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Diffstat (limited to 'Documentation/userspace-api/media/v4l/yuv-formats.rst')
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1 files changed, 247 insertions, 31 deletions
diff --git a/Documentation/userspace-api/media/v4l/yuv-formats.rst b/Documentation/userspace-api/media/v4l/yuv-formats.rst index 4a05a105a9e6..24b34cdfa6fe 100644 --- a/Documentation/userspace-api/media/v4l/yuv-formats.rst +++ b/Documentation/userspace-api/media/v4l/yuv-formats.rst @@ -14,44 +14,260 @@ 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. Secondary in the YUV -format the U and V components usually have lower resolution than the Y -component. This is an analog video compression technique taking -advantage of a property of the human visual system, being more sensitive -to brightness information. +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-grey - pixfmt-y10 - pixfmt-y12 - pixfmt-y14 - pixfmt-y10b - pixfmt-y10p - pixfmt-y16 - pixfmt-y16-be + pixfmt-yuv-planar + pixfmt-yuv-luma pixfmt-y8i pixfmt-y12i pixfmt-uv8 - pixfmt-yuyv - pixfmt-uyvy - pixfmt-yvyu - pixfmt-vyuy - pixfmt-y41p - pixfmt-yuv420 - pixfmt-yuv420m - pixfmt-yuv422m - pixfmt-yuv444m - pixfmt-yuv410 - pixfmt-yuv422p - pixfmt-yuv411p - pixfmt-nv12 - pixfmt-nv12m - pixfmt-nv12mt - pixfmt-nv16 - pixfmt-nv16m - pixfmt-nv24 pixfmt-m420 |