1.. -*- coding: utf-8; mode: rst -*- 2 3**************************** 4Defining Colorspaces in V4L2 5**************************** 6 7In V4L2 colorspaces are defined by four values. The first is the 8colorspace identifier (enum :c:type:`v4l2_colorspace`) 9which defines the chromaticities, the default transfer function, the 10default Y'CbCr encoding and the default quantization method. The second 11is the transfer function identifier (enum 12:c:type:`v4l2_xfer_func`) to specify non-standard 13transfer functions. The third is the Y'CbCr encoding identifier (enum 14:c:type:`v4l2_ycbcr_encoding`) to specify 15non-standard Y'CbCr encodings and the fourth is the quantization 16identifier (enum :c:type:`v4l2_quantization`) to 17specify non-standard quantization methods. Most of the time only the 18colorspace field of struct :c:type:`v4l2_pix_format` 19or struct :c:type:`v4l2_pix_format_mplane` 20needs to be filled in. 21 22.. _hsv-colorspace: 23 24On :ref:`HSV formats <hsv-formats>` the *Hue* is defined as the angle on 25the cylindrical color representation. Usually this angle is measured in 26degrees, i.e. 0-360. When we map this angle value into 8 bits, there are 27two basic ways to do it: Divide the angular value by 2 (0-179), or use the 28whole range, 0-255, dividing the angular value by 1.41. The enum 29:c:type:`v4l2_hsv_encoding` specifies which encoding is used. 30 31.. note:: The default R'G'B' quantization is full range for all 32 colorspaces except for BT.2020 which uses limited range R'G'B' 33 quantization. 34 35.. tabularcolumns:: |p{6.0cm}|p{11.5cm}| 36 37.. c:type:: v4l2_colorspace 38 39.. flat-table:: V4L2 Colorspaces 40 :header-rows: 1 41 :stub-columns: 0 42 43 * - Identifier 44 - Details 45 * - ``V4L2_COLORSPACE_DEFAULT`` 46 - The default colorspace. This can be used by applications to let 47 the driver fill in the colorspace. 48 * - ``V4L2_COLORSPACE_SMPTE170M`` 49 - See :ref:`col-smpte-170m`. 50 * - ``V4L2_COLORSPACE_REC709`` 51 - See :ref:`col-rec709`. 52 * - ``V4L2_COLORSPACE_SRGB`` 53 - See :ref:`col-srgb`. 54 * - ``V4L2_COLORSPACE_OPRGB`` 55 - See :ref:`col-oprgb`. 56 * - ``V4L2_COLORSPACE_BT2020`` 57 - See :ref:`col-bt2020`. 58 * - ``V4L2_COLORSPACE_DCI_P3`` 59 - See :ref:`col-dcip3`. 60 * - ``V4L2_COLORSPACE_SMPTE240M`` 61 - See :ref:`col-smpte-240m`. 62 * - ``V4L2_COLORSPACE_470_SYSTEM_M`` 63 - See :ref:`col-sysm`. 64 * - ``V4L2_COLORSPACE_470_SYSTEM_BG`` 65 - See :ref:`col-sysbg`. 66 * - ``V4L2_COLORSPACE_JPEG`` 67 - See :ref:`col-jpeg`. 68 * - ``V4L2_COLORSPACE_RAW`` 69 - The raw colorspace. This is used for raw image capture where the 70 image is minimally processed and is using the internal colorspace 71 of the device. The software that processes an image using this 72 'colorspace' will have to know the internals of the capture 73 device. 74 75 76 77.. c:type:: v4l2_xfer_func 78 79.. tabularcolumns:: |p{5.5cm}|p{12.0cm}| 80 81.. flat-table:: V4L2 Transfer Function 82 :header-rows: 1 83 :stub-columns: 0 84 85 * - Identifier 86 - Details 87 * - ``V4L2_XFER_FUNC_DEFAULT`` 88 - Use the default transfer function as defined by the colorspace. 89 * - ``V4L2_XFER_FUNC_709`` 90 - Use the Rec. 709 transfer function. 91 * - ``V4L2_XFER_FUNC_SRGB`` 92 - Use the sRGB transfer function. 93 * - ``V4L2_XFER_FUNC_OPRGB`` 94 - Use the opRGB transfer function. 95 * - ``V4L2_XFER_FUNC_SMPTE240M`` 96 - Use the SMPTE 240M transfer function. 97 * - ``V4L2_XFER_FUNC_NONE`` 98 - Do not use a transfer function (i.e. use linear RGB values). 99 * - ``V4L2_XFER_FUNC_DCI_P3`` 100 - Use the DCI-P3 transfer function. 101 * - ``V4L2_XFER_FUNC_SMPTE2084`` 102 - Use the SMPTE 2084 transfer function. See :ref:`xf-smpte-2084`. 103 104 105 106.. c:type:: v4l2_ycbcr_encoding 107 108.. tabularcolumns:: |p{6.5cm}|p{11.0cm}| 109 110.. flat-table:: V4L2 Y'CbCr Encodings 111 :header-rows: 1 112 :stub-columns: 0 113 114 * - Identifier 115 - Details 116 * - ``V4L2_YCBCR_ENC_DEFAULT`` 117 - Use the default Y'CbCr encoding as defined by the colorspace. 118 * - ``V4L2_YCBCR_ENC_601`` 119 - Use the BT.601 Y'CbCr encoding. 120 * - ``V4L2_YCBCR_ENC_709`` 121 - Use the Rec. 709 Y'CbCr encoding. 122 * - ``V4L2_YCBCR_ENC_XV601`` 123 - Use the extended gamut xvYCC BT.601 encoding. 124 * - ``V4L2_YCBCR_ENC_XV709`` 125 - Use the extended gamut xvYCC Rec. 709 encoding. 126 * - ``V4L2_YCBCR_ENC_BT2020`` 127 - Use the default non-constant luminance BT.2020 Y'CbCr encoding. 128 * - ``V4L2_YCBCR_ENC_BT2020_CONST_LUM`` 129 - Use the constant luminance BT.2020 Yc'CbcCrc encoding. 130 * - ``V4L2_YCBCR_ENC_SMPTE_240M`` 131 - Use the SMPTE 240M Y'CbCr encoding. 132 133 134 135.. c:type:: v4l2_hsv_encoding 136 137.. tabularcolumns:: |p{6.5cm}|p{11.0cm}| 138 139.. flat-table:: V4L2 HSV Encodings 140 :header-rows: 1 141 :stub-columns: 0 142 143 * - Identifier 144 - Details 145 * - ``V4L2_HSV_ENC_180`` 146 - For the Hue, each LSB is two degrees. 147 * - ``V4L2_HSV_ENC_256`` 148 - For the Hue, the 360 degrees are mapped into 8 bits, i.e. each 149 LSB is roughly 1.41 degrees. 150 151 152 153.. c:type:: v4l2_quantization 154 155.. tabularcolumns:: |p{6.5cm}|p{11.0cm}| 156 157.. flat-table:: V4L2 Quantization Methods 158 :header-rows: 1 159 :stub-columns: 0 160 161 * - Identifier 162 - Details 163 * - ``V4L2_QUANTIZATION_DEFAULT`` 164 - Use the default quantization encoding as defined by the 165 colorspace. This is always full range for R'G'B' (except for the 166 BT.2020 colorspace) and HSV. It is usually limited range for Y'CbCr. 167 * - ``V4L2_QUANTIZATION_FULL_RANGE`` 168 - Use the full range quantization encoding. I.e. the range [0…1] is 169 mapped to [0…255] (with possible clipping to [1…254] to avoid the 170 0x00 and 0xff values). Cb and Cr are mapped from [-0.5…0.5] to 171 [0…255] (with possible clipping to [1…254] to avoid the 0x00 and 172 0xff values). 173 * - ``V4L2_QUANTIZATION_LIM_RANGE`` 174 - Use the limited range quantization encoding. I.e. the range [0…1] 175 is mapped to [16…235]. Cb and Cr are mapped from [-0.5…0.5] to 176 [16…240]. 177