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 .. flat-table:: SMPTE 170M Chromaticities
  23     :header-rows:  1
  24     :stub-columns: 0
  25     :widths:       1 1 2
  26
  27
  28     -  .. row 1
  29
  30        -  Color
  31
  32        -  x
  33
  34        -  y
  35
  36     -  .. row 2
  37
  38        -  Red
  39
  40        -  0.630
  41
  42        -  0.340
  43
  44     -  .. row 3
  45
  46        -  Green
  47
  48        -  0.310
  49
  50        -  0.595
  51
  52     -  .. row 4
  53
  54        -  Blue
  55
  56        -  0.155
  57
  58        -  0.070
  59
  60     -  .. row 5
  61
  62        -  White Reference (D65)
  63
  64        -  0.3127
  65
  66        -  0.3290
  67
  68
  69 The red, green and blue chromaticities are also often referred to as the
  70 SMPTE C set, so this colorspace is sometimes called SMPTE C as well.
  71
  72 The transfer function defined for SMPTE 170M is the same as the one
  73 defined in Rec. 709.
  74
  75     L' = -1.099(-L) :sup:`0.45` + 0.099 for L ≤ -0.018
  76
  77     L' = 4.5L for -0.018 < L < 0.018
  78
  79     L' = 1.099L :sup:`0.45` - 0.099 for L ≥ 0.018
  80
  81 Inverse Transfer function:
  82
  83     L = -((L' - 0.099) / -1.099) :sup:`1/0.45` for L' ≤ -0.081
  84
  85     L = L' / 4.5 for -0.081 < L' < 0.081
  86
  87     L = ((L' + 0.099) / 1.099) :sup:`1/0.45` for L' ≥ 0.081
  88
  89 The luminance (Y') and color difference (Cb and Cr) are obtained with
  90 the following ``V4L2_YCBCR_ENC_601`` encoding:
  91
  92     Y' = 0.299R' + 0.587G' + 0.114B'
  93
  94     Cb = -0.169R' - 0.331G' + 0.5B'
  95
  96     Cr = 0.5R' - 0.419G' - 0.081B'
  97
  98 Y' is clamped to the range [0…1] and Cb and Cr are clamped to the range
  99 [-0.5…0.5]. This conversion to Y'CbCr is identical to the one defined in
 100 the :ref:`itu601` standard and this colorspace is sometimes called
 101 BT.601 as well, even though BT.601 does not mention any color primaries.
 102
 103 The default quantization is limited range, but full range is possible
 104 although rarely seen.
 105
 106
 107 .. _col-rec709:
 108
 109 Colorspace Rec. 709 (V4L2_COLORSPACE_REC709)
 110 ============================================
 111
 112 The :ref:`itu709` standard defines the colorspace used by HDTV in
 113 general. The default transfer function is ``V4L2_XFER_FUNC_709``. The
 114 default Y'CbCr encoding is ``V4L2_YCBCR_ENC_709``. The default Y'CbCr
 115 quantization is limited range. The chromaticities of the primary colors
 116 and the white reference are:
 117
 118
 119
 120 .. flat-table:: Rec. 709 Chromaticities
 121     :header-rows:  1
 122     :stub-columns: 0
 123     :widths:       1 1 2
 124
 125
 126     -  .. row 1
 127
 128        -  Color
 129
 130        -  x
 131
 132        -  y
 133
 134     -  .. row 2
 135
 136        -  Red
 137
 138        -  0.640
 139
 140        -  0.330
 141
 142     -  .. row 3
 143
 144        -  Green
 145
 146        -  0.300
 147
 148        -  0.600
 149
 150     -  .. row 4
 151
 152        -  Blue
 153
 154        -  0.150
 155
 156        -  0.060
 157
 158     -  .. row 5
 159
 160        -  White Reference (D65)
 161
 162        -  0.3127
 163
 164        -  0.3290
 165
 166
 167 The full name of this standard is Rec. ITU-R BT.709-5.
 168
 169 Transfer function. Normally L is in the range [0…1], but for the
 170 extended gamut xvYCC encoding values outside that range are allowed.
 171
 172     L' = -1.099(-L) :sup:`0.45` + 0.099 for L ≤ -0.018
 173
 174     L' = 4.5L for -0.018 < L < 0.018
 175
 176     L' = 1.099L :sup:`0.45` - 0.099 for L ≥ 0.018
 177
 178 Inverse Transfer function:
 179
 180     L = -((L' - 0.099) / -1.099) :sup:`1/0.45` for L' ≤ -0.081
 181
 182     L = L' / 4.5 for -0.081 < L' < 0.081
 183
 184     L = ((L' + 0.099) / 1.099) :sup:`1/0.45` for L' ≥ 0.081
 185
 186 The luminance (Y') and color difference (Cb and Cr) are obtained with
 187 the following ``V4L2_YCBCR_ENC_709`` encoding:
 188
 189     Y' = 0.2126R' + 0.7152G' + 0.0722B'
 190
 191     Cb = -0.1146R' - 0.3854G' + 0.5B'
 192
 193     Cr = 0.5R' - 0.4542G' - 0.0458B'
 194
 195 Y' is clamped to the range [0…1] and Cb and Cr are clamped to the range
 196 [-0.5…0.5].
 197
 198 The default quantization is limited range, but full range is possible
 199 although rarely seen.
 200
 201 The ``V4L2_YCBCR_ENC_709`` encoding described above is the default for
 202 this colorspace, but it can be overridden with ``V4L2_YCBCR_ENC_601``,
 203 in which case the BT.601 Y'CbCr encoding is used.
 204
 205 Two additional extended gamut Y'CbCr encodings are also possible with
 206 this colorspace:
 207
 208 The xvYCC 709 encoding (``V4L2_YCBCR_ENC_XV709``, :ref:`xvycc`) is
 209 similar to the Rec. 709 encoding, but it allows for R', G' and B' values
 210 that are outside the range [0…1]. The resulting Y', Cb and Cr values are
 211 scaled and offset:
 212
 213     Y' = (219 / 256) * (0.2126R' + 0.7152G' + 0.0722B') + (16 / 256)
 214
 215     Cb = (224 / 256) * (-0.1146R' - 0.3854G' + 0.5B')
 216
 217     Cr = (224 / 256) * (0.5R' - 0.4542G' - 0.0458B')
 218
 219 The xvYCC 601 encoding (``V4L2_YCBCR_ENC_XV601``, :ref:`xvycc`) is
 220 similar to the BT.601 encoding, but it allows for R', G' and B' values
 221 that are outside the range [0…1]. The resulting Y', Cb and Cr values are
 222 scaled and offset:
 223
 224     Y' = (219 / 256) * (0.299R' + 0.587G' + 0.114B') + (16 / 256)
 225
 226     Cb = (224 / 256) * (-0.169R' - 0.331G' + 0.5B')
 227
 228     Cr = (224 / 256) * (0.5R' - 0.419G' - 0.081B')
 229
 230 Y' is clamped to the range [0…1] and Cb and Cr are clamped to the range
 231 [-0.5…0.5]. The non-standard xvYCC 709 or xvYCC 601 encodings can be
 232 used by selecting ``V4L2_YCBCR_ENC_XV709`` or ``V4L2_YCBCR_ENC_XV601``.
 233 The xvYCC encodings always use full range quantization.
 234
 235
 236 .. _col-srgb:
 237
 238 Colorspace sRGB (V4L2_COLORSPACE_SRGB)
 239 ======================================
 240
 241 The :ref:`srgb` standard defines the colorspace used by most webcams
 242 and computer graphics. The default transfer function is
 243 ``V4L2_XFER_FUNC_SRGB``. The default Y'CbCr encoding is
 244 ``V4L2_YCBCR_ENC_SYCC``. The default Y'CbCr quantization is full range.
 245 The chromaticities of the primary colors and the white reference are:
 246
 247
 248
 249 .. flat-table:: sRGB Chromaticities
 250     :header-rows:  1
 251     :stub-columns: 0
 252     :widths:       1 1 2
 253
 254
 255     -  .. row 1
 256
 257        -  Color
 258
 259        -  x
 260
 261        -  y
 262
 263     -  .. row 2
 264
 265        -  Red
 266
 267        -  0.640
 268
 269        -  0.330
 270
 271     -  .. row 3
 272
 273        -  Green
 274
 275        -  0.300
 276
 277        -  0.600
 278
 279     -  .. row 4
 280
 281        -  Blue
 282
 283        -  0.150
 284
 285        -  0.060
 286
 287     -  .. row 5
 288
 289        -  White Reference (D65)
 290
 291        -  0.3127
 292
 293        -  0.3290
 294
 295
 296 These chromaticities are identical to the Rec. 709 colorspace.
 297
 298 Transfer function. Note that negative values for L are only used by the
 299 Y'CbCr conversion.
 300
 301     L' = -1.055(-L) :sup:`1/2.4` + 0.055 for L < -0.0031308
 302
 303     L' = 12.92L for -0.0031308 ≤ L ≤ 0.0031308
 304
 305     L' = 1.055L :sup:`1/2.4` - 0.055 for 0.0031308 < L ≤ 1
 306
 307 Inverse Transfer function:
 308
 309     L = -((-L' + 0.055) / 1.055) :sup:`2.4` for L' < -0.04045
 310
 311     L = L' / 12.92 for -0.04045 ≤ L' ≤ 0.04045
 312
 313     L = ((L' + 0.055) / 1.055) :sup:`2.4` for L' > 0.04045
 314
 315 The luminance (Y') and color difference (Cb and Cr) are obtained with
 316 the following ``V4L2_YCBCR_ENC_SYCC`` encoding as defined by
 317 :ref:`sycc`:
 318
 319     Y' = 0.2990R' + 0.5870G' + 0.1140B'
 320
 321     Cb = -0.1687R' - 0.3313G' + 0.5B'
 322
 323     Cr = 0.5R' - 0.4187G' - 0.0813B'
 324
 325 Y' is clamped to the range [0…1] and Cb and Cr are clamped to the range
 326 [-0.5…0.5]. The ``V4L2_YCBCR_ENC_SYCC`` quantization is always full
 327 range. Although this Y'CbCr encoding looks very similar to the
 328 ``V4L2_YCBCR_ENC_XV601`` encoding, it is not. The
 329 ``V4L2_YCBCR_ENC_XV601`` scales and offsets the Y'CbCr values before
 330 quantization, but this encoding does not do that.
 331
 332
 333 .. _col-adobergb:
 334
 335 Colorspace Adobe RGB (V4L2_COLORSPACE_ADOBERGB)
 336 ===============================================
 337
 338 The :ref:`adobergb` standard defines the colorspace used by computer
 339 graphics that use the AdobeRGB colorspace. This is also known as the
 340 :ref:`oprgb` standard. The default transfer function is
 341 ``V4L2_XFER_FUNC_ADOBERGB``. The default Y'CbCr encoding is
 342 ``V4L2_YCBCR_ENC_601``. The default Y'CbCr quantization is limited
 343 range. The chromaticities of the primary colors and the white reference
 344 are:
 345
 346
 347
 348 .. flat-table:: Adobe RGB Chromaticities
 349     :header-rows:  1
 350     :stub-columns: 0
 351     :widths:       1 1 2
 352
 353
 354     -  .. row 1
 355
 356        -  Color
 357
 358        -  x
 359
 360        -  y
 361
 362     -  .. row 2
 363
 364        -  Red
 365
 366        -  0.6400
 367
 368        -  0.3300
 369
 370     -  .. row 3
 371
 372        -  Green
 373
 374        -  0.2100
 375
 376        -  0.7100
 377
 378     -  .. row 4
 379
 380        -  Blue
 381
 382        -  0.1500
 383
 384        -  0.0600
 385
 386     -  .. row 5
 387
 388        -  White Reference (D65)
 389
 390        -  0.3127
 391
 392        -  0.3290
 393
 394
 395
 396 Transfer function:
 397
 398     L' = L :sup:`1/2.19921875`
 399
 400 Inverse Transfer function:
 401
 402     L = L' :sup:`2.19921875`
 403
 404 The luminance (Y') and color difference (Cb and Cr) are obtained with
 405 the following ``V4L2_YCBCR_ENC_601`` encoding:
 406
 407     Y' = 0.299R' + 0.587G' + 0.114B'
 408
 409     Cb = -0.169R' - 0.331G' + 0.5B'
 410
 411     Cr = 0.5R' - 0.419G' - 0.081B'
 412
 413 Y' is clamped to the range [0…1] and Cb and Cr are clamped to the range
 414 [-0.5…0.5]. This transform is identical to one defined in SMPTE
 415 170M/BT.601. The Y'CbCr quantization is limited range.
 416
 417
 418 .. _col-bt2020:
 419
 420 Colorspace BT.2020 (V4L2_COLORSPACE_BT2020)
 421 ===========================================
 422
 423 The :ref:`itu2020` standard defines the colorspace used by Ultra-high
 424 definition television (UHDTV). The default transfer function is
 425 ``V4L2_XFER_FUNC_709``. The default Y'CbCr encoding is
 426 ``V4L2_YCBCR_ENC_BT2020``. The default R'G'B' quantization is limited
 427 range (!), and so is the default Y'CbCr quantization. The chromaticities
 428 of the primary colors and the white reference are:
 429
 430
 431
 432 .. flat-table:: BT.2020 Chromaticities
 433     :header-rows:  1
 434     :stub-columns: 0
 435     :widths:       1 1 2
 436
 437
 438     -  .. row 1
 439
 440        -  Color
 441
 442        -  x
 443
 444        -  y
 445
 446     -  .. row 2
 447
 448        -  Red
 449
 450        -  0.708
 451
 452        -  0.292
 453
 454     -  .. row 3
 455
 456        -  Green
 457
 458        -  0.170
 459
 460        -  0.797
 461
 462     -  .. row 4
 463
 464        -  Blue
 465
 466        -  0.131
 467
 468        -  0.046
 469
 470     -  .. row 5
 471
 472        -  White Reference (D65)
 473
 474        -  0.3127
 475
 476        -  0.3290
 477
 478
 479
 480 Transfer function (same as Rec. 709):
 481
 482     L' = 4.5L for 0 ≤ L < 0.018
 483
 484     L' = 1.099L :sup:`0.45` - 0.099 for 0.018 ≤ L ≤ 1
 485
 486 Inverse Transfer function:
 487
 488     L = L' / 4.5 for L' < 0.081
 489
 490     L = ((L' + 0.099) / 1.099) :sup:`1/0.45` for L' ≥ 0.081
 491
 492 The luminance (Y') and color difference (Cb and Cr) are obtained with
 493 the following ``V4L2_YCBCR_ENC_BT2020`` encoding:
 494
 495     Y' = 0.2627R' + 0.6780G' + 0.0593B'
 496
 497     Cb = -0.1396R' - 0.3604G' + 0.5B'
 498
 499     Cr = 0.5R' - 0.4598G' - 0.0402B'
 500
 501 Y' is clamped to the range [0…1] and Cb and Cr are clamped to the range
 502 [-0.5…0.5]. The Y'CbCr quantization is limited range.
 503
 504 There is also an alternate constant luminance R'G'B' to Yc'CbcCrc
 505 (``V4L2_YCBCR_ENC_BT2020_CONST_LUM``) encoding:
 506
 507 Luma:
 508
 509     Yc' = (0.2627R + 0.6780G + 0.0593B)'
 510
 511 B' - Yc' ≤ 0:
 512
 513     Cbc = (B' - Yc') / 1.9404
 514
 515 B' - Yc' > 0:
 516
 517     Cbc = (B' - Yc') / 1.5816
 518
 519 R' - Yc' ≤ 0:
 520
 521     Crc = (R' - Y') / 1.7184
 522
 523 R' - Yc' > 0:
 524
 525     Crc = (R' - Y') / 0.9936
 526
 527 Yc' is clamped to the range [0…1] and Cbc and Crc are clamped to the
 528 range [-0.5…0.5]. The Yc'CbcCrc quantization is limited range.
 529
 530
 531 .. _col-dcip3:
 532
 533 Colorspace DCI-P3 (V4L2_COLORSPACE_DCI_P3)
 534 ==========================================
 535
 536 The :ref:`smpte431` standard defines the colorspace used by cinema
 537 projectors that use the DCI-P3 colorspace. The default transfer function
 538 is ``V4L2_XFER_FUNC_DCI_P3``. The default Y'CbCr encoding is
 539 ``V4L2_YCBCR_ENC_709``. Note that this colorspace does not specify a
 540 Y'CbCr encoding since it is not meant to be encoded to Y'CbCr. So this
 541 default Y'CbCr encoding was picked because it is the HDTV encoding. The
 542 default Y'CbCr quantization is limited range. The chromaticities of the
 543 primary colors and the white reference are:
 544
 545
 546
 547 .. flat-table:: DCI-P3 Chromaticities
 548     :header-rows:  1
 549     :stub-columns: 0
 550     :widths:       1 1 2
 551
 552
 553     -  .. row 1
 554
 555        -  Color
 556
 557        -  x
 558
 559        -  y
 560
 561     -  .. row 2
 562
 563        -  Red
 564
 565        -  0.6800
 566
 567        -  0.3200
 568
 569     -  .. row 3
 570
 571        -  Green
 572
 573        -  0.2650
 574
 575        -  0.6900
 576
 577     -  .. row 4
 578
 579        -  Blue
 580
 581        -  0.1500
 582
 583        -  0.0600
 584
 585     -  .. row 5
 586
 587        -  White Reference
 588
 589        -  0.3140
 590
 591        -  0.3510
 592
 593
 594
 595 Transfer function:
 596
 597     L' = L :sup:`1/2.6`
 598
 599 Inverse Transfer function:
 600
 601     L = L' :sup:`2.6`
 602
 603 Y'CbCr encoding is not specified. V4L2 defaults to Rec. 709.
 604
 605
 606 .. _col-smpte-240m:
 607
 608 Colorspace SMPTE 240M (V4L2_COLORSPACE_SMPTE240M)
 609 =================================================
 610
 611 The :ref:`smpte240m` standard was an interim standard used during the
 612 early days of HDTV (1988-1998). It has been superseded by Rec. 709. The
 613 default transfer function is ``V4L2_XFER_FUNC_SMPTE240M``. The default
 614 Y'CbCr encoding is ``V4L2_YCBCR_ENC_SMPTE240M``. The default Y'CbCr
 615 quantization is limited range. The chromaticities of the primary colors
 616 and the white reference are:
 617
 618
 619
 620 .. flat-table:: SMPTE 240M Chromaticities
 621     :header-rows:  1
 622     :stub-columns: 0
 623     :widths:       1 1 2
 624
 625
 626     -  .. row 1
 627
 628        -  Color
 629
 630        -  x
 631
 632        -  y
 633
 634     -  .. row 2
 635
 636        -  Red
 637
 638        -  0.630
 639
 640        -  0.340
 641
 642     -  .. row 3
 643
 644        -  Green
 645
 646        -  0.310
 647
 648        -  0.595
 649
 650     -  .. row 4
 651
 652        -  Blue
 653
 654        -  0.155
 655
 656        -  0.070
 657
 658     -  .. row 5
 659
 660        -  White Reference (D65)
 661
 662        -  0.3127
 663
 664        -  0.3290
 665
 666
 667 These chromaticities are identical to the SMPTE 170M colorspace.
 668
 669 Transfer function:
 670
 671     L' = 4L for 0 ≤ L < 0.0228
 672
 673     L' = 1.1115L :sup:`0.45` - 0.1115 for 0.0228 ≤ L ≤ 1
 674
 675 Inverse Transfer function:
 676
 677     L = L' / 4 for 0 ≤ L' < 0.0913
 678
 679     L = ((L' + 0.1115) / 1.1115) :sup:`1/0.45` for L' ≥ 0.0913
 680
 681 The luminance (Y') and color difference (Cb and Cr) are obtained with
 682 the following ``V4L2_YCBCR_ENC_SMPTE240M`` encoding:
 683
 684     Y' = 0.2122R' + 0.7013G' + 0.0865B'
 685
 686     Cb = -0.1161R' - 0.3839G' + 0.5B'
 687
 688     Cr = 0.5R' - 0.4451G' - 0.0549B'
 689
 690 Yc' is clamped to the range [0…1] and Cbc and Crc are clamped to the
 691 range [-0.5…0.5]. The Y'CbCr quantization is limited range.
 692
 693
 694 .. _col-sysm:
 695
 696 Colorspace NTSC 1953 (V4L2_COLORSPACE_470_SYSTEM_M)
 697 ===================================================
 698
 699 This standard defines the colorspace used by NTSC in 1953. In practice
 700 this colorspace is obsolete and SMPTE 170M should be used instead. The
 701 default transfer function is ``V4L2_XFER_FUNC_709``. The default Y'CbCr
 702 encoding is ``V4L2_YCBCR_ENC_601``. The default Y'CbCr quantization is
 703 limited range. The chromaticities of the primary colors and the white
 704 reference are:
 705
 706
 707
 708 .. flat-table:: NTSC 1953 Chromaticities
 709     :header-rows:  1
 710     :stub-columns: 0
 711     :widths:       1 1 2
 712
 713
 714     -  .. row 1
 715
 716        -  Color
 717
 718        -  x
 719
 720        -  y
 721
 722     -  .. row 2
 723
 724        -  Red
 725
 726        -  0.67
 727
 728        -  0.33
 729
 730     -  .. row 3
 731
 732        -  Green
 733
 734        -  0.21
 735
 736        -  0.71
 737
 738     -  .. row 4
 739
 740        -  Blue
 741
 742        -  0.14
 743
 744        -  0.08
 745
 746     -  .. row 5
 747
 748        -  White Reference (C)
 749
 750        -  0.310
 751
 752        -  0.316
 753
 754
 755 Note that this colorspace uses Illuminant C instead of D65 as the white
 756 reference. To correctly convert an image in this colorspace to another
 757 that uses D65 you need to apply a chromatic adaptation algorithm such as
 758 the Bradford method.
 759
 760 The transfer function was never properly defined for NTSC 1953. The Rec.
 761 709 transfer function is recommended in the literature:
 762
 763     L' = 4.5L for 0 ≤ L < 0.018
 764
 765     L' = 1.099L :sup:`0.45` - 0.099 for 0.018 ≤ L ≤ 1
 766
 767 Inverse Transfer function:
 768
 769     L = L' / 4.5 for L' < 0.081
 770
 771     L = ((L' + 0.099) / 1.099) :sup:`1/0.45` for L' ≥ 0.081
 772
 773 The luminance (Y') and color difference (Cb and Cr) are obtained with
 774 the following ``V4L2_YCBCR_ENC_601`` encoding:
 775
 776     Y' = 0.299R' + 0.587G' + 0.114B'
 777
 778     Cb = -0.169R' - 0.331G' + 0.5B'
 779
 780     Cr = 0.5R' - 0.419G' - 0.081B'
 781
 782 Y' is clamped to the range [0…1] and Cb and Cr are clamped to the range
 783 [-0.5…0.5]. The Y'CbCr quantization is limited range. This transform is
 784 identical to one defined in SMPTE 170M/BT.601.
 785
 786
 787 .. _col-sysbg:
 788
 789 Colorspace EBU Tech. 3213 (V4L2_COLORSPACE_470_SYSTEM_BG)
 790 =========================================================
 791
 792 The :ref:`tech3213` standard defines the colorspace used by PAL/SECAM
 793 in 1975. In practice this colorspace is obsolete and SMPTE 170M should
 794 be used instead. The default transfer function is
 795 ``V4L2_XFER_FUNC_709``. The default Y'CbCr encoding is
 796 ``V4L2_YCBCR_ENC_601``. The default Y'CbCr quantization is limited
 797 range. The chromaticities of the primary colors and the white reference
 798 are:
 799
 800
 801
 802 .. flat-table:: EBU Tech. 3213 Chromaticities
 803     :header-rows:  1
 804     :stub-columns: 0
 805     :widths:       1 1 2
 806
 807
 808     -  .. row 1
 809
 810        -  Color
 811
 812        -  x
 813
 814        -  y
 815
 816     -  .. row 2
 817
 818        -  Red
 819
 820        -  0.64
 821
 822        -  0.33
 823
 824     -  .. row 3
 825
 826        -  Green
 827
 828        -  0.29
 829
 830        -  0.60
 831
 832     -  .. row 4
 833
 834        -  Blue
 835
 836        -  0.15
 837
 838        -  0.06
 839
 840     -  .. row 5
 841
 842        -  White Reference (D65)
 843
 844        -  0.3127
 845
 846        -  0.3290
 847
 848
 849
 850 The transfer function was never properly defined for this colorspace.
 851 The Rec. 709 transfer function is recommended in the literature:
 852
 853     L' = 4.5L for 0 ≤ L < 0.018
 854
 855     L' = 1.099L :sup:`0.45` - 0.099 for 0.018 ≤ L ≤ 1
 856
 857 Inverse Transfer function:
 858
 859     L = L' / 4.5 for L' < 0.081
 860
 861     L = ((L' + 0.099) / 1.099) :sup:`1/0.45` for L' ≥ 0.081
 862
 863 The luminance (Y') and color difference (Cb and Cr) are obtained with
 864 the following ``V4L2_YCBCR_ENC_601`` encoding:
 865
 866     Y' = 0.299R' + 0.587G' + 0.114B'
 867
 868     Cb = -0.169R' - 0.331G' + 0.5B'
 869
 870     Cr = 0.5R' - 0.419G' - 0.081B'
 871
 872 Y' is clamped to the range [0…1] and Cb and Cr are clamped to the range
 873 [-0.5…0.5]. The Y'CbCr quantization is limited range. This transform is
 874 identical to one defined in SMPTE 170M/BT.601.
 875
 876
 877 .. _col-jpeg:
 878
 879 Colorspace JPEG (V4L2_COLORSPACE_JPEG)
 880 ======================================
 881
 882 This colorspace defines the colorspace used by most (Motion-)JPEG
 883 formats. The chromaticities of the primary colors and the white
 884 reference are identical to sRGB. The transfer function use is
 885 ``V4L2_XFER_FUNC_SRGB``. The Y'CbCr encoding is ``V4L2_YCBCR_ENC_601``
 886 with full range quantization where Y' is scaled to [0…255] and Cb/Cr are
 887 scaled to [-128…128] and then clipped to [-128…127].
 888
 889 Note that the JPEG standard does not actually store colorspace
 890 information. So if something other than sRGB is used, then the driver
 891 will have to set that information explicitly. Effectively
 892 ``V4L2_COLORSPACE_JPEG`` can be considered to be an abbreviation for
 893 ``V4L2_COLORSPACE_SRGB``, ``V4L2_YCBCR_ENC_601`` and
 894 ``V4L2_QUANTIZATION_FULL_RANGE``.