC_XV601``
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- Use the extended gamut xvYCC BT.601 encoding.
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* - ``V4L2_YCBCR_ENC_XV709``
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- Use the extended gamut xvYCC Rec. 709 encoding.
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* - ``V4L2_YCBCR_ENC_BT2020``
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- Use the default non-constant luminance BT.2020 Y'CbCr encoding.
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* - ``V4L2_YCBCR_ENC_BT2020_CONST_LUM``
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- Use the constant luminance BT.2020 Yc'CbcCrc encoding.
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* - ``V4L2_YCBCR_ENC_SMPTE_240M``
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- Use the SMPTE 240M Y'CbCr encoding.
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.. c:type:: v4l2_quantization
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.. tabularcolumns:: |p{6.5cm}|p{11.0cm}|
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.. flat-table:: V4L2 Quantization Methods
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:header-rows: 1
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:stub-columns: 0
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* - Identifier
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- Details
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* - ``V4L2_QUANTIZATION_DEFAULT``
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- Use the default quantization encoding as defined by the
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colorspace. This is always full range for R'G'B' (except for the
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BT.2020 colorspace) and usually limited range for Y'CbCr.
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* - ``V4L2_QUANTIZATION_FULL_RANGE``
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- Use the full range quantization encoding. I.e. the range [0…1] is
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mapped to [0…255] (with possible clipping to [1…254] to avoid the
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0x00 and 0xff values). Cb and Cr are mapped from [-0.5…0.5] to
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[0…255] (with possible clipping to [1…254] to avoid the 0x00 and
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0xff values).
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* - ``V4L2_QUANTIZATION_LIM_RANGE``
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- Use the limited range quantization encoding. I.e. the range [0…1]
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is mapped to [16…235]. Cb and Cr are mapped from [-0.5…0.5] to
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[16…240].
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