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diff --git a/Documentation/userspace-api/media/v4l/colorspaces-defs.rst b/Documentation/userspace-api/media/v4l/colorspaces-defs.rst new file mode 100644 index 000000000000..01404e1f609a --- /dev/null +++ b/Documentation/userspace-api/media/v4l/colorspaces-defs.rst @@ -0,0 +1,183 @@ +.. Permission is granted to copy, distribute and/or modify this +.. document under the terms of the GNU Free Documentation License, +.. Version 1.1 or any later version published by the Free Software +.. Foundation, with no Invariant Sections, no Front-Cover Texts +.. and no Back-Cover Texts. A copy of the license is included at +.. Documentation/userspace-api/media/fdl-appendix.rst. +.. +.. TODO: replace it to GFDL-1.1-or-later WITH no-invariant-sections + +**************************** +Defining Colorspaces in V4L2 +**************************** + +In V4L2 colorspaces are defined by four values. The first is the +colorspace identifier (enum :c:type:`v4l2_colorspace`) +which defines the chromaticities, the default transfer function, the +default Y'CbCr encoding and the default quantization method. The second +is the transfer function identifier (enum +:c:type:`v4l2_xfer_func`) to specify non-standard +transfer functions. The third is the Y'CbCr encoding identifier (enum +:c:type:`v4l2_ycbcr_encoding`) to specify +non-standard Y'CbCr encodings and the fourth is the quantization +identifier (enum :c:type:`v4l2_quantization`) to +specify non-standard quantization methods. Most of the time only the +colorspace field of struct :c:type:`v4l2_pix_format` +or struct :c:type:`v4l2_pix_format_mplane` +needs to be filled in. + +.. _hsv-colorspace: + +On :ref:`HSV formats <hsv-formats>` the *Hue* is defined as the angle on +the cylindrical color representation. Usually this angle is measured in +degrees, i.e. 0-360. When we map this angle value into 8 bits, there are +two basic ways to do it: Divide the angular value by 2 (0-179), or use the +whole range, 0-255, dividing the angular value by 1.41. The enum +:c:type:`v4l2_hsv_encoding` specifies which encoding is used. + +.. note:: The default R'G'B' quantization is full range for all + colorspaces except for BT.2020 which uses limited range R'G'B' + quantization. + +.. tabularcolumns:: |p{6.7cm}|p{10.8cm}| + +.. c:type:: v4l2_colorspace + +.. flat-table:: V4L2 Colorspaces + :header-rows: 1 + :stub-columns: 0 + + * - Identifier + - Details + * - ``V4L2_COLORSPACE_DEFAULT`` + - The default colorspace. This can be used by applications to let + the driver fill in the colorspace. + * - ``V4L2_COLORSPACE_SMPTE170M`` + - See :ref:`col-smpte-170m`. + * - ``V4L2_COLORSPACE_REC709`` + - See :ref:`col-rec709`. + * - ``V4L2_COLORSPACE_SRGB`` + - See :ref:`col-srgb`. + * - ``V4L2_COLORSPACE_OPRGB`` + - See :ref:`col-oprgb`. + * - ``V4L2_COLORSPACE_BT2020`` + - See :ref:`col-bt2020`. + * - ``V4L2_COLORSPACE_DCI_P3`` + - See :ref:`col-dcip3`. + * - ``V4L2_COLORSPACE_SMPTE240M`` + - See :ref:`col-smpte-240m`. + * - ``V4L2_COLORSPACE_470_SYSTEM_M`` + - See :ref:`col-sysm`. + * - ``V4L2_COLORSPACE_470_SYSTEM_BG`` + - See :ref:`col-sysbg`. + * - ``V4L2_COLORSPACE_JPEG`` + - See :ref:`col-jpeg`. + * - ``V4L2_COLORSPACE_RAW`` + - The raw colorspace. This is used for raw image capture where the + image is minimally processed and is using the internal colorspace + of the device. The software that processes an image using this + 'colorspace' will have to know the internals of the capture + device. + + + +.. c:type:: v4l2_xfer_func + +.. tabularcolumns:: |p{5.5cm}|p{12.0cm}| + +.. flat-table:: V4L2 Transfer Function + :header-rows: 1 + :stub-columns: 0 + + * - Identifier + - Details + * - ``V4L2_XFER_FUNC_DEFAULT`` + - Use the default transfer function as defined by the colorspace. + * - ``V4L2_XFER_FUNC_709`` + - Use the Rec. 709 transfer function. + * - ``V4L2_XFER_FUNC_SRGB`` + - Use the sRGB transfer function. + * - ``V4L2_XFER_FUNC_OPRGB`` + - Use the opRGB transfer function. + * - ``V4L2_XFER_FUNC_SMPTE240M`` + - Use the SMPTE 240M transfer function. + * - ``V4L2_XFER_FUNC_NONE`` + - Do not use a transfer function (i.e. use linear RGB values). + * - ``V4L2_XFER_FUNC_DCI_P3`` + - Use the DCI-P3 transfer function. + * - ``V4L2_XFER_FUNC_SMPTE2084`` + - Use the SMPTE 2084 transfer function. See :ref:`xf-smpte-2084`. + + + +.. c:type:: v4l2_ycbcr_encoding + +.. tabularcolumns:: |p{7.2cm}|p{10.3cm}| + +.. flat-table:: V4L2 Y'CbCr Encodings + :header-rows: 1 + :stub-columns: 0 + + * - Identifier + - Details + * - ``V4L2_YCBCR_ENC_DEFAULT`` + - Use the default Y'CbCr encoding as defined by the colorspace. + * - ``V4L2_YCBCR_ENC_601`` + - Use the BT.601 Y'CbCr encoding. + * - ``V4L2_YCBCR_ENC_709`` + - Use the Rec. 709 Y'CbCr encoding. + * - ``V4L2_YCBCR_ENC_XV601`` + - Use the extended gamut xvYCC BT.601 encoding. + * - ``V4L2_YCBCR_ENC_XV709`` + - Use the extended gamut xvYCC Rec. 709 encoding. + * - ``V4L2_YCBCR_ENC_BT2020`` + - Use the default non-constant luminance BT.2020 Y'CbCr encoding. + * - ``V4L2_YCBCR_ENC_BT2020_CONST_LUM`` + - Use the constant luminance BT.2020 Yc'CbcCrc encoding. + * - ``V4L2_YCBCR_ENC_SMPTE_240M`` + - Use the SMPTE 240M Y'CbCr encoding. + + + +.. c:type:: v4l2_hsv_encoding + +.. tabularcolumns:: |p{6.5cm}|p{11.0cm}| + +.. flat-table:: V4L2 HSV Encodings + :header-rows: 1 + :stub-columns: 0 + + * - Identifier + - Details + * - ``V4L2_HSV_ENC_180`` + - For the Hue, each LSB is two degrees. + * - ``V4L2_HSV_ENC_256`` + - For the Hue, the 360 degrees are mapped into 8 bits, i.e. each + LSB is roughly 1.41 degrees. + + + +.. c:type:: v4l2_quantization + +.. tabularcolumns:: |p{6.5cm}|p{11.0cm}| + +.. flat-table:: V4L2 Quantization Methods + :header-rows: 1 + :stub-columns: 0 + + * - Identifier + - Details + * - ``V4L2_QUANTIZATION_DEFAULT`` + - Use the default quantization encoding as defined by the + colorspace. This is always full range for R'G'B' (except for the + BT.2020 colorspace) and HSV. It is usually limited range for Y'CbCr. + * - ``V4L2_QUANTIZATION_FULL_RANGE`` + - Use the full range quantization encoding. I.e. the range [0…1] is + mapped to [0…255] (with possible clipping to [1…254] to avoid the + 0x00 and 0xff values). Cb and Cr are mapped from [-0.5…0.5] to + [0…255] (with possible clipping to [1…254] to avoid the 0x00 and + 0xff values). + * - ``V4L2_QUANTIZATION_LIM_RANGE`` + - Use the limited range quantization encoding. I.e. the range [0…1] + is mapped to [16…235]. Cb and Cr are mapped from [-0.5…0.5] to + [16…240]. |