mirror of https://gitee.com/openkylin/linux.git
67 lines
2.6 KiB
XML
67 lines
2.6 KiB
XML
<refentry>
|
|
<refmeta>
|
|
<refentrytitle>V4L2_PIX_FMT_NV12MT ('TM12')</refentrytitle>
|
|
&manvol;
|
|
</refmeta>
|
|
<refnamediv>
|
|
<refname id="V4L2-PIX-FMT-NV12MT"><constant>V4L2_PIX_FMT_NV12MT
|
|
</constant></refname>
|
|
<refpurpose>Formats with ½ horizontal and vertical
|
|
chroma resolution. This format has two planes - one for luminance and one for
|
|
chrominance. Chroma samples are interleaved. The difference to
|
|
<constant>V4L2_PIX_FMT_NV12</constant> is the memory layout. Pixels are
|
|
grouped in macroblocks of 64x32 size. The order of macroblocks in memory is
|
|
also not standard.
|
|
</refpurpose>
|
|
</refnamediv>
|
|
<refsect1>
|
|
<title>Description</title>
|
|
|
|
<para>This is the two-plane versions of the YUV 4:2:0 format where data
|
|
is grouped into 64x32 macroblocks. The three components are separated into two
|
|
sub-images or planes. The Y plane has one byte per pixel and pixels are grouped
|
|
into 64x32 macroblocks. The CbCr plane has the same width, in bytes, as the Y
|
|
plane (and the image), but is half as tall in pixels. The chroma plane is also
|
|
grouped into 64x32 macroblocks.</para>
|
|
<para>Width of the buffer has to be aligned to the multiple of 128, and
|
|
height alignment is 32. Every four adjactent buffers - two horizontally and two
|
|
vertically are grouped together and are located in memory in Z or flipped Z
|
|
order. </para>
|
|
<para>Layout of macroblocks in memory is presented in the following
|
|
figure.</para>
|
|
<para><figure id="nv12mt">
|
|
<title><constant>V4L2_PIX_FMT_NV12MT</constant> macroblock Z shape
|
|
memory layout</title>
|
|
<mediaobject>
|
|
<imageobject>
|
|
<imagedata fileref="nv12mt.gif" format="GIF" />
|
|
</imageobject>
|
|
</mediaobject>
|
|
</figure>
|
|
The requirement that width is multiple of 128 is implemented because,
|
|
the Z shape cannot be cut in half horizontally. In case the vertical resolution
|
|
of macroblocks is odd then the last row of macroblocks is arranged in a linear
|
|
order. </para>
|
|
<para>In case of chroma the layout is identical. Cb and Cr samples are
|
|
interleaved. Height of the buffer is aligned to 32.
|
|
</para>
|
|
<example>
|
|
<title>Memory layout of macroblocks in <constant>V4L2_PIX_FMT_NV12
|
|
</constant> format pixel image - extreme case</title>
|
|
<para>
|
|
<figure id="nv12mt_ex">
|
|
<title>Example <constant>V4L2_PIX_FMT_NV12MT</constant> memory
|
|
layout of macroblocks</title>
|
|
<mediaobject>
|
|
<imageobject>
|
|
<imagedata fileref="nv12mt_example.gif" format="GIF" />
|
|
</imageobject>
|
|
</mediaobject>
|
|
</figure>
|
|
Memory layout of macroblocks of <constant>V4L2_PIX_FMT_NV12MT
|
|
</constant> format in most extreme case.
|
|
</para>
|
|
</example>
|
|
</refsect1>
|
|
</refentry>
|