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
177 scaled and offset according to the limited range formula:
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
190 scaled and offset according to the limited range formula:
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] and quantized without further scaling or offsets.
202 The non-standard xvYCC 709 or xvYCC 601 encodings can be
203 used by selecting ``V4L2_YCBCR_ENC_XV709`` or ``V4L2_YCBCR_ENC_XV601``.
204 As seen by the xvYCC formulas these encodings always use limited range quantization,
205 there is no full range variant. The whole point of these extended gamut encodings
206 is that values outside the limited range are still valid, although they
207 map to R', G' and B' values outside the [0…1] range and are therefore outside
208 the Rec. 709 colorspace gamut.
213 Colorspace sRGB (V4L2_COLORSPACE_SRGB)
214 ======================================
216 The :ref:`srgb` standard defines the colorspace used by most webcams
217 and computer graphics. The default transfer function is
218 ``V4L2_XFER_FUNC_SRGB``. The default Y'CbCr encoding is
219 ``V4L2_YCBCR_ENC_601``. The default Y'CbCr quantization is limited range.
221 Note that the :ref:`sycc` standard specifies full range quantization,
222 however all current capture hardware supported by the kernel convert
223 R'G'B' to limited range Y'CbCr. So choosing full range as the default
224 would break how applications interpret the quantization range.
226 The chromaticities of the primary colors and the white reference are:
230 .. tabularcolumns:: |p{4.4cm}|p{4.4cm}|p{8.7cm}|
232 .. flat-table:: sRGB Chromaticities
249 * - White Reference (D65)
254 These chromaticities are identical to the Rec. 709 colorspace.
256 Transfer function. Note that negative values for L are only used by the
261 L' = -1.055(-L)^{\frac{1}{2.4} } + 0.055\text{, for }L < -0.0031308
263 L' = 12.92L\text{, for }-0.0031308 \le L \le 0.0031308
265 L' = 1.055L ^{\frac{1}{2.4} } - 0.055\text{, for }0.0031308 < L \le 1
267 Inverse Transfer function:
271 L = -((-L' + 0.055) / 1.055) ^{2.4}\text{, for }L' < -0.04045
273 L = L' / 12.92\text{, for }-0.04045 \le L' \le 0.04045
275 L = ((L' + 0.055) / 1.055) ^{2.4}\text{, for }L' > 0.04045
277 The luminance (Y') and color difference (Cb and Cr) are obtained with
278 the following ``V4L2_YCBCR_ENC_601`` encoding as defined by :ref:`sycc`:
282 Y' = 0.2990R' + 0.5870G' + 0.1140B'
284 Cb = -0.1687R' - 0.3313G' + 0.5B'
286 Cr = 0.5R' - 0.4187G' - 0.0813B'
288 Y' is clamped to the range [0…1] and Cb and Cr are clamped to the range
289 [-0.5…0.5]. This transform is identical to one defined in SMPTE
290 170M/BT.601. The Y'CbCr quantization is limited range.
295 Colorspace Adobe RGB (V4L2_COLORSPACE_ADOBERGB)
296 ===============================================
298 The :ref:`adobergb` standard defines the colorspace used by computer
299 graphics that use the AdobeRGB colorspace. This is also known as the
300 :ref:`oprgb` standard. The default transfer function is
301 ``V4L2_XFER_FUNC_ADOBERGB``. The default Y'CbCr encoding is
302 ``V4L2_YCBCR_ENC_601``. The default Y'CbCr quantization is limited
305 Note that the :ref:`oprgb` standard specifies full range quantization,
306 however all current capture hardware supported by the kernel convert
307 R'G'B' to limited range Y'CbCr. So choosing full range as the default
308 would break how applications interpret the quantization range.
310 The chromaticities of the primary colors and the white reference are:
313 .. tabularcolumns:: |p{4.4cm}|p{4.4cm}|p{8.7cm}|
315 .. flat-table:: Adobe RGB Chromaticities
332 * - White Reference (D65)
342 L' = L ^{\frac{1}{2.19921875}}
344 Inverse Transfer function:
348 L = L'^{(2.19921875)}
350 The luminance (Y') and color difference (Cb and Cr) are obtained with
351 the following ``V4L2_YCBCR_ENC_601`` encoding:
355 Y' = 0.2990R' + 0.5870G' + 0.1140B'
357 Cb = -0.1687R' - 0.3313G' + 0.5B'
359 Cr = 0.5R' - 0.4187G' - 0.0813B'
361 Y' is clamped to the range [0…1] and Cb and Cr are clamped to the range
362 [-0.5…0.5]. This transform is identical to one defined in SMPTE
363 170M/BT.601. The Y'CbCr quantization is limited range.
368 Colorspace BT.2020 (V4L2_COLORSPACE_BT2020)
369 ===========================================
371 The :ref:`itu2020` standard defines the colorspace used by Ultra-high
372 definition television (UHDTV). The default transfer function is
373 ``V4L2_XFER_FUNC_709``. The default Y'CbCr encoding is
374 ``V4L2_YCBCR_ENC_BT2020``. The default R'G'B' quantization is limited
375 range (!), and so is the default Y'CbCr quantization. The chromaticities
376 of the primary colors and the white reference are:
380 .. tabularcolumns:: |p{4.4cm}|p{4.4cm}|p{8.7cm}|
382 .. flat-table:: BT.2020 Chromaticities
399 * - White Reference (D65)
405 Transfer function (same as Rec. 709):
409 L' = 4.5L\text{, for }0 \le L < 0.018
411 L' = 1.099L ^{0.45} - 0.099\text{, for } 0.018 \le L \le 1
413 Inverse Transfer function:
417 L = L' / 4.5\text{, for } L' < 0.081
419 L = \left( \frac{L' + 0.099}{1.099}\right) ^{\frac{1}{0.45} }\text{, for } L' \ge 0.081
421 The luminance (Y') and color difference (Cb and Cr) are obtained with
422 the following ``V4L2_YCBCR_ENC_BT2020`` encoding:
426 Y' = 0.2627R' + 0.6780G' + 0.0593B'
428 Cb = -0.1396R' - 0.3604G' + 0.5B'
430 Cr = 0.5R' - 0.4598G' - 0.0402B'
432 Y' is clamped to the range [0…1] and Cb and Cr are clamped to the range
433 [-0.5…0.5]. The Y'CbCr quantization is limited range.
435 There is also an alternate constant luminance R'G'B' to Yc'CbcCrc
436 (``V4L2_YCBCR_ENC_BT2020_CONST_LUM``) encoding:
444 Yc' = (0.2627R + 0.6780G + 0.0593B)'& \\
446 &Cbc = (B' - Yc') / 1.9404 \\
448 &Cbc = (B' - Yc') / 1.5816 \\
450 &Crc = (R' - Y') / 1.7184 \\
452 &Crc = (R' - Y') / 0.9936
455 Yc' is clamped to the range [0…1] and Cbc and Crc are clamped to the
456 range [-0.5…0.5]. The Yc'CbcCrc quantization is limited range.
461 Colorspace DCI-P3 (V4L2_COLORSPACE_DCI_P3)
462 ==========================================
464 The :ref:`smpte431` standard defines the colorspace used by cinema
465 projectors that use the DCI-P3 colorspace. The default transfer function
466 is ``V4L2_XFER_FUNC_DCI_P3``. The default Y'CbCr encoding is
467 ``V4L2_YCBCR_ENC_709``. The default Y'CbCr quantization is limited range.
471 Note that this colorspace standard does not specify a
472 Y'CbCr encoding since it is not meant to be encoded to Y'CbCr. So this
473 default Y'CbCr encoding was picked because it is the HDTV encoding.
475 The chromaticities of the primary colors and the white reference are:
479 .. tabularcolumns:: |p{4.4cm}|p{4.4cm}|p{8.7cm}|
481 .. flat-table:: DCI-P3 Chromaticities
508 L' = L^{\frac{1}{2.6}}
510 Inverse Transfer function:
516 Y'CbCr encoding is not specified. V4L2 defaults to Rec. 709.
521 Colorspace SMPTE 240M (V4L2_COLORSPACE_SMPTE240M)
522 =================================================
524 The :ref:`smpte240m` standard was an interim standard used during the
525 early days of HDTV (1988-1998). It has been superseded by Rec. 709. The
526 default transfer function is ``V4L2_XFER_FUNC_SMPTE240M``. The default
527 Y'CbCr encoding is ``V4L2_YCBCR_ENC_SMPTE240M``. The default Y'CbCr
528 quantization is limited range. The chromaticities of the primary colors
529 and the white reference are:
533 .. tabularcolumns:: |p{4.4cm}|p{4.4cm}|p{8.7cm}|
535 .. flat-table:: SMPTE 240M Chromaticities
552 * - White Reference (D65)
557 These chromaticities are identical to the SMPTE 170M colorspace.
563 L' = 4L\text{, for } 0 \le L < 0.0228
565 L' = 1.1115L ^{0.45} - 0.1115\text{, for } 0.0228 \le L \le 1
567 Inverse Transfer function:
571 L = \frac{L'}{4}\text{, for } 0 \le L' < 0.0913
573 L = \left( \frac{L' + 0.1115}{1.1115}\right) ^{\frac{1}{0.45} }\text{, for } L' \ge 0.0913
575 The luminance (Y') and color difference (Cb and Cr) are obtained with
576 the following ``V4L2_YCBCR_ENC_SMPTE240M`` encoding:
580 Y' = 0.2122R' + 0.7013G' + 0.0865B'
582 Cb = -0.1161R' - 0.3839G' + 0.5B'
584 Cr = 0.5R' - 0.4451G' - 0.0549B'
586 Y' is clamped to the range [0…1] and Cb and Cr are clamped to the
587 range [-0.5…0.5]. The Y'CbCr quantization is limited range.
592 Colorspace NTSC 1953 (V4L2_COLORSPACE_470_SYSTEM_M)
593 ===================================================
595 This standard defines the colorspace used by NTSC in 1953. In practice
596 this colorspace is obsolete and SMPTE 170M should be used instead. The
597 default transfer function is ``V4L2_XFER_FUNC_709``. The default Y'CbCr
598 encoding is ``V4L2_YCBCR_ENC_601``. The default Y'CbCr quantization is
599 limited range. The chromaticities of the primary colors and the white
604 .. tabularcolumns:: |p{4.4cm}|p{4.4cm}|p{8.7cm}|
606 .. flat-table:: NTSC 1953 Chromaticities
623 * - White Reference (C)
630 This colorspace uses Illuminant C instead of D65 as the white
631 reference. To correctly convert an image in this colorspace to another
632 that uses D65 you need to apply a chromatic adaptation algorithm such as
635 The transfer function was never properly defined for NTSC 1953. The Rec.
636 709 transfer function is recommended in the literature:
640 L' = 4.5L\text{, for } 0 \le L < 0.018
642 L' = 1.099L ^{0.45} - 0.099\text{, for } 0.018 \le L \le 1
644 Inverse Transfer function:
648 L = \frac{L'}{4.5} \text{, for } L' < 0.081
650 L = \left( \frac{L' + 0.099}{1.099}\right) ^{\frac{1}{0.45} }\text{, for } L' \ge 0.081
652 The luminance (Y') and color difference (Cb and Cr) are obtained with
653 the following ``V4L2_YCBCR_ENC_601`` encoding:
657 Y' = 0.2990R' + 0.5870G' + 0.1140B'
659 Cb = -0.1687R' - 0.3313G' + 0.5B'
661 Cr = 0.5R' - 0.4187G' - 0.0813B'
663 Y' is clamped to the range [0…1] and Cb and Cr are clamped to the range
664 [-0.5…0.5]. The Y'CbCr quantization is limited range. This transform is
665 identical to one defined in SMPTE 170M/BT.601.
670 Colorspace EBU Tech. 3213 (V4L2_COLORSPACE_470_SYSTEM_BG)
671 =========================================================
673 The :ref:`tech3213` standard defines the colorspace used by PAL/SECAM
674 in 1975. In practice this colorspace is obsolete and SMPTE 170M should
675 be used instead. The default transfer function is
676 ``V4L2_XFER_FUNC_709``. The default Y'CbCr encoding is
677 ``V4L2_YCBCR_ENC_601``. The default Y'CbCr quantization is limited
678 range. The chromaticities of the primary colors and the white reference
683 .. tabularcolumns:: |p{4.4cm}|p{4.4cm}|p{8.7cm}|
685 .. flat-table:: EBU Tech. 3213 Chromaticities
702 * - White Reference (D65)
708 The transfer function was never properly defined for this colorspace.
709 The Rec. 709 transfer function is recommended in the literature:
713 L' = 4.5L\text{, for } 0 \le L < 0.018
715 L' = 1.099L ^{0.45} - 0.099\text{, for } 0.018 \le L \le 1
717 Inverse Transfer function:
721 L = \frac{L'}{4.5} \text{, for } L' < 0.081
723 L = \left(\frac{L' + 0.099}{1.099} \right) ^{\frac{1}{0.45} }\text{, for } L' \ge 0.081
725 The luminance (Y') and color difference (Cb and Cr) are obtained with
726 the following ``V4L2_YCBCR_ENC_601`` encoding:
730 Y' = 0.2990R' + 0.5870G' + 0.1140B'
732 Cb = -0.1687R' - 0.3313G' + 0.5B'
734 Cr = 0.5R' - 0.4187G' - 0.0813B'
736 Y' is clamped to the range [0…1] and Cb and Cr are clamped to the range
737 [-0.5…0.5]. The Y'CbCr quantization is limited range. This transform is
738 identical to one defined in SMPTE 170M/BT.601.
743 Colorspace JPEG (V4L2_COLORSPACE_JPEG)
744 ======================================
746 This colorspace defines the colorspace used by most (Motion-)JPEG
747 formats. The chromaticities of the primary colors and the white
748 reference are identical to sRGB. The transfer function use is
749 ``V4L2_XFER_FUNC_SRGB``. The Y'CbCr encoding is ``V4L2_YCBCR_ENC_601``
750 with full range quantization where Y' is scaled to [0…255] and Cb/Cr are
751 scaled to [-128…128] and then clipped to [-128…127].
755 The JPEG standard does not actually store colorspace
756 information. So if something other than sRGB is used, then the driver
757 will have to set that information explicitly. Effectively
758 ``V4L2_COLORSPACE_JPEG`` can be considered to be an abbreviation for
759 ``V4L2_COLORSPACE_SRGB``, ``V4L2_YCBCR_ENC_601`` and
760 ``V4L2_QUANTIZATION_FULL_RANGE``.