| 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' = 0.299R' + 0.587G' + 0.114B' |
| 101 | |
| 102 | Cb = -0.169R' - 0.331G' + 0.5B' |
| 103 | |
| 104 | Cr = 0.5R' - 0.419G' - 0.081B' |
| 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} * (0.299R' + 0.587G' + 0.114B') + \frac{16}{256} |
| 245 | |
| 246 | Cb = \frac{224}{256} * (-0.169R' - 0.331G' + 0.5B') |
| 247 | |
| 248 | Cr = \frac{224}{256} * (0.5R' - 0.419G' - 0.081B') |
| 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_SYCC``. 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_SYCC`` encoding as defined by |
| 343 | :ref:`sycc`: |
| 344 | |
| 345 | .. math:: |
| 346 | |
| 347 | Y' = 0.2990R' + 0.5870G' + 0.1140B' |
| 348 | |
| 349 | Cb = -0.1687R' - 0.3313G' + 0.5B' |
| 350 | |
| 351 | Cr = 0.5R' - 0.4187G' - 0.0813B' |
| 352 | |
| 353 | Y' is clamped to the range [0…1] and Cb and Cr are clamped to the range |
| 354 | [-0.5…0.5]. The ``V4L2_YCBCR_ENC_SYCC`` quantization is always full |
| 355 | range. Although this Y'CbCr encoding looks very similar to the |
| 356 | ``V4L2_YCBCR_ENC_XV601`` encoding, it is not. The |
| 357 | ``V4L2_YCBCR_ENC_XV601`` scales and offsets the Y'CbCr values before |
| 358 | quantization, but this encoding does not do that. |
| 359 | |
| 360 | |
| 361 | .. _col-adobergb: |
| 362 | |
| 363 | Colorspace Adobe RGB (V4L2_COLORSPACE_ADOBERGB) |
| 364 | =============================================== |
| 365 | |
| 366 | The :ref:`adobergb` standard defines the colorspace used by computer |
| 367 | graphics that use the AdobeRGB colorspace. This is also known as the |
| 368 | :ref:`oprgb` standard. The default transfer function is |
| 369 | ``V4L2_XFER_FUNC_ADOBERGB``. The default Y'CbCr encoding is |
| 370 | ``V4L2_YCBCR_ENC_601``. The default Y'CbCr quantization is limited |
| 371 | range. The chromaticities of the primary colors and the white reference |
| 372 | are: |
| 373 | |
| 374 | |
| 375 | |
| 376 | .. tabularcolumns:: |p{4.4cm}|p{4.4cm}|p{8.7cm}| |
| 377 | |
| 378 | .. flat-table:: Adobe RGB Chromaticities |
| 379 | :header-rows: 1 |
| 380 | :stub-columns: 0 |
| 381 | :widths: 1 1 2 |
| 382 | |
| 383 | |
| 384 | - .. row 1 |
| 385 | |
| 386 | - Color |
| 387 | |
| 388 | - x |
| 389 | |
| 390 | - y |
| 391 | |
| 392 | - .. row 2 |
| 393 | |
| 394 | - Red |
| 395 | |
| 396 | - 0.6400 |
| 397 | |
| 398 | - 0.3300 |
| 399 | |
| 400 | - .. row 3 |
| 401 | |
| 402 | - Green |
| 403 | |
| 404 | - 0.2100 |
| 405 | |
| 406 | - 0.7100 |
| 407 | |
| 408 | - .. row 4 |
| 409 | |
| 410 | - Blue |
| 411 | |
| 412 | - 0.1500 |
| 413 | |
| 414 | - 0.0600 |
| 415 | |
| 416 | - .. row 5 |
| 417 | |
| 418 | - White Reference (D65) |
| 419 | |
| 420 | - 0.3127 |
| 421 | |
| 422 | - 0.3290 |
| 423 | |
| 424 | |
| 425 | |
| 426 | Transfer function: |
| 427 | |
| 428 | .. math:: |
| 429 | |
| 430 | L' = L ^{\frac{1}{2.19921875}} |
| 431 | |
| 432 | Inverse Transfer function: |
| 433 | |
| 434 | .. math:: |
| 435 | |
| 436 | L = L'^{(2.19921875)} |
| 437 | |
| 438 | The luminance (Y') and color difference (Cb and Cr) are obtained with |
| 439 | the following ``V4L2_YCBCR_ENC_601`` encoding: |
| 440 | |
| 441 | .. math:: |
| 442 | |
| 443 | Y' = 0.299R' + 0.587G' + 0.114B' |
| 444 | |
| 445 | Cb = -0.169R' - 0.331G' + 0.5B' |
| 446 | |
| 447 | Cr = 0.5R' - 0.419G' - 0.081B' |
| 448 | |
| 449 | Y' is clamped to the range [0…1] and Cb and Cr are clamped to the range |
| 450 | [-0.5…0.5]. This transform is identical to one defined in SMPTE |
| 451 | 170M/BT.601. The Y'CbCr quantization is limited range. |
| 452 | |
| 453 | |
| 454 | .. _col-bt2020: |
| 455 | |
| 456 | Colorspace BT.2020 (V4L2_COLORSPACE_BT2020) |
| 457 | =========================================== |
| 458 | |
| 459 | The :ref:`itu2020` standard defines the colorspace used by Ultra-high |
| 460 | definition television (UHDTV). The default transfer function is |
| 461 | ``V4L2_XFER_FUNC_709``. The default Y'CbCr encoding is |
| 462 | ``V4L2_YCBCR_ENC_BT2020``. The default R'G'B' quantization is limited |
| 463 | range (!), and so is the default Y'CbCr quantization. The chromaticities |
| 464 | of the primary colors and the white reference are: |
| 465 | |
| 466 | |
| 467 | |
| 468 | .. tabularcolumns:: |p{4.4cm}|p{4.4cm}|p{8.7cm}| |
| 469 | |
| 470 | .. flat-table:: BT.2020 Chromaticities |
| 471 | :header-rows: 1 |
| 472 | :stub-columns: 0 |
| 473 | :widths: 1 1 2 |
| 474 | |
| 475 | |
| 476 | - .. row 1 |
| 477 | |
| 478 | - Color |
| 479 | |
| 480 | - x |
| 481 | |
| 482 | - y |
| 483 | |
| 484 | - .. row 2 |
| 485 | |
| 486 | - Red |
| 487 | |
| 488 | - 0.708 |
| 489 | |
| 490 | - 0.292 |
| 491 | |
| 492 | - .. row 3 |
| 493 | |
| 494 | - Green |
| 495 | |
| 496 | - 0.170 |
| 497 | |
| 498 | - 0.797 |
| 499 | |
| 500 | - .. row 4 |
| 501 | |
| 502 | - Blue |
| 503 | |
| 504 | - 0.131 |
| 505 | |
| 506 | - 0.046 |
| 507 | |
| 508 | - .. row 5 |
| 509 | |
| 510 | - White Reference (D65) |
| 511 | |
| 512 | - 0.3127 |
| 513 | |
| 514 | - 0.3290 |
| 515 | |
| 516 | |
| 517 | |
| 518 | Transfer function (same as Rec. 709): |
| 519 | |
| 520 | .. math:: |
| 521 | |
| 522 | L' = 4.5L\text{, for }0 \le L < 0.018 |
| 523 | |
| 524 | L' = 1.099L ^{0.45} - 0.099\text{, for } 0.018 \le L \le 1 |
| 525 | |
| 526 | Inverse Transfer function: |
| 527 | |
| 528 | .. math:: |
| 529 | |
| 530 | L = L' / 4.5\text{, for } L' < 0.081 |
| 531 | |
| 532 | L = \left( \frac{L' + 0.099}{1.099}\right) ^{\frac{1}{0.45} }\text{, for } L' \ge 0.081 |
| 533 | |
| 534 | The luminance (Y') and color difference (Cb and Cr) are obtained with |
| 535 | the following ``V4L2_YCBCR_ENC_BT2020`` encoding: |
| 536 | |
| 537 | .. math:: |
| 538 | |
| 539 | Y' = 0.2627R' + 0.6780G' + 0.0593B' |
| 540 | |
| 541 | Cb = -0.1396R' - 0.3604G' + 0.5B' |
| 542 | |
| 543 | Cr = 0.5R' - 0.4598G' - 0.0402B' |
| 544 | |
| 545 | Y' is clamped to the range [0…1] and Cb and Cr are clamped to the range |
| 546 | [-0.5…0.5]. The Y'CbCr quantization is limited range. |
| 547 | |
| 548 | There is also an alternate constant luminance R'G'B' to Yc'CbcCrc |
| 549 | (``V4L2_YCBCR_ENC_BT2020_CONST_LUM``) encoding: |
| 550 | |
| 551 | Luma: |
| 552 | |
| 553 | .. math:: |
| 554 | :nowrap: |
| 555 | |
| 556 | \begin{align*} |
| 557 | Yc' = (0.2627R + 0.6780G + 0.0593B)'& \\ |
| 558 | B' - Yc' \le 0:& \\ |
| 559 | &Cbc = (B' - Yc') / 1.9404 \\ |
| 560 | B' - Yc' > 0: & \\ |
| 561 | &Cbc = (B' - Yc') / 1.5816 \\ |
| 562 | R' - Yc' \le 0:& \\ |
| 563 | &Crc = (R' - Y') / 1.7184 \\ |
| 564 | R' - Yc' > 0:& \\ |
| 565 | &Crc = (R' - Y') / 0.9936 |
| 566 | \end{align*} |
| 567 | |
| 568 | Yc' is clamped to the range [0…1] and Cbc and Crc are clamped to the |
| 569 | range [-0.5…0.5]. The Yc'CbcCrc quantization is limited range. |
| 570 | |
| 571 | |
| 572 | .. _col-dcip3: |
| 573 | |
| 574 | Colorspace DCI-P3 (V4L2_COLORSPACE_DCI_P3) |
| 575 | ========================================== |
| 576 | |
| 577 | The :ref:`smpte431` standard defines the colorspace used by cinema |
| 578 | projectors that use the DCI-P3 colorspace. The default transfer function |
| 579 | is ``V4L2_XFER_FUNC_DCI_P3``. The default Y'CbCr encoding is |
| 580 | ``V4L2_YCBCR_ENC_709``. |
| 581 | |
| 582 | .. note:: |
| 583 | |
| 584 | Note that this colorspace does not specify a |
| 585 | Y'CbCr encoding since it is not meant to be encoded to Y'CbCr. So this |
| 586 | default Y'CbCr encoding was picked because it is the HDTV encoding. The |
| 587 | default Y'CbCr quantization is limited range. The chromaticities of the |
| 588 | primary colors and the white reference are: |
| 589 | |
| 590 | |
| 591 | |
| 592 | .. tabularcolumns:: |p{4.4cm}|p{4.4cm}|p{8.7cm}| |
| 593 | |
| 594 | .. flat-table:: DCI-P3 Chromaticities |
| 595 | :header-rows: 1 |
| 596 | :stub-columns: 0 |
| 597 | :widths: 1 1 2 |
| 598 | |
| 599 | |
| 600 | - .. row 1 |
| 601 | |
| 602 | - Color |
| 603 | |
| 604 | - x |
| 605 | |
| 606 | - y |
| 607 | |
| 608 | - .. row 2 |
| 609 | |
| 610 | - Red |
| 611 | |
| 612 | - 0.6800 |
| 613 | |
| 614 | - 0.3200 |
| 615 | |
| 616 | - .. row 3 |
| 617 | |
| 618 | - Green |
| 619 | |
| 620 | - 0.2650 |
| 621 | |
| 622 | - 0.6900 |
| 623 | |
| 624 | - .. row 4 |
| 625 | |
| 626 | - Blue |
| 627 | |
| 628 | - 0.1500 |
| 629 | |
| 630 | - 0.0600 |
| 631 | |
| 632 | - .. row 5 |
| 633 | |
| 634 | - White Reference |
| 635 | |
| 636 | - 0.3140 |
| 637 | |
| 638 | - 0.3510 |
| 639 | |
| 640 | |
| 641 | |
| 642 | Transfer function: |
| 643 | |
| 644 | .. math:: |
| 645 | |
| 646 | L' = L^{\frac{1}{2.6}} |
| 647 | |
| 648 | Inverse Transfer function: |
| 649 | |
| 650 | .. math:: |
| 651 | |
| 652 | L = L'^{(2.6)} |
| 653 | |
| 654 | Y'CbCr encoding is not specified. V4L2 defaults to Rec. 709. |
| 655 | |
| 656 | |
| 657 | .. _col-smpte-240m: |
| 658 | |
| 659 | Colorspace SMPTE 240M (V4L2_COLORSPACE_SMPTE240M) |
| 660 | ================================================= |
| 661 | |
| 662 | The :ref:`smpte240m` standard was an interim standard used during the |
| 663 | early days of HDTV (1988-1998). It has been superseded by Rec. 709. The |
| 664 | default transfer function is ``V4L2_XFER_FUNC_SMPTE240M``. The default |
| 665 | Y'CbCr encoding is ``V4L2_YCBCR_ENC_SMPTE240M``. The default Y'CbCr |
| 666 | quantization is limited range. The chromaticities of the primary colors |
| 667 | and the white reference are: |
| 668 | |
| 669 | |
| 670 | |
| 671 | .. tabularcolumns:: |p{4.4cm}|p{4.4cm}|p{8.7cm}| |
| 672 | |
| 673 | .. flat-table:: SMPTE 240M Chromaticities |
| 674 | :header-rows: 1 |
| 675 | :stub-columns: 0 |
| 676 | :widths: 1 1 2 |
| 677 | |
| 678 | |
| 679 | - .. row 1 |
| 680 | |
| 681 | - Color |
| 682 | |
| 683 | - x |
| 684 | |
| 685 | - y |
| 686 | |
| 687 | - .. row 2 |
| 688 | |
| 689 | - Red |
| 690 | |
| 691 | - 0.630 |
| 692 | |
| 693 | - 0.340 |
| 694 | |
| 695 | - .. row 3 |
| 696 | |
| 697 | - Green |
| 698 | |
| 699 | - 0.310 |
| 700 | |
| 701 | - 0.595 |
| 702 | |
| 703 | - .. row 4 |
| 704 | |
| 705 | - Blue |
| 706 | |
| 707 | - 0.155 |
| 708 | |
| 709 | - 0.070 |
| 710 | |
| 711 | - .. row 5 |
| 712 | |
| 713 | - White Reference (D65) |
| 714 | |
| 715 | - 0.3127 |
| 716 | |
| 717 | - 0.3290 |
| 718 | |
| 719 | |
| 720 | These chromaticities are identical to the SMPTE 170M colorspace. |
| 721 | |
| 722 | Transfer function: |
| 723 | |
| 724 | .. math:: |
| 725 | |
| 726 | L' = 4L\text{, for } 0 \le L < 0.0228 |
| 727 | |
| 728 | L' = 1.1115L ^{0.45} - 0.1115\text{, for } 0.0228 \le L \le 1 |
| 729 | |
| 730 | Inverse Transfer function: |
| 731 | |
| 732 | .. math:: |
| 733 | |
| 734 | L = \frac{L'}{4}\text{, for } 0 \le L' < 0.0913 |
| 735 | |
| 736 | L = \left( \frac{L' + 0.1115}{1.1115}\right) ^{\frac{1}{0.45} }\text{, for } L' \ge 0.0913 |
| 737 | |
| 738 | The luminance (Y') and color difference (Cb and Cr) are obtained with |
| 739 | the following ``V4L2_YCBCR_ENC_SMPTE240M`` encoding: |
| 740 | |
| 741 | .. math:: |
| 742 | |
| 743 | Y' = 0.2122R' + 0.7013G' + 0.0865B' |
| 744 | |
| 745 | Cb = -0.1161R' - 0.3839G' + 0.5B' |
| 746 | |
| 747 | Cr = 0.5R' - 0.4451G' - 0.0549B' |
| 748 | |
| 749 | Yc' is clamped to the range [0…1] and Cbc and Crc are clamped to the |
| 750 | range [-0.5…0.5]. The Y'CbCr quantization is limited range. |
| 751 | |
| 752 | |
| 753 | .. _col-sysm: |
| 754 | |
| 755 | Colorspace NTSC 1953 (V4L2_COLORSPACE_470_SYSTEM_M) |
| 756 | =================================================== |
| 757 | |
| 758 | This standard defines the colorspace used by NTSC in 1953. In practice |
| 759 | this colorspace is obsolete and SMPTE 170M should be used instead. The |
| 760 | default transfer function is ``V4L2_XFER_FUNC_709``. The default Y'CbCr |
| 761 | encoding is ``V4L2_YCBCR_ENC_601``. The default Y'CbCr quantization is |
| 762 | limited range. The chromaticities of the primary colors and the white |
| 763 | reference are: |
| 764 | |
| 765 | |
| 766 | |
| 767 | .. tabularcolumns:: |p{4.4cm}|p{4.4cm}|p{8.7cm}| |
| 768 | |
| 769 | .. flat-table:: NTSC 1953 Chromaticities |
| 770 | :header-rows: 1 |
| 771 | :stub-columns: 0 |
| 772 | :widths: 1 1 2 |
| 773 | |
| 774 | |
| 775 | - .. row 1 |
| 776 | |
| 777 | - Color |
| 778 | |
| 779 | - x |
| 780 | |
| 781 | - y |
| 782 | |
| 783 | - .. row 2 |
| 784 | |
| 785 | - Red |
| 786 | |
| 787 | - 0.67 |
| 788 | |
| 789 | - 0.33 |
| 790 | |
| 791 | - .. row 3 |
| 792 | |
| 793 | - Green |
| 794 | |
| 795 | - 0.21 |
| 796 | |
| 797 | - 0.71 |
| 798 | |
| 799 | - .. row 4 |
| 800 | |
| 801 | - Blue |
| 802 | |
| 803 | - 0.14 |
| 804 | |
| 805 | - 0.08 |
| 806 | |
| 807 | - .. row 5 |
| 808 | |
| 809 | - White Reference (C) |
| 810 | |
| 811 | - 0.310 |
| 812 | |
| 813 | - 0.316 |
| 814 | |
| 815 | |
| 816 | .. note:: |
| 817 | |
| 818 | This colorspace uses Illuminant C instead of D65 as the white |
| 819 | reference. To correctly convert an image in this colorspace to another |
| 820 | that uses D65 you need to apply a chromatic adaptation algorithm such as |
| 821 | the Bradford method. |
| 822 | |
| 823 | The transfer function was never properly defined for NTSC 1953. The Rec. |
| 824 | 709 transfer function is recommended in the literature: |
| 825 | |
| 826 | .. math:: |
| 827 | |
| 828 | L' = 4.5L\text{, for } 0 \le L < 0.018 |
| 829 | |
| 830 | L' = 1.099L ^{0.45} - 0.099\text{, for } 0.018 \le L \le 1 |
| 831 | |
| 832 | Inverse Transfer function: |
| 833 | |
| 834 | .. math:: |
| 835 | |
| 836 | L = \frac{L'}{4.5} \text{, for } L' < 0.081 |
| 837 | |
| 838 | L = \left( \frac{L' + 0.099}{1.099}\right) ^{\frac{1}{0.45} }\text{, for } L' \ge 0.081 |
| 839 | |
| 840 | The luminance (Y') and color difference (Cb and Cr) are obtained with |
| 841 | the following ``V4L2_YCBCR_ENC_601`` encoding: |
| 842 | |
| 843 | .. math:: |
| 844 | |
| 845 | Y' = 0.299R' + 0.587G' + 0.114B' |
| 846 | |
| 847 | Cb = -0.169R' - 0.331G' + 0.5B' |
| 848 | |
| 849 | Cr = 0.5R' - 0.419G' - 0.081B' |
| 850 | |
| 851 | Y' is clamped to the range [0…1] and Cb and Cr are clamped to the range |
| 852 | [-0.5…0.5]. The Y'CbCr quantization is limited range. This transform is |
| 853 | identical to one defined in SMPTE 170M/BT.601. |
| 854 | |
| 855 | |
| 856 | .. _col-sysbg: |
| 857 | |
| 858 | Colorspace EBU Tech. 3213 (V4L2_COLORSPACE_470_SYSTEM_BG) |
| 859 | ========================================================= |
| 860 | |
| 861 | The :ref:`tech3213` standard defines the colorspace used by PAL/SECAM |
| 862 | in 1975. In practice this colorspace is obsolete and SMPTE 170M should |
| 863 | be used instead. The default transfer function is |
| 864 | ``V4L2_XFER_FUNC_709``. The default Y'CbCr encoding is |
| 865 | ``V4L2_YCBCR_ENC_601``. The default Y'CbCr quantization is limited |
| 866 | range. The chromaticities of the primary colors and the white reference |
| 867 | are: |
| 868 | |
| 869 | |
| 870 | |
| 871 | .. tabularcolumns:: |p{4.4cm}|p{4.4cm}|p{8.7cm}| |
| 872 | |
| 873 | .. flat-table:: EBU Tech. 3213 Chromaticities |
| 874 | :header-rows: 1 |
| 875 | :stub-columns: 0 |
| 876 | :widths: 1 1 2 |
| 877 | |
| 878 | |
| 879 | - .. row 1 |
| 880 | |
| 881 | - Color |
| 882 | |
| 883 | - x |
| 884 | |
| 885 | - y |
| 886 | |
| 887 | - .. row 2 |
| 888 | |
| 889 | - Red |
| 890 | |
| 891 | - 0.64 |
| 892 | |
| 893 | - 0.33 |
| 894 | |
| 895 | - .. row 3 |
| 896 | |
| 897 | - Green |
| 898 | |
| 899 | - 0.29 |
| 900 | |
| 901 | - 0.60 |
| 902 | |
| 903 | - .. row 4 |
| 904 | |
| 905 | - Blue |
| 906 | |
| 907 | - 0.15 |
| 908 | |
| 909 | - 0.06 |
| 910 | |
| 911 | - .. row 5 |
| 912 | |
| 913 | - White Reference (D65) |
| 914 | |
| 915 | - 0.3127 |
| 916 | |
| 917 | - 0.3290 |
| 918 | |
| 919 | |
| 920 | |
| 921 | The transfer function was never properly defined for this colorspace. |
| 922 | The Rec. 709 transfer function is recommended in the literature: |
| 923 | |
| 924 | .. math:: |
| 925 | |
| 926 | L' = 4.5L\text{, for } 0 \le L < 0.018 |
| 927 | |
| 928 | L' = 1.099L ^{0.45} - 0.099\text{, for } 0.018 \le L \le 1 |
| 929 | |
| 930 | Inverse Transfer function: |
| 931 | |
| 932 | .. math:: |
| 933 | |
| 934 | L = \frac{L'}{4.5} \text{, for } L' < 0.081 |
| 935 | |
| 936 | L = \left(\frac{L' + 0.099}{1.099} \right) ^{\frac{1}{0.45} }\text{, for } L' \ge 0.081 |
| 937 | |
| 938 | The luminance (Y') and color difference (Cb and Cr) are obtained with |
| 939 | the following ``V4L2_YCBCR_ENC_601`` encoding: |
| 940 | |
| 941 | .. math:: |
| 942 | |
| 943 | Y' = 0.299R' + 0.587G' + 0.114B' |
| 944 | |
| 945 | Cb = -0.169R' - 0.331G' + 0.5B' |
| 946 | |
| 947 | Cr = 0.5R' - 0.419G' - 0.081B' |
| 948 | |
| 949 | Y' is clamped to the range [0…1] and Cb and Cr are clamped to the range |
| 950 | [-0.5…0.5]. The Y'CbCr quantization is limited range. This transform is |
| 951 | identical to one defined in SMPTE 170M/BT.601. |
| 952 | |
| 953 | |
| 954 | .. _col-jpeg: |
| 955 | |
| 956 | Colorspace JPEG (V4L2_COLORSPACE_JPEG) |
| 957 | ====================================== |
| 958 | |
| 959 | This colorspace defines the colorspace used by most (Motion-)JPEG |
| 960 | formats. The chromaticities of the primary colors and the white |
| 961 | reference are identical to sRGB. The transfer function use is |
| 962 | ``V4L2_XFER_FUNC_SRGB``. The Y'CbCr encoding is ``V4L2_YCBCR_ENC_601`` |
| 963 | with full range quantization where Y' is scaled to [0…255] and Cb/Cr are |
| 964 | scaled to [-128…128] and then clipped to [-128…127]. |
| 965 | |
| 966 | .. note:: |
| 967 | |
| 968 | The JPEG standard does not actually store colorspace |
| 969 | information. So if something other than sRGB is used, then the driver |
| 970 | will have to set that information explicitly. Effectively |
| 971 | ``V4L2_COLORSPACE_JPEG`` can be considered to be an abbreviation for |
| 972 | ``V4L2_COLORSPACE_SRGB``, ``V4L2_YCBCR_ENC_601`` and |
| 973 | ``V4L2_QUANTIZATION_FULL_RANGE``. |