projects / deliverable / linux.git / blame
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|---|---|---|
| 5377d91f MH |
1 | .. -*- coding: utf-8; mode: rst -*- |
| 2 | ||
| 3 | .. _V4L2-PIX-FMT-NV12MT: | |
| 4 | ||
| 5 | **************************** | |
| 6 | V4L2_PIX_FMT_NV12MT ('TM12') | |
| 7 | **************************** | |
| 8 | ||
| 9 | *man V4L2_PIX_FMT_NV12MT(2)* | |
| 10 | ||
| 11 | Formats with ½ horizontal and vertical chroma resolution. This format | |
| 12 | has two planes - one for luminance and one for chrominance. Chroma | |
| 13 | samples are interleaved. The difference to ``V4L2_PIX_FMT_NV12`` is the | |
| 14 | memory layout. Pixels are grouped in macroblocks of 64x32 size. The | |
| 15 | order of macroblocks in memory is also not standard. | |
| 16 | ||
| 17 | ||
| 18 | Description | |
| 19 | =========== | |
| 20 | ||
| 21 | This is the two-plane versions of the YUV 4:2:0 format where data is | |
| 22 | grouped into 64x32 macroblocks. The three components are separated into | |
| 23 | two sub-images or planes. The Y plane has one byte per pixel and pixels | |
| 24 | are grouped into 64x32 macroblocks. The CbCr plane has the same width, | |
| 25 | in bytes, as the Y plane (and the image), but is half as tall in pixels. | |
| 26 | The chroma plane is also grouped into 64x32 macroblocks. | |
| 27 | ||
| 28 | Width of the buffer has to be aligned to the multiple of 128, and height | |
| 29 | alignment is 32. Every four adjacent buffers - two horizontally and two | |
| 30 | vertically are grouped together and are located in memory in Z or | |
| 31 | flipped Z order. | |
| 32 | ||
| 33 | Layout of macroblocks in memory is presented in the following figure. | |
| 34 | ||
| 35 | ||
| 36 | .. _nv12mt: | |
| 37 | ||
| 38 | .. figure:: pixfmt-nv12mt_files/nv12mt.* | |
| 39 | :alt: nv12mt.gif | |
| 40 | :align: center | |
| 41 | ||
| 42 | V4L2_PIX_FMT_NV12MT macroblock Z shape memory layout | |
| 43 | ||
| 44 | The requirement that width is multiple of 128 is implemented because, | |
| 45 | the Z shape cannot be cut in half horizontally. In case the vertical | |
| 46 | resolution of macroblocks is odd then the last row of macroblocks is | |
| 47 | arranged in a linear order. | |
| 48 | ||
| 49 | In case of chroma the layout is identical. Cb and Cr samples are | |
| 50 | interleaved. Height of the buffer is aligned to 32. | |
| 51 | ||
| 52 | ||
| 53 | .. _nv12mt_ex: | |
| 54 | ||
| 55 | .. figure:: pixfmt-nv12mt_files/nv12mt_example.* | |
| 56 | :alt: nv12mt_example.gif | |
| 57 | :align: center | |
| 58 | ||
| 59 | Example V4L2_PIX_FMT_NV12MT memory layout of macroblocks | |
| 60 | ||
| 61 | Memory layout of macroblocks of ``V4L2_PIX_FMT_NV12MT`` format in most | |
| 62 | extreme case. |