1    <refentry id="V4L2-PIX-FMT-YUV420M">
2      <refmeta>
3	<refentrytitle>V4L2_PIX_FMT_YUV420M ('YM12')</refentrytitle>
4	&manvol;
5      </refmeta>
6      <refnamediv>
7	<refname> <constant>V4L2_PIX_FMT_YUV420M</constant></refname>
8	<refpurpose>Variation of <constant>V4L2_PIX_FMT_YUV420</constant>
9	  with planes non contiguous in memory. </refpurpose>
10      </refnamediv>
11
12      <refsect1>
13	<title>Description</title>
14
15	<para>This is a multi-planar format, as opposed to a packed format.
16The three components are separated into three sub- images or planes.
17
18The Y plane is first. The Y plane has one byte per pixel. The Cb data
19constitutes the second plane which is half the width and half
20the height of the Y plane (and of the image). Each Cb belongs to four
21pixels, a two-by-two square of the image. For example,
22Cb<subscript>0</subscript> belongs to Y'<subscript>00</subscript>,
23Y'<subscript>01</subscript>, Y'<subscript>10</subscript>, and
24Y'<subscript>11</subscript>. The Cr data, just like the Cb plane, is
25in the third plane. </para>
26
27	<para>If the Y plane has pad bytes after each row, then the Cb
28and Cr planes have half as many pad bytes after their rows. In other
29words, two Cx rows (including padding) is exactly as long as one Y row
30(including padding).</para>
31
32	<para><constant>V4L2_PIX_FMT_YUV420M</constant> is intended to be
33used only in drivers and applications that support the multi-planar API,
34described in <xref linkend="planar-apis"/>. </para>
35
36	<example>
37	  <title><constant>V4L2_PIX_FMT_YUV420M</constant> 4 &times; 4
38pixel image</title>
39
40	  <formalpara>
41	    <title>Byte Order.</title>
42	    <para>Each cell is one byte.
43		<informaltable frame="none">
44		<tgroup cols="5" align="center">
45		  <colspec align="left" colwidth="2*" />
46		  <tbody valign="top">
47		    <row>
48		      <entry>start0&nbsp;+&nbsp;0:</entry>
49		      <entry>Y'<subscript>00</subscript></entry>
50		      <entry>Y'<subscript>01</subscript></entry>
51		      <entry>Y'<subscript>02</subscript></entry>
52		      <entry>Y'<subscript>03</subscript></entry>
53		    </row>
54		    <row>
55		      <entry>start0&nbsp;+&nbsp;4:</entry>
56		      <entry>Y'<subscript>10</subscript></entry>
57		      <entry>Y'<subscript>11</subscript></entry>
58		      <entry>Y'<subscript>12</subscript></entry>
59		      <entry>Y'<subscript>13</subscript></entry>
60		    </row>
61		    <row>
62		      <entry>start0&nbsp;+&nbsp;8:</entry>
63		      <entry>Y'<subscript>20</subscript></entry>
64		      <entry>Y'<subscript>21</subscript></entry>
65		      <entry>Y'<subscript>22</subscript></entry>
66		      <entry>Y'<subscript>23</subscript></entry>
67		    </row>
68		    <row>
69		      <entry>start0&nbsp;+&nbsp;12:</entry>
70		      <entry>Y'<subscript>30</subscript></entry>
71		      <entry>Y'<subscript>31</subscript></entry>
72		      <entry>Y'<subscript>32</subscript></entry>
73		      <entry>Y'<subscript>33</subscript></entry>
74		    </row>
75		    <row><entry></entry></row>
76		    <row>
77		      <entry>start1&nbsp;+&nbsp;0:</entry>
78		      <entry>Cb<subscript>00</subscript></entry>
79		      <entry>Cb<subscript>01</subscript></entry>
80		    </row>
81		    <row>
82		      <entry>start1&nbsp;+&nbsp;2:</entry>
83		      <entry>Cb<subscript>10</subscript></entry>
84		      <entry>Cb<subscript>11</subscript></entry>
85		    </row>
86		    <row><entry></entry></row>
87		    <row>
88		      <entry>start2&nbsp;+&nbsp;0:</entry>
89		      <entry>Cr<subscript>00</subscript></entry>
90		      <entry>Cr<subscript>01</subscript></entry>
91		    </row>
92		    <row>
93		      <entry>start2&nbsp;+&nbsp;2:</entry>
94		      <entry>Cr<subscript>10</subscript></entry>
95		      <entry>Cr<subscript>11</subscript></entry>
96		    </row>
97		  </tbody>
98		</tgroup>
99		</informaltable>
100	      </para>
101	  </formalpara>
102
103	  <formalpara>
104	    <title>Color Sample Location.</title>
105	    <para>
106		<informaltable frame="none">
107		<tgroup cols="7" align="center">
108		  <tbody valign="top">
109		    <row>
110		      <entry></entry>
111		      <entry>0</entry><entry></entry><entry>1</entry><entry></entry>
112		      <entry>2</entry><entry></entry><entry>3</entry>
113		    </row>
114		    <row>
115		      <entry>0</entry>
116		      <entry>Y</entry><entry></entry><entry>Y</entry><entry></entry>
117		      <entry>Y</entry><entry></entry><entry>Y</entry>
118		    </row>
119		    <row>
120		      <entry></entry>
121		      <entry></entry><entry>C</entry><entry></entry><entry></entry>
122		      <entry></entry><entry>C</entry><entry></entry>
123		    </row>
124		    <row>
125		      <entry>1</entry>
126		      <entry>Y</entry><entry></entry><entry>Y</entry><entry></entry>
127		      <entry>Y</entry><entry></entry><entry>Y</entry>
128		    </row>
129		    <row>
130		      <entry></entry>
131		    </row>
132		    <row>
133		      <entry>2</entry>
134		      <entry>Y</entry><entry></entry><entry>Y</entry><entry></entry>
135		      <entry>Y</entry><entry></entry><entry>Y</entry>
136		    </row>
137		    <row>
138		      <entry></entry>
139		      <entry></entry><entry>C</entry><entry></entry><entry></entry>
140		      <entry></entry><entry>C</entry><entry></entry>
141		    </row>
142		    <row>
143		      <entry>3</entry>
144		      <entry>Y</entry><entry></entry><entry>Y</entry><entry></entry>
145		      <entry>Y</entry><entry></entry><entry>Y</entry>
146		    </row>
147		  </tbody>
148		</tgroup>
149		</informaltable>
150	      </para>
151	  </formalpara>
152	</example>
153      </refsect1>
154    </refentry>
155