Documentation/media/uapi/v4l/pixfmt-007.rst

   1 .. -*- coding: utf-8; mode: rst -*-
   2
   3 ********************************
   4 Detailed Colorspace Descriptions
   5 ********************************
   6
   7
   8 .. _col-smpte-170m:
   9
  10 Colorspace SMPTE 170M (V4L2_COLORSPACE_SMPTE170M)
  11 =================================================
  12
  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
  18 are:
  19
  20
  21
  22 .. tabularcolumns:: |p{4.4cm}|p{4.4cm}|p{8.7cm}|
  23
  24 .. flat-table:: SMPTE 170M Chromaticities
  25     :header-rows:  1
  26     :stub-columns: 0
  27     :widths:       1 1 2
  28
  29
  30     -  .. row 1
  31
  32        -  Color
  33
  34        -  x
  35
  36        -  y
  37
  38     -  .. row 2
  39
  40        -  Red
  41
  42        -  0.630
  43
  44        -  0.340
  45
  46     -  .. row 3
  47
  48        -  Green
  49
  50        -  0.310
  51
  52        -  0.595
  53
  54     -  .. row 4
  55
  56        -  Blue
  57
  58        -  0.155
  59
  60        -  0.070
  61
  62     -  .. row 5
  63
  64        -  White Reference (D65)
  65
  66        -  0.3127
  67
  68        -  0.3290
  69
  70
  71 The red, green and blue chromaticities are also often referred to as the
  72 SMPTE C set, so this colorspace is sometimes called SMPTE C as well.
  73
  74 The transfer function defined for SMPTE 170M is the same as the one
  75 defined in Rec. 709.
  76
  77 .. math::
  78
  79     L' = -1.099(-L)^{0.45} + 0.099 \text{, for } L \le-0.018
  80
  81     L' = 4.5L \text{, for } -0.018 < L < 0.018
  82
  83     L' = 1.099L^{0.45} - 0.099 \text{, for } L \ge 0.018
  84
  85 Inverse Transfer function:
  86
  87 .. math::
  88
  89     L = -\left( \frac{L' - 0.099}{-1.099} \right) ^{\frac{1}{0.45}} \text{, for } L' \le -0.081
  90
  91     L = \frac{L'}{4.5} \text{, for } -0.081 < L' < 0.081
  92
  93     L = \left(\frac{L' + 0.099}{1.099}\right)^{\frac{1}{0.45} } \text{, for } L' \ge 0.081
  94
  95 The luminance (Y') and color difference (Cb and Cr) are obtained with
  96 the following ``V4L2_YCBCR_ENC_601`` encoding:
  97
  98 .. math::
  99
 100     Y' = 0.2990R' + 0.5870G' + 0.1140B'
 101
 102     Cb = -0.1687R' - 0.3313G' + 0.5B'
 103
 104     Cr = 0.5R' - 0.4187G' - 0.0813B'
 105
 106 Y' is clamped to the range [0…1] and Cb and Cr are clamped to the range
 107 [-0.5…0.5]. This conversion to Y'CbCr is identical to the one defined in
 108 the :ref:`itu601` standard and this colorspace is sometimes called
 109 BT.601 as well, even though BT.601 does not mention any color primaries.
 110
 111 The default quantization is limited range, but full range is possible
 112 although rarely seen.
 113
 114
 115 .. _col-rec709:
 116
 117 Colorspace Rec. 709 (V4L2_COLORSPACE_REC709)
 118 ============================================
 119
 120 The :ref:`itu709` standard defines the colorspace used by HDTV in
 121 general. The default transfer function is ``V4L2_XFER_FUNC_709``. The
 122 default Y'CbCr encoding is ``V4L2_YCBCR_ENC_709``. The default Y'CbCr
 123 quantization is limited range. The chromaticities of the primary colors
 124 and the white reference are:
 125
 126
 127
 128 .. tabularcolumns:: |p{4.4cm}|p{4.4cm}|p{8.7cm}|
 129
 130 .. flat-table:: Rec. 709 Chromaticities
 131     :header-rows:  1
 132     :stub-columns: 0
 133     :widths:       1 1 2
 134
 135
 136     -  .. row 1
 137
 138        -  Color
 139
 140        -  x
 141
 142        -  y
 143
 144     -  .. row 2
 145
 146        -  Red
 147
 148        -  0.640
 149
 150        -  0.330
 151
 152     -  .. row 3
 153
 154        -  Green
 155
 156        -  0.300
 157
 158        -  0.600
 159
 160     -  .. row 4
 161
 162        -  Blue
 163
 164        -  0.150
 165
 166        -  0.060
 167
 168     -  .. row 5
 169
 170        -  White Reference (D65)
 171
 172        -  0.3127
 173
 174        -  0.3290
 175
 176
 177 The full name of this standard is Rec. ITU-R BT.709-5.
 178
 179 Transfer function. Normally L is in the range [0…1], but for the
 180 extended gamut xvYCC encoding values outside that range are allowed.
 181
 182 .. math::
 183
 184     L' = -1.099(-L)^{0.45} + 0.099 \text{, for } L \le -0.018
 185
 186     L' = 4.5L \text{, for } -0.018 < L < 0.018
 187
 188     L' = 1.099L^{0.45} - 0.099 \text{, for } L \ge 0.018
 189
 190 Inverse Transfer function:
 191
 192 .. math::
 193
 194     L = -\left( \frac{L' - 0.099}{-1.099} \right)^\frac{1}{0.45} \text{, for } L' \le -0.081
 195
 196     L = \frac{L'}{4.5}\text{, for } -0.081 < L' < 0.081
 197
 198     L = \left(\frac{L' + 0.099}{1.099}\right)^{\frac{1}{0.45} } \text{, for } L' \ge 0.081
 199
 200 The luminance (Y') and color difference (Cb and Cr) are obtained with
 201 the following ``V4L2_YCBCR_ENC_709`` encoding:
 202
 203 .. math::
 204
 205     Y' = 0.2126R' + 0.7152G' + 0.0722B'
 206
 207     Cb = -0.1146R' - 0.3854G' + 0.5B'
 208
 209     Cr = 0.5R' - 0.4542G' - 0.0458B'
 210
 211 Y' is clamped to the range [0…1] and Cb and Cr are clamped to the range
 212 [-0.5…0.5].
 213
 214 The default quantization is limited range, but full range is possible
 215 although rarely seen.
 216
 217 The ``V4L2_YCBCR_ENC_709`` encoding described above is the default for
 218 this colorspace, but it can be overridden with ``V4L2_YCBCR_ENC_601``,
 219 in which case the BT.601 Y'CbCr encoding is used.
 220
 221 Two additional extended gamut Y'CbCr encodings are also possible with
 222 this colorspace:
 223
 224 The xvYCC 709 encoding (``V4L2_YCBCR_ENC_XV709``, :ref:`xvycc`) is
 225 similar to the Rec. 709 encoding, but it allows for R', G' and B' values
 226 that are outside the range [0…1]. The resulting Y', Cb and Cr values are
 227 scaled and offset:
 228
 229 .. math::
 230
 231     Y' = \frac{219}{256} * (0.2126R' + 0.7152G' + 0.0722B') + \frac{16}{256}
 232
 233     Cb = \frac{224}{256} * (-0.1146R' - 0.3854G' + 0.5B')
 234
 235     Cr = \frac{224}{256} * (0.5R' - 0.4542G' - 0.0458B')
 236
 237 The xvYCC 601 encoding (``V4L2_YCBCR_ENC_XV601``, :ref:`xvycc`) is
 238 similar to the BT.601 encoding, but it allows for R', G' and B' values
 239 that are outside the range [0…1]. The resulting Y', Cb and Cr values are
 240 scaled and offset:
 241
 242 .. math::
 243
 244     Y' = \frac{219}{256} * (0.2990R' + 0.5870G' + 0.1140B') + \frac{16}{256}
 245
 246     Cb = \frac{224}{256} * (-0.1687R' - 0.3313G' + 0.5B')
 247
 248     Cr = \frac{224}{256} * (0.5R' - 0.4187G' - 0.0813B')
 249
 250 Y' is clamped to the range [0…1] and Cb and Cr are clamped to the range
 251 [-0.5…0.5]. The non-standard xvYCC 709 or xvYCC 601 encodings can be
 252 used by selecting ``V4L2_YCBCR_ENC_XV709`` or ``V4L2_YCBCR_ENC_XV601``.
 253 The xvYCC encodings always use full range quantization.
 254
 255
 256 .. _col-srgb:
 257
 258 Colorspace sRGB (V4L2_COLORSPACE_SRGB)
 259 ======================================
 260
 261 The :ref:`srgb` standard defines the colorspace used by most webcams
 262 and computer graphics. The default transfer function is
 263 ``V4L2_XFER_FUNC_SRGB``. The default Y'CbCr encoding is
 264 ``V4L2_YCBCR_ENC_601``. The default Y'CbCr quantization is full range.
 265 The chromaticities of the primary colors and the white reference are:
 266
 267
 268
 269 .. tabularcolumns:: |p{4.4cm}|p{4.4cm}|p{8.7cm}|
 270
 271 .. flat-table:: sRGB Chromaticities
 272     :header-rows:  1
 273     :stub-columns: 0
 274     :widths:       1 1 2
 275
 276
 277     -  .. row 1
 278
 279        -  Color
 280
 281        -  x
 282
 283        -  y
 284
 285     -  .. row 2
 286
 287        -  Red
 288
 289        -  0.640
 290
 291        -  0.330
 292
 293     -  .. row 3
 294
 295        -  Green
 296
 297        -  0.300
 298
 299        -  0.600
 300
 301     -  .. row 4
 302
 303        -  Blue
 304
 305        -  0.150
 306
 307        -  0.060
 308
 309     -  .. row 5
 310
 311        -  White Reference (D65)
 312
 313        -  0.3127
 314
 315        -  0.3290
 316
 317
 318 These chromaticities are identical to the Rec. 709 colorspace.
 319
 320 Transfer function. Note that negative values for L are only used by the
 321 Y'CbCr conversion.
 322
 323 .. math::
 324
 325     L' = -1.055(-L)^{\frac{1}{2.4} } + 0.055\text{, for }L < -0.0031308
 326
 327     L' = 12.92L\text{, for }-0.0031308 \le L \le 0.0031308
 328
 329     L' = 1.055L ^{\frac{1}{2.4} } - 0.055\text{, for }0.0031308 < L \le 1
 330
 331 Inverse Transfer function:
 332
 333 .. math::
 334
 335     L = -((-L' + 0.055) / 1.055) ^{2.4}\text{, for }L' < -0.04045
 336
 337     L = L' / 12.92\text{, for }-0.04045 \le L' \le 0.04045
 338
 339     L = ((L' + 0.055) / 1.055) ^{2.4}\text{, for }L' > 0.04045
 340
 341 The luminance (Y') and color difference (Cb and Cr) are obtained with
 342 the following ``V4L2_YCBCR_ENC_601`` encoding as defined by :ref:`sycc`:
 343
 344 .. math::
 345
 346     Y' = 0.2990R' + 0.5870G' + 0.1140B'
 347
 348     Cb = -0.1687R' - 0.3313G' + 0.5B'
 349
 350     Cr = 0.5R' - 0.4187G' - 0.0813B'
 351
 352 Y' is clamped to the range [0…1] and Cb and Cr are clamped to the range
 353 [-0.5…0.5]. This transform is identical to one defined in SMPTE
 354 170M/BT.601. The Y'CbCr quantization is full range.
 355
 356
 357 .. _col-adobergb:
 358
 359 Colorspace Adobe RGB (V4L2_COLORSPACE_ADOBERGB)
 360 ===============================================
 361
 362 The :ref:`adobergb` standard defines the colorspace used by computer
 363 graphics that use the AdobeRGB colorspace. This is also known as the
 364 :ref:`oprgb` standard. The default transfer function is
 365 ``V4L2_XFER_FUNC_ADOBERGB``. The default Y'CbCr encoding is
 366 ``V4L2_YCBCR_ENC_601``. The default Y'CbCr quantization is full
 367 range. The chromaticities of the primary colors and the white reference
 368 are:
 369
 370
 371
 372 .. tabularcolumns:: |p{4.4cm}|p{4.4cm}|p{8.7cm}|
 373
 374 .. flat-table:: Adobe RGB Chromaticities
 375     :header-rows:  1
 376     :stub-columns: 0
 377     :widths:       1 1 2
 378
 379
 380     -  .. row 1
 381
 382        -  Color
 383
 384        -  x
 385
 386        -  y
 387
 388     -  .. row 2
 389
 390        -  Red
 391
 392        -  0.6400
 393
 394        -  0.3300
 395
 396     -  .. row 3
 397
 398        -  Green
 399
 400        -  0.2100
 401
 402        -  0.7100
 403
 404     -  .. row 4
 405
 406        -  Blue
 407
 408        -  0.1500
 409
 410        -  0.0600
 411
 412     -  .. row 5
 413
 414        -  White Reference (D65)
 415
 416        -  0.3127
 417
 418        -  0.3290
 419
 420
 421
 422 Transfer function:
 423
 424 .. math::
 425
 426     L' = L ^{\frac{1}{2.19921875}}
 427
 428 Inverse Transfer function:
 429
 430 .. math::
 431
 432     L = L'^{(2.19921875)}
 433
 434 The luminance (Y') and color difference (Cb and Cr) are obtained with
 435 the following ``V4L2_YCBCR_ENC_601`` encoding:
 436
 437 .. math::
 438
 439     Y' = 0.2990R' + 0.5870G' + 0.1140B'
 440
 441     Cb = -0.1687R' - 0.3313G' + 0.5B'
 442
 443     Cr = 0.5R' - 0.4187G' - 0.0813B'
 444
 445 Y' is clamped to the range [0…1] and Cb and Cr are clamped to the range
 446 [-0.5…0.5]. This transform is identical to one defined in SMPTE
 447 170M/BT.601. The Y'CbCr quantization is full range.
 448
 449
 450 .. _col-bt2020:
 451
 452 Colorspace BT.2020 (V4L2_COLORSPACE_BT2020)
 453 ===========================================
 454
 455 The :ref:`itu2020` standard defines the colorspace used by Ultra-high
 456 definition television (UHDTV). The default transfer function is
 457 ``V4L2_XFER_FUNC_709``. The default Y'CbCr encoding is
 458 ``V4L2_YCBCR_ENC_BT2020``. The default R'G'B' quantization is limited
 459 range (!), and so is the default Y'CbCr quantization. The chromaticities
 460 of the primary colors and the white reference are:
 461
 462
 463
 464 .. tabularcolumns:: |p{4.4cm}|p{4.4cm}|p{8.7cm}|
 465
 466 .. flat-table:: BT.2020 Chromaticities
 467     :header-rows:  1
 468     :stub-columns: 0
 469     :widths:       1 1 2
 470
 471
 472     -  .. row 1
 473
 474        -  Color
 475
 476        -  x
 477
 478        -  y
 479
 480     -  .. row 2
 481
 482        -  Red
 483
 484        -  0.708
 485
 486        -  0.292
 487
 488     -  .. row 3
 489
 490        -  Green
 491
 492        -  0.170
 493
 494        -  0.797
 495
 496     -  .. row 4
 497
 498        -  Blue
 499
 500        -  0.131
 501
 502        -  0.046
 503
 504     -  .. row 5
 505
 506        -  White Reference (D65)
 507
 508        -  0.3127
 509
 510        -  0.3290
 511
 512
 513
 514 Transfer function (same as Rec. 709):
 515
 516 .. math::
 517
 518     L' = 4.5L\text{, for }0 \le L < 0.018
 519
 520     L' = 1.099L ^{0.45} - 0.099\text{, for } 0.018 \le L \le 1
 521
 522 Inverse Transfer function:
 523
 524 .. math::
 525
 526     L = L' / 4.5\text{, for } L' < 0.081
 527
 528     L = \left( \frac{L' + 0.099}{1.099}\right) ^{\frac{1}{0.45} }\text{, for } L' \ge 0.081
 529
 530 The luminance (Y') and color difference (Cb and Cr) are obtained with
 531 the following ``V4L2_YCBCR_ENC_BT2020`` encoding:
 532
 533 .. math::
 534
 535     Y' = 0.2627R' + 0.6780G' + 0.0593B'
 536
 537     Cb = -0.1396R' - 0.3604G' + 0.5B'
 538
 539     Cr = 0.5R' - 0.4598G' - 0.0402B'
 540
 541 Y' is clamped to the range [0…1] and Cb and Cr are clamped to the range
 542 [-0.5…0.5]. The Y'CbCr quantization is limited range.
 543
 544 There is also an alternate constant luminance R'G'B' to Yc'CbcCrc
 545 (``V4L2_YCBCR_ENC_BT2020_CONST_LUM``) encoding:
 546
 547 Luma:
 548
 549 .. math::
 550     :nowrap:
 551
 552     \begin{align*}
 553     Yc' = (0.2627R + 0.6780G + 0.0593B)'& \\
 554     B' - Yc' \le 0:& \\
 555         &Cbc = (B' - Yc') / 1.9404 \\
 556     B' - Yc' > 0: & \\
 557         &Cbc = (B' - Yc') / 1.5816 \\
 558     R' - Yc' \le 0:& \\
 559         &Crc = (R' - Y') / 1.7184 \\
 560     R' - Yc' > 0:& \\
 561         &Crc = (R' - Y') / 0.9936
 562     \end{align*}
 563
 564 Yc' is clamped to the range [0…1] and Cbc and Crc are clamped to the
 565 range [-0.5…0.5]. The Yc'CbcCrc quantization is limited range.
 566
 567
 568 .. _col-dcip3:
 569
 570 Colorspace DCI-P3 (V4L2_COLORSPACE_DCI_P3)
 571 ==========================================
 572
 573 The :ref:`smpte431` standard defines the colorspace used by cinema
 574 projectors that use the DCI-P3 colorspace. The default transfer function
 575 is ``V4L2_XFER_FUNC_DCI_P3``. The default Y'CbCr encoding is
 576 ``V4L2_YCBCR_ENC_709``. The default Y'CbCr quantization is limited range.
 577
 578 .. note::
 579
 580    Note that this colorspace standard does not specify a
 581    Y'CbCr encoding since it is not meant to be encoded to Y'CbCr. So this
 582    default Y'CbCr encoding was picked because it is the HDTV encoding.
 583
 584 The chromaticities of the primary colors and the white reference are:
 585
 586
 587
 588 .. tabularcolumns:: |p{4.4cm}|p{4.4cm}|p{8.7cm}|
 589
 590 .. flat-table:: DCI-P3 Chromaticities
 591     :header-rows:  1
 592     :stub-columns: 0
 593     :widths:       1 1 2
 594
 595
 596     -  .. row 1
 597
 598        -  Color
 599
 600        -  x
 601
 602        -  y
 603
 604     -  .. row 2
 605
 606        -  Red
 607
 608        -  0.6800
 609
 610        -  0.3200
 611
 612     -  .. row 3
 613
 614        -  Green
 615
 616        -  0.2650
 617
 618        -  0.6900
 619
 620     -  .. row 4
 621
 622        -  Blue
 623
 624        -  0.1500
 625
 626        -  0.0600
 627
 628     -  .. row 5
 629
 630        -  White Reference
 631
 632        -  0.3140
 633
 634        -  0.3510
 635
 636
 637
 638 Transfer function:
 639
 640 .. math::
 641
 642     L' = L^{\frac{1}{2.6}}
 643
 644 Inverse Transfer function:
 645
 646 .. math::
 647
 648     L = L'^{(2.6)}
 649
 650 Y'CbCr encoding is not specified. V4L2 defaults to Rec. 709.
 651
 652
 653 .. _col-smpte-240m:
 654
 655 Colorspace SMPTE 240M (V4L2_COLORSPACE_SMPTE240M)
 656 =================================================
 657
 658 The :ref:`smpte240m` standard was an interim standard used during the
 659 early days of HDTV (1988-1998). It has been superseded by Rec. 709. The
 660 default transfer function is ``V4L2_XFER_FUNC_SMPTE240M``. The default
 661 Y'CbCr encoding is ``V4L2_YCBCR_ENC_SMPTE240M``. The default Y'CbCr
 662 quantization is limited range. The chromaticities of the primary colors
 663 and the white reference are:
 664
 665
 666
 667 .. tabularcolumns:: |p{4.4cm}|p{4.4cm}|p{8.7cm}|
 668
 669 .. flat-table:: SMPTE 240M Chromaticities
 670     :header-rows:  1
 671     :stub-columns: 0
 672     :widths:       1 1 2
 673
 674
 675     -  .. row 1
 676
 677        -  Color
 678
 679        -  x
 680
 681        -  y
 682
 683     -  .. row 2
 684
 685        -  Red
 686
 687        -  0.630
 688
 689        -  0.340
 690
 691     -  .. row 3
 692
 693        -  Green
 694
 695        -  0.310
 696
 697        -  0.595
 698
 699     -  .. row 4
 700
 701        -  Blue
 702
 703        -  0.155
 704
 705        -  0.070
 706
 707     -  .. row 5
 708
 709        -  White Reference (D65)
 710
 711        -  0.3127
 712
 713        -  0.3290
 714
 715
 716 These chromaticities are identical to the SMPTE 170M colorspace.
 717
 718 Transfer function:
 719
 720 .. math::
 721
 722     L' = 4L\text{, for } 0 \le L < 0.0228
 723
 724     L' = 1.1115L ^{0.45} - 0.1115\text{, for } 0.0228 \le L \le 1
 725
 726 Inverse Transfer function:
 727
 728 .. math::
 729
 730     L = \frac{L'}{4}\text{, for } 0 \le L' < 0.0913
 731
 732     L = \left( \frac{L' + 0.1115}{1.1115}\right) ^{\frac{1}{0.45} }\text{, for } L' \ge 0.0913
 733
 734 The luminance (Y') and color difference (Cb and Cr) are obtained with
 735 the following ``V4L2_YCBCR_ENC_SMPTE240M`` encoding:
 736
 737 .. math::
 738
 739     Y' = 0.2122R' + 0.7013G' + 0.0865B'
 740
 741     Cb = -0.1161R' - 0.3839G' + 0.5B'
 742
 743     Cr = 0.5R' - 0.4451G' - 0.0549B'
 744
 745 Y' is clamped to the range [0…1] and Cb and Cr are clamped to the
 746 range [-0.5…0.5]. The Y'CbCr quantization is limited range.
 747
 748
 749 .. _col-sysm:
 750
 751 Colorspace NTSC 1953 (V4L2_COLORSPACE_470_SYSTEM_M)
 752 ===================================================
 753
 754 This standard defines the colorspace used by NTSC in 1953. In practice
 755 this colorspace is obsolete and SMPTE 170M should be used instead. The
 756 default transfer function is ``V4L2_XFER_FUNC_709``. The default Y'CbCr
 757 encoding is ``V4L2_YCBCR_ENC_601``. The default Y'CbCr quantization is
 758 limited range. The chromaticities of the primary colors and the white
 759 reference are:
 760
 761
 762
 763 .. tabularcolumns:: |p{4.4cm}|p{4.4cm}|p{8.7cm}|
 764
 765 .. flat-table:: NTSC 1953 Chromaticities
 766     :header-rows:  1
 767     :stub-columns: 0
 768     :widths:       1 1 2
 769
 770
 771     -  .. row 1
 772
 773        -  Color
 774
 775        -  x
 776
 777        -  y
 778
 779     -  .. row 2
 780
 781        -  Red
 782
 783        -  0.67
 784
 785        -  0.33
 786
 787     -  .. row 3
 788
 789        -  Green
 790
 791        -  0.21
 792
 793        -  0.71
 794
 795     -  .. row 4
 796
 797        -  Blue
 798
 799        -  0.14
 800
 801        -  0.08
 802
 803     -  .. row 5
 804
 805        -  White Reference (C)
 806
 807        -  0.310
 808
 809        -  0.316
 810
 811
 812 .. note::
 813
 814    This colorspace uses Illuminant C instead of D65 as the white
 815    reference. To correctly convert an image in this colorspace to another
 816    that uses D65 you need to apply a chromatic adaptation algorithm such as
 817    the Bradford method.
 818
 819 The transfer function was never properly defined for NTSC 1953. The Rec.
 820 709 transfer function is recommended in the literature:
 821
 822 .. math::
 823
 824     L' = 4.5L\text{, for } 0 \le L < 0.018
 825
 826     L' = 1.099L ^{0.45} - 0.099\text{, for } 0.018 \le L \le 1
 827
 828 Inverse Transfer function:
 829
 830 .. math::
 831
 832     L = \frac{L'}{4.5} \text{, for } L' < 0.081
 833
 834     L = \left( \frac{L' + 0.099}{1.099}\right) ^{\frac{1}{0.45} }\text{, for } L' \ge 0.081
 835
 836 The luminance (Y') and color difference (Cb and Cr) are obtained with
 837 the following ``V4L2_YCBCR_ENC_601`` encoding:
 838
 839 .. math::
 840
 841     Y' = 0.2990R' + 0.5870G' + 0.1140B'
 842
 843     Cb = -0.1687R' - 0.3313G' + 0.5B'
 844
 845     Cr = 0.5R' - 0.4187G' - 0.0813B'
 846
 847 Y' is clamped to the range [0…1] and Cb and Cr are clamped to the range
 848 [-0.5…0.5]. The Y'CbCr quantization is limited range. This transform is
 849 identical to one defined in SMPTE 170M/BT.601.
 850
 851
 852 .. _col-sysbg:
 853
 854 Colorspace EBU Tech. 3213 (V4L2_COLORSPACE_470_SYSTEM_BG)
 855 =========================================================
 856
 857 The :ref:`tech3213` standard defines the colorspace used by PAL/SECAM
 858 in 1975. In practice this colorspace is obsolete and SMPTE 170M should
 859 be used instead. The default transfer function is
 860 ``V4L2_XFER_FUNC_709``. The default Y'CbCr encoding is
 861 ``V4L2_YCBCR_ENC_601``. The default Y'CbCr quantization is limited
 862 range. The chromaticities of the primary colors and the white reference
 863 are:
 864
 865
 866
 867 .. tabularcolumns:: |p{4.4cm}|p{4.4cm}|p{8.7cm}|
 868
 869 .. flat-table:: EBU Tech. 3213 Chromaticities
 870     :header-rows:  1
 871     :stub-columns: 0
 872     :widths:       1 1 2
 873
 874
 875     -  .. row 1
 876
 877        -  Color
 878
 879        -  x
 880
 881        -  y
 882
 883     -  .. row 2
 884
 885        -  Red
 886
 887        -  0.64
 888
 889        -  0.33
 890
 891     -  .. row 3
 892
 893        -  Green
 894
 895        -  0.29
 896
 897        -  0.60
 898
 899     -  .. row 4
 900
 901        -  Blue
 902
 903        -  0.15
 904
 905        -  0.06
 906
 907     -  .. row 5
 908
 909        -  White Reference (D65)
 910
 911        -  0.3127
 912
 913        -  0.3290
 914
 915
 916
 917 The transfer function was never properly defined for this colorspace.
 918 The Rec. 709 transfer function is recommended in the literature:
 919
 920 .. math::
 921
 922     L' = 4.5L\text{, for } 0 \le L < 0.018
 923
 924     L' = 1.099L ^{0.45} - 0.099\text{, for } 0.018 \le L \le 1
 925
 926 Inverse Transfer function:
 927
 928 .. math::
 929
 930     L = \frac{L'}{4.5} \text{, for } L' < 0.081
 931
 932     L = \left(\frac{L' + 0.099}{1.099} \right) ^{\frac{1}{0.45} }\text{, for } L' \ge 0.081
 933
 934 The luminance (Y') and color difference (Cb and Cr) are obtained with
 935 the following ``V4L2_YCBCR_ENC_601`` encoding:
 936
 937 .. math::
 938
 939     Y' = 0.2990R' + 0.5870G' + 0.1140B'
 940
 941     Cb = -0.1687R' - 0.3313G' + 0.5B'
 942
 943     Cr = 0.5R' - 0.4187G' - 0.0813B'
 944
 945 Y' is clamped to the range [0…1] and Cb and Cr are clamped to the range
 946 [-0.5…0.5]. The Y'CbCr quantization is limited range. This transform is
 947 identical to one defined in SMPTE 170M/BT.601.
 948
 949
 950 .. _col-jpeg:
 951
 952 Colorspace JPEG (V4L2_COLORSPACE_JPEG)
 953 ======================================
 954
 955 This colorspace defines the colorspace used by most (Motion-)JPEG
 956 formats. The chromaticities of the primary colors and the white
 957 reference are identical to sRGB. The transfer function use is
 958 ``V4L2_XFER_FUNC_SRGB``. The Y'CbCr encoding is ``V4L2_YCBCR_ENC_601``
 959 with full range quantization where Y' is scaled to [0…255] and Cb/Cr are
 960 scaled to [-128…128] and then clipped to [-128…127].
 961
 962 .. note::
 963
 964    The JPEG standard does not actually store colorspace
 965    information. So if something other than sRGB is used, then the driver
 966    will have to set that information explicitly. Effectively
 967    ``V4L2_COLORSPACE_JPEG`` can be considered to be an abbreviation for
 968    ``V4L2_COLORSPACE_SRGB``, ``V4L2_YCBCR_ENC_601`` and
 969    ``V4L2_QUANTIZATION_FULL_RANGE``.