1 .. -*- coding: utf-8; mode: rst -*-
3 ********************************
4 Detailed Colorspace Descriptions
5 ********************************
10 Colorspace SMPTE 170M (V4L2_COLORSPACE_SMPTE170M)
11 =================================================
13 The :ref:`smpte170m` standard defines the colorspace used by NTSC and
14 PAL and by SDTV in general. The default transfer function is
15 ``V4L2_XFER_FUNC_709``. The default Y'CbCr encoding is
16 ``V4L2_YCBCR_ENC_601``. The default Y'CbCr quantization is limited
17 range. The chromaticities of the primary colors and the white reference
22 .. tabularcolumns:: |p{4.4cm}|p{4.4cm}|p{8.7cm}|
24 .. flat-table:: SMPTE 170M Chromaticities
41 * - White Reference (D65)
46 The red, green and blue chromaticities are also often referred to as the
47 SMPTE C set, so this colorspace is sometimes called SMPTE C as well.
49 The transfer function defined for SMPTE 170M is the same as the one
54 L' = -1.099(-L)^{0.45} + 0.099 \text{, for } L \le-0.018
56 L' = 4.5L \text{, for } -0.018 < L < 0.018
58 L' = 1.099L^{0.45} - 0.099 \text{, for } L \ge 0.018
60 Inverse Transfer function:
64 L = -\left( \frac{L' - 0.099}{-1.099} \right) ^{\frac{1}{0.45}} \text{, for } L' \le -0.081
66 L = \frac{L'}{4.5} \text{, for } -0.081 < L' < 0.081
68 L = \left(\frac{L' + 0.099}{1.099}\right)^{\frac{1}{0.45} } \text{, for } L' \ge 0.081
70 The luminance (Y') and color difference (Cb and Cr) are obtained with
71 the following ``V4L2_YCBCR_ENC_601`` encoding:
75 Y' = 0.2990R' + 0.5870G' + 0.1140B'
77 Cb = -0.1687R' - 0.3313G' + 0.5B'
79 Cr = 0.5R' - 0.4187G' - 0.0813B'
81 Y' is clamped to the range [0…1] and Cb and Cr are clamped to the range
82 [-0.5…0.5]. This conversion to Y'CbCr is identical to the one defined in
83 the :ref:`itu601` standard and this colorspace is sometimes called
84 BT.601 as well, even though BT.601 does not mention any color primaries.
86 The default quantization is limited range, but full range is possible
92 Colorspace Rec. 709 (V4L2_COLORSPACE_REC709)
93 ============================================
95 The :ref:`itu709` standard defines the colorspace used by HDTV in
96 general. The default transfer function is ``V4L2_XFER_FUNC_709``. The
97 default Y'CbCr encoding is ``V4L2_YCBCR_ENC_709``. The default Y'CbCr
98 quantization is limited range. The chromaticities of the primary colors
99 and the white reference are:
103 .. tabularcolumns:: |p{4.4cm}|p{4.4cm}|p{8.7cm}|
105 .. flat-table:: Rec. 709 Chromaticities
122 * - White Reference (D65)
127 The full name of this standard is Rec. ITU-R BT.709-5.
129 Transfer function. Normally L is in the range [0…1], but for the
130 extended gamut xvYCC encoding values outside that range are allowed.
134 L' = -1.099(-L)^{0.45} + 0.099 \text{, for } L \le -0.018
136 L' = 4.5L \text{, for } -0.018 < L < 0.018
138 L' = 1.099L^{0.45} - 0.099 \text{, for } L \ge 0.018
140 Inverse Transfer function:
144 L = -\left( \frac{L' - 0.099}{-1.099} \right)^\frac{1}{0.45} \text{, for } L' \le -0.081
146 L = \frac{L'}{4.5}\text{, for } -0.081 < L' < 0.081
148 L = \left(\frac{L' + 0.099}{1.099}\right)^{\frac{1}{0.45} } \text{, for } L' \ge 0.081
150 The luminance (Y') and color difference (Cb and Cr) are obtained with
151 the following ``V4L2_YCBCR_ENC_709`` encoding:
155 Y' = 0.2126R' + 0.7152G' + 0.0722B'
157 Cb = -0.1146R' - 0.3854G' + 0.5B'
159 Cr = 0.5R' - 0.4542G' - 0.0458B'
161 Y' is clamped to the range [0…1] and Cb and Cr are clamped to the range
164 The default quantization is limited range, but full range is possible
165 although rarely seen.
167 The ``V4L2_YCBCR_ENC_709`` encoding described above is the default for
168 this colorspace, but it can be overridden with ``V4L2_YCBCR_ENC_601``,
169 in which case the BT.601 Y'CbCr encoding is used.
171 Two additional extended gamut Y'CbCr encodings are also possible with
174 The xvYCC 709 encoding (``V4L2_YCBCR_ENC_XV709``, :ref:`xvycc`) is
175 similar to the Rec. 709 encoding, but it allows for R', G' and B' values
176 that are outside the range [0…1]. The resulting Y', Cb and Cr values are
181 Y' = \frac{219}{256} * (0.2126R' + 0.7152G' + 0.0722B') + \frac{16}{256}
183 Cb = \frac{224}{256} * (-0.1146R' - 0.3854G' + 0.5B')
185 Cr = \frac{224}{256} * (0.5R' - 0.4542G' - 0.0458B')
187 The xvYCC 601 encoding (``V4L2_YCBCR_ENC_XV601``, :ref:`xvycc`) is
188 similar to the BT.601 encoding, but it allows for R', G' and B' values
189 that are outside the range [0…1]. The resulting Y', Cb and Cr values are
194 Y' = \frac{219}{256} * (0.2990R' + 0.5870G' + 0.1140B') + \frac{16}{256}
196 Cb = \frac{224}{256} * (-0.1687R' - 0.3313G' + 0.5B')
198 Cr = \frac{224}{256} * (0.5R' - 0.4187G' - 0.0813B')
200 Y' is clamped to the range [0…1] and Cb and Cr are clamped to the range
201 [-0.5…0.5]. The non-standard xvYCC 709 or xvYCC 601 encodings can be
202 used by selecting ``V4L2_YCBCR_ENC_XV709`` or ``V4L2_YCBCR_ENC_XV601``.
203 The xvYCC encodings always use full range quantization.
208 Colorspace sRGB (V4L2_COLORSPACE_SRGB)
209 ======================================
211 The :ref:`srgb` standard defines the colorspace used by most webcams
212 and computer graphics. The default transfer function is
213 ``V4L2_XFER_FUNC_SRGB``. The default Y'CbCr encoding is
214 ``V4L2_YCBCR_ENC_601``. The default Y'CbCr quantization is limited range.
216 Note that the :ref:`sycc` standard specifies full range quantization,
217 however all current capture hardware supported by the kernel convert
218 R'G'B' to limited range Y'CbCr. So choosing full range as the default
219 would break how applications interpret the quantization range.
221 The chromaticities of the primary colors and the white reference are:
225 .. tabularcolumns:: |p{4.4cm}|p{4.4cm}|p{8.7cm}|
227 .. flat-table:: sRGB Chromaticities
244 * - White Reference (D65)
249 These chromaticities are identical to the Rec. 709 colorspace.
251 Transfer function. Note that negative values for L are only used by the
256 L' = -1.055(-L)^{\frac{1}{2.4} } + 0.055\text{, for }L < -0.0031308
258 L' = 12.92L\text{, for }-0.0031308 \le L \le 0.0031308
260 L' = 1.055L ^{\frac{1}{2.4} } - 0.055\text{, for }0.0031308 < L \le 1
262 Inverse Transfer function:
266 L = -((-L' + 0.055) / 1.055) ^{2.4}\text{, for }L' < -0.04045
268 L = L' / 12.92\text{, for }-0.04045 \le L' \le 0.04045
270 L = ((L' + 0.055) / 1.055) ^{2.4}\text{, for }L' > 0.04045
272 The luminance (Y') and color difference (Cb and Cr) are obtained with
273 the following ``V4L2_YCBCR_ENC_601`` encoding as defined by :ref:`sycc`:
277 Y' = 0.2990R' + 0.5870G' + 0.1140B'
279 Cb = -0.1687R' - 0.3313G' + 0.5B'
281 Cr = 0.5R' - 0.4187G' - 0.0813B'
283 Y' is clamped to the range [0…1] and Cb and Cr are clamped to the range
284 [-0.5…0.5]. This transform is identical to one defined in SMPTE
285 170M/BT.601. The Y'CbCr quantization is limited range.
290 Colorspace Adobe RGB (V4L2_COLORSPACE_ADOBERGB)
291 ===============================================
293 The :ref:`adobergb` standard defines the colorspace used by computer
294 graphics that use the AdobeRGB colorspace. This is also known as the
295 :ref:`oprgb` standard. The default transfer function is
296 ``V4L2_XFER_FUNC_ADOBERGB``. The default Y'CbCr encoding is
297 ``V4L2_YCBCR_ENC_601``. The default Y'CbCr quantization is limited
300 Note that the :ref:`oprgb` standard specifies full range quantization,
301 however all current capture hardware supported by the kernel convert
302 R'G'B' to limited range Y'CbCr. So choosing full range as the default
303 would break how applications interpret the quantization range.
305 The chromaticities of the primary colors and the white reference are:
308 .. tabularcolumns:: |p{4.4cm}|p{4.4cm}|p{8.7cm}|
310 .. flat-table:: Adobe RGB Chromaticities
327 * - White Reference (D65)
337 L' = L ^{\frac{1}{2.19921875}}
339 Inverse Transfer function:
343 L = L'^{(2.19921875)}
345 The luminance (Y') and color difference (Cb and Cr) are obtained with
346 the following ``V4L2_YCBCR_ENC_601`` encoding:
350 Y' = 0.2990R' + 0.5870G' + 0.1140B'
352 Cb = -0.1687R' - 0.3313G' + 0.5B'
354 Cr = 0.5R' - 0.4187G' - 0.0813B'
356 Y' is clamped to the range [0…1] and Cb and Cr are clamped to the range
357 [-0.5…0.5]. This transform is identical to one defined in SMPTE
358 170M/BT.601. The Y'CbCr quantization is limited range.
363 Colorspace BT.2020 (V4L2_COLORSPACE_BT2020)
364 ===========================================
366 The :ref:`itu2020` standard defines the colorspace used by Ultra-high
367 definition television (UHDTV). The default transfer function is
368 ``V4L2_XFER_FUNC_709``. The default Y'CbCr encoding is
369 ``V4L2_YCBCR_ENC_BT2020``. The default R'G'B' quantization is limited
370 range (!), and so is the default Y'CbCr quantization. The chromaticities
371 of the primary colors and the white reference are:
375 .. tabularcolumns:: |p{4.4cm}|p{4.4cm}|p{8.7cm}|
377 .. flat-table:: BT.2020 Chromaticities
394 * - White Reference (D65)
400 Transfer function (same as Rec. 709):
404 L' = 4.5L\text{, for }0 \le L < 0.018
406 L' = 1.099L ^{0.45} - 0.099\text{, for } 0.018 \le L \le 1
408 Inverse Transfer function:
412 L = L' / 4.5\text{, for } L' < 0.081
414 L = \left( \frac{L' + 0.099}{1.099}\right) ^{\frac{1}{0.45} }\text{, for } L' \ge 0.081
416 The luminance (Y') and color difference (Cb and Cr) are obtained with
417 the following ``V4L2_YCBCR_ENC_BT2020`` encoding:
421 Y' = 0.2627R' + 0.6780G' + 0.0593B'
423 Cb = -0.1396R' - 0.3604G' + 0.5B'
425 Cr = 0.5R' - 0.4598G' - 0.0402B'
427 Y' is clamped to the range [0…1] and Cb and Cr are clamped to the range
428 [-0.5…0.5]. The Y'CbCr quantization is limited range.
430 There is also an alternate constant luminance R'G'B' to Yc'CbcCrc
431 (``V4L2_YCBCR_ENC_BT2020_CONST_LUM``) encoding:
439 Yc' = (0.2627R + 0.6780G + 0.0593B)'& \\
441 &Cbc = (B' - Yc') / 1.9404 \\
443 &Cbc = (B' - Yc') / 1.5816 \\
445 &Crc = (R' - Y') / 1.7184 \\
447 &Crc = (R' - Y') / 0.9936
450 Yc' is clamped to the range [0…1] and Cbc and Crc are clamped to the
451 range [-0.5…0.5]. The Yc'CbcCrc quantization is limited range.
456 Colorspace DCI-P3 (V4L2_COLORSPACE_DCI_P3)
457 ==========================================
459 The :ref:`smpte431` standard defines the colorspace used by cinema
460 projectors that use the DCI-P3 colorspace. The default transfer function
461 is ``V4L2_XFER_FUNC_DCI_P3``. The default Y'CbCr encoding is
462 ``V4L2_YCBCR_ENC_709``. The default Y'CbCr quantization is limited range.
466 Note that this colorspace standard does not specify a
467 Y'CbCr encoding since it is not meant to be encoded to Y'CbCr. So this
468 default Y'CbCr encoding was picked because it is the HDTV encoding.
470 The chromaticities of the primary colors and the white reference are:
474 .. tabularcolumns:: |p{4.4cm}|p{4.4cm}|p{8.7cm}|
476 .. flat-table:: DCI-P3 Chromaticities
503 L' = L^{\frac{1}{2.6}}
505 Inverse Transfer function:
511 Y'CbCr encoding is not specified. V4L2 defaults to Rec. 709.
516 Colorspace SMPTE 240M (V4L2_COLORSPACE_SMPTE240M)
517 =================================================
519 The :ref:`smpte240m` standard was an interim standard used during the
520 early days of HDTV (1988-1998). It has been superseded by Rec. 709. The
521 default transfer function is ``V4L2_XFER_FUNC_SMPTE240M``. The default
522 Y'CbCr encoding is ``V4L2_YCBCR_ENC_SMPTE240M``. The default Y'CbCr
523 quantization is limited range. The chromaticities of the primary colors
524 and the white reference are:
528 .. tabularcolumns:: |p{4.4cm}|p{4.4cm}|p{8.7cm}|
530 .. flat-table:: SMPTE 240M Chromaticities
547 * - White Reference (D65)
552 These chromaticities are identical to the SMPTE 170M colorspace.
558 L' = 4L\text{, for } 0 \le L < 0.0228
560 L' = 1.1115L ^{0.45} - 0.1115\text{, for } 0.0228 \le L \le 1
562 Inverse Transfer function:
566 L = \frac{L'}{4}\text{, for } 0 \le L' < 0.0913
568 L = \left( \frac{L' + 0.1115}{1.1115}\right) ^{\frac{1}{0.45} }\text{, for } L' \ge 0.0913
570 The luminance (Y') and color difference (Cb and Cr) are obtained with
571 the following ``V4L2_YCBCR_ENC_SMPTE240M`` encoding:
575 Y' = 0.2122R' + 0.7013G' + 0.0865B'
577 Cb = -0.1161R' - 0.3839G' + 0.5B'
579 Cr = 0.5R' - 0.4451G' - 0.0549B'
581 Y' is clamped to the range [0…1] and Cb and Cr are clamped to the
582 range [-0.5…0.5]. The Y'CbCr quantization is limited range.
587 Colorspace NTSC 1953 (V4L2_COLORSPACE_470_SYSTEM_M)
588 ===================================================
590 This standard defines the colorspace used by NTSC in 1953. In practice
591 this colorspace is obsolete and SMPTE 170M should be used instead. The
592 default transfer function is ``V4L2_XFER_FUNC_709``. The default Y'CbCr
593 encoding is ``V4L2_YCBCR_ENC_601``. The default Y'CbCr quantization is
594 limited range. The chromaticities of the primary colors and the white
599 .. tabularcolumns:: |p{4.4cm}|p{4.4cm}|p{8.7cm}|
601 .. flat-table:: NTSC 1953 Chromaticities
618 * - White Reference (C)
625 This colorspace uses Illuminant C instead of D65 as the white
626 reference. To correctly convert an image in this colorspace to another
627 that uses D65 you need to apply a chromatic adaptation algorithm such as
630 The transfer function was never properly defined for NTSC 1953. The Rec.
631 709 transfer function is recommended in the literature:
635 L' = 4.5L\text{, for } 0 \le L < 0.018
637 L' = 1.099L ^{0.45} - 0.099\text{, for } 0.018 \le L \le 1
639 Inverse Transfer function:
643 L = \frac{L'}{4.5} \text{, for } L' < 0.081
645 L = \left( \frac{L' + 0.099}{1.099}\right) ^{\frac{1}{0.45} }\text{, for } L' \ge 0.081
647 The luminance (Y') and color difference (Cb and Cr) are obtained with
648 the following ``V4L2_YCBCR_ENC_601`` encoding:
652 Y' = 0.2990R' + 0.5870G' + 0.1140B'
654 Cb = -0.1687R' - 0.3313G' + 0.5B'
656 Cr = 0.5R' - 0.4187G' - 0.0813B'
658 Y' is clamped to the range [0…1] and Cb and Cr are clamped to the range
659 [-0.5…0.5]. The Y'CbCr quantization is limited range. This transform is
660 identical to one defined in SMPTE 170M/BT.601.
665 Colorspace EBU Tech. 3213 (V4L2_COLORSPACE_470_SYSTEM_BG)
666 =========================================================
668 The :ref:`tech3213` standard defines the colorspace used by PAL/SECAM
669 in 1975. In practice this colorspace is obsolete and SMPTE 170M should
670 be used instead. The default transfer function is
671 ``V4L2_XFER_FUNC_709``. The default Y'CbCr encoding is
672 ``V4L2_YCBCR_ENC_601``. The default Y'CbCr quantization is limited
673 range. The chromaticities of the primary colors and the white reference
678 .. tabularcolumns:: |p{4.4cm}|p{4.4cm}|p{8.7cm}|
680 .. flat-table:: EBU Tech. 3213 Chromaticities
697 * - White Reference (D65)
703 The transfer function was never properly defined for this colorspace.
704 The Rec. 709 transfer function is recommended in the literature:
708 L' = 4.5L\text{, for } 0 \le L < 0.018
710 L' = 1.099L ^{0.45} - 0.099\text{, for } 0.018 \le L \le 1
712 Inverse Transfer function:
716 L = \frac{L'}{4.5} \text{, for } L' < 0.081
718 L = \left(\frac{L' + 0.099}{1.099} \right) ^{\frac{1}{0.45} }\text{, for } L' \ge 0.081
720 The luminance (Y') and color difference (Cb and Cr) are obtained with
721 the following ``V4L2_YCBCR_ENC_601`` encoding:
725 Y' = 0.2990R' + 0.5870G' + 0.1140B'
727 Cb = -0.1687R' - 0.3313G' + 0.5B'
729 Cr = 0.5R' - 0.4187G' - 0.0813B'
731 Y' is clamped to the range [0…1] and Cb and Cr are clamped to the range
732 [-0.5…0.5]. The Y'CbCr quantization is limited range. This transform is
733 identical to one defined in SMPTE 170M/BT.601.
738 Colorspace JPEG (V4L2_COLORSPACE_JPEG)
739 ======================================
741 This colorspace defines the colorspace used by most (Motion-)JPEG
742 formats. The chromaticities of the primary colors and the white
743 reference are identical to sRGB. The transfer function use is
744 ``V4L2_XFER_FUNC_SRGB``. The Y'CbCr encoding is ``V4L2_YCBCR_ENC_601``
745 with full range quantization where Y' is scaled to [0…255] and Cb/Cr are
746 scaled to [-128…128] and then clipped to [-128…127].
750 The JPEG standard does not actually store colorspace
751 information. So if something other than sRGB is used, then the driver
752 will have to set that information explicitly. Effectively
753 ``V4L2_COLORSPACE_JPEG`` can be considered to be an abbreviation for
754 ``V4L2_COLORSPACE_SRGB``, ``V4L2_YCBCR_ENC_601`` and
755 ``V4L2_QUANTIZATION_FULL_RANGE``.