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diff --git a/Documentation/userspace-api/media/v4l/yuv-formats.rst b/Documentation/userspace-api/media/v4l/yuv-formats.rst new file mode 100644 index 0000000000..24b34cdfa6 --- /dev/null +++ b/Documentation/userspace-api/media/v4l/yuv-formats.rst @@ -0,0 +1,273 @@ +.. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later + +.. _yuv-formats: + +*********** +YUV Formats +*********** + +YUV is the format native to TV broadcast and composite video signals. It +separates the brightness information (Y) from the color information (U +and V or Cb and Cr). The color information consists of red and blue +*color difference* signals, this way the green component can be +reconstructed by subtracting from the brightness component. See +:ref:`colorspaces` for conversion examples. YUV was chosen because +early television would only transmit brightness information. To add +color in a way compatible with existing receivers a new signal carrier +was added to transmit the color difference signals. + + +Subsampling +=========== + +YUV formats commonly encode images with a lower resolution for the chroma +components than for the luma component. This compression technique, taking +advantage of the human eye being more sensitive to luminance than color +differences, is called chroma subsampling. + +While many combinations of subsampling factors in the horizontal and vertical +direction are possible, common factors are 1 (no subsampling), 2 and 4, with +horizontal subsampling always larger than or equal to vertical subsampling. +Common combinations are named as follows. + +- `4:4:4`: No subsampling +- `4:2:2`: Horizontal subsampling by 2, no vertical subsampling +- `4:2:0`: Horizontal subsampling by 2, vertical subsampling by 2 +- `4:1:1`: Horizontal subsampling by 4, no vertical subsampling +- `4:1:0`: Horizontal subsampling by 4, vertical subsampling by 4 + +Subsampling the chroma component effectively creates chroma values that can be +located in different spatial locations: + +- .. _yuv-chroma-centered: + + The subsampled chroma value may be calculated by simply averaging the chroma + value of two consecutive pixels. It effectively models the chroma of a pixel + sited between the two original pixels. This is referred to as centered or + interstitially sited chroma. + +- .. _yuv-chroma-cosited: + + The other option is to subsample chroma values in a way that place them in + the same spatial sites as the pixels. This may be performed by skipping every + other chroma sample (creating aliasing artifacts), or with filters using an + odd number of taps. This is referred to as co-sited chroma. + +The following examples show different combination of chroma siting in a 4x4 +image. + +.. flat-table:: 4:2:2 subsampling, interstitially sited + :header-rows: 1 + :stub-columns: 1 + + * - + - 0 + - + - 1 + - + - 2 + - + - 3 + * - 0 + - Y + - C + - Y + - + - Y + - C + - Y + * - 1 + - Y + - C + - Y + - + - Y + - C + - Y + * - 2 + - Y + - C + - Y + - + - Y + - C + - Y + * - 3 + - Y + - C + - Y + - + - Y + - C + - Y + +.. flat-table:: 4:2:2 subsampling, co-sited + :header-rows: 1 + :stub-columns: 1 + + * - + - 0 + - + - 1 + - + - 2 + - + - 3 + * - 0 + - Y/C + - + - Y + - + - Y/C + - + - Y + * - 1 + - Y/C + - + - Y + - + - Y/C + - + - Y + * - 2 + - Y/C + - + - Y + - + - Y/C + - + - Y + * - 3 + - Y/C + - + - Y + - + - Y/C + - + - Y + +.. flat-table:: 4:2:0 subsampling, horizontally interstitially sited, vertically co-sited + :header-rows: 1 + :stub-columns: 1 + + * - + - 0 + - + - 1 + - + - 2 + - + - 3 + * - 0 + - Y + - C + - Y + - + - Y + - C + - Y + * - 1 + - Y + - + - Y + - + - Y + - + - Y + * - 2 + - Y + - C + - Y + - + - Y + - C + - Y + * - 3 + - Y + - + - Y + - + - Y + - + - Y + +.. flat-table:: 4:1:0 subsampling, horizontally and vertically interstitially sited + :header-rows: 1 + :stub-columns: 1 + + * - + - 0 + - + - 1 + - + - 2 + - + - 3 + * - 0 + - Y + - + - Y + - + - Y + - + - Y + * - + - + - + - + - + - + - + - + * - 1 + - Y + - + - Y + - + - Y + - + - Y + * - + - + - + - + - C + - + - + - + * - 2 + - Y + - + - Y + - + - Y + - + - Y + * - + - + - + - + - + - + - + - + * - 3 + - Y + - + - Y + - + - Y + - + - Y + + +.. toctree:: + :maxdepth: 1 + + pixfmt-packed-yuv + pixfmt-yuv-planar + pixfmt-yuv-luma + pixfmt-y8i + pixfmt-y12i + pixfmt-uv8 + pixfmt-m420 |