colorspaces-defs.rst

  1.. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later
  2.. c:namespace:: V4L
  3
  4****************************
  5Defining Colorspaces in V4L2
  6****************************
  7
  8In V4L2 colorspaces are defined by four values. The first is the
  9colorspace identifier (enum :c:type:`v4l2_colorspace`)
 10which defines the chromaticities, the default transfer function, the
 11default Y'CbCr encoding and the default quantization method. The second
 12is the transfer function identifier (enum
 13:c:type:`v4l2_xfer_func`) to specify non-standard
 14transfer functions. The third is the Y'CbCr encoding identifier (enum
 15:c:type:`v4l2_ycbcr_encoding`) to specify
 16non-standard Y'CbCr encodings and the fourth is the quantization
 17identifier (enum :c:type:`v4l2_quantization`) to
 18specify non-standard quantization methods. Most of the time only the
 19colorspace field of struct :c:type:`v4l2_pix_format`
 20or struct :c:type:`v4l2_pix_format_mplane`
 21needs to be filled in.
 22
 23.. _hsv-colorspace:
 24
 25On :ref:`HSV formats <hsv-formats>` the *Hue* is defined as the angle on
 26the cylindrical color representation. Usually this angle is measured in
 27degrees, i.e. 0-360. When we map this angle value into 8 bits, there are
 28two basic ways to do it: Divide the angular value by 2 (0-179), or use the
 29whole range, 0-255, dividing the angular value by 1.41. The enum
 30:c:type:`v4l2_hsv_encoding` specifies which encoding is used.
 31
 32.. note:: The default R'G'B' quantization is full range for all
 33   colorspaces. HSV formats are always full range.
 34
 35.. tabularcolumns:: |p{6.7cm}|p{10.8cm}|
 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{7.2cm}|p{10.3cm}|
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' and HSV.
166	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]. Limited Range cannot be used with HSV.