blob: 7a2855a526c1119a734a5c5a6d1b30f4de66c0c5 (
plain) (
blame)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
|
<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>
<!--
Local Variables:
mode: sgml
sgml-parent-document: "pixfmt.sgml"
indent-tabs-mode: nil
End:
-->
|
