linux-brain/Documentation/DocBook/media/v4l/pixfmt-yvu420m.xml

    <refentry id="V4L2-PIX-FMT-YVU420M">
      <refmeta>
	<refentrytitle>V4L2_PIX_FMT_YVU420M ('YM21')</refentrytitle>
	&manvol;
      </refmeta>
      <refnamediv>
	<refname> <constant>V4L2_PIX_FMT_YVU420M</constant></refname>
	<refpurpose>Variation of <constant>V4L2_PIX_FMT_YVU420</constant>
	  with planes non contiguous in memory. </refpurpose>
      </refnamediv>

      <refsect1>
	<title>Description</title>

	<para>This is a multi-planar format, as opposed to a packed format.
The three components are separated into three sub-images or planes.

The Y plane is first. The Y plane has one byte per pixel. The Cr data
constitutes the second plane which is half the width and half
the height of the Y plane (and of the image). Each Cr belongs to four
pixels, a two-by-two square of the image. For example,
Cr<subscript>0</subscript> belongs to Y'<subscript>00</subscript>,
Y'<subscript>01</subscript>, Y'<subscript>10</subscript>, and
Y'<subscript>11</subscript>. The Cb data, just like the Cr plane, constitutes
the third plane. </para>

	<para>If the Y plane has pad bytes after each row, then the Cr
and Cb planes have half as many pad bytes after their rows. In other
words, two Cx rows (including padding) is exactly as long as one Y row
(including padding).</para>

	<para><constant>V4L2_PIX_FMT_YVU420M</constant> is intended to be
used only in drivers and applications that support the multi-planar API,
described in <xref linkend="planar-apis"/>. </para>

	<example>
	  <title><constant>V4L2_PIX_FMT_YVU420M</constant> 4 &times; 4
pixel image</title>

	  <formalpara>
	    <title>Byte Order.</title>
	    <para>Each cell is one byte.
		<informaltable frame="none">
		<tgroup cols="5" align="center">
		  <colspec align="left" colwidth="2*" />
		  <tbody valign="top">
		    <row>
		      <entry>start0&nbsp;+&nbsp;0:</entry>
		      <entry>Y'<subscript>00</subscript></entry>
		      <entry>Y'<subscript>01</subscript></entry>
		      <entry>Y'<subscript>02</subscript></entry>
		      <entry>Y'<subscript>03</subscript></entry>
		    </row>
		    <row>
		      <entry>start0&nbsp;+&nbsp;4:</entry>
		      <entry>Y'<subscript>10</subscript></entry>
		      <entry>Y'<subscript>11</subscript></entry>
		      <entry>Y'<subscript>12</subscript></entry>
		      <entry>Y'<subscript>13</subscript></entry>
		    </row>
		    <row>
		      <entry>start0&nbsp;+&nbsp;8:</entry>
		      <entry>Y'<subscript>20</subscript></entry>
		      <entry>Y'<subscript>21</subscript></entry>
		      <entry>Y'<subscript>22</subscript></entry>
		      <entry>Y'<subscript>23</subscript></entry>
		    </row>
		    <row>
		      <entry>start0&nbsp;+&nbsp;12:</entry>
		      <entry>Y'<subscript>30</subscript></entry>
		      <entry>Y'<subscript>31</subscript></entry>
		      <entry>Y'<subscript>32</subscript></entry>
		      <entry>Y'<subscript>33</subscript></entry>
		    </row>
		    <row><entry></entry></row>
		    <row>
		      <entry>start1&nbsp;+&nbsp;0:</entry>
		      <entry>Cr<subscript>00</subscript></entry>
		      <entry>Cr<subscript>01</subscript></entry>
		    </row>
		    <row>
		      <entry>start1&nbsp;+&nbsp;2:</entry>
		      <entry>Cr<subscript>10</subscript></entry>
		      <entry>Cr<subscript>11</subscript></entry>
		    </row>
		    <row><entry></entry></row>
		    <row>
		      <entry>start2&nbsp;+&nbsp;0:</entry>
		      <entry>Cb<subscript>00</subscript></entry>
		      <entry>Cb<subscript>01</subscript></entry>
		    </row>
		    <row>
		      <entry>start2&nbsp;+&nbsp;2:</entry>
		      <entry>Cb<subscript>10</subscript></entry>
		      <entry>Cb<subscript>11</subscript></entry>
		    </row>
		  </tbody>
		</tgroup>
		</informaltable>
	      </para>
	  </formalpara>

	  <formalpara>
	    <title>Color Sample Location.</title>
	    <para>
		<informaltable frame="none">
		<tgroup cols="7" align="center">
		  <tbody valign="top">
		    <row>
		      <entry></entry>
		      <entry>0</entry><entry></entry><entry>1</entry><entry></entry>
		      <entry>2</entry><entry></entry><entry>3</entry>
		    </row>
		    <row>
		      <entry>0</entry>
		      <entry>Y</entry><entry></entry><entry>Y</entry><entry></entry>
		      <entry>Y</entry><entry></entry><entry>Y</entry>
		    </row>
		    <row>
		      <entry></entry>
		      <entry></entry><entry>C</entry><entry></entry><entry></entry>
		      <entry></entry><entry>C</entry><entry></entry>
		    </row>
		    <row>
		      <entry>1</entry>
		      <entry>Y</entry><entry></entry><entry>Y</entry><entry></entry>
		      <entry>Y</entry><entry></entry><entry>Y</entry>
		    </row>
		    <row>
		      <entry></entry>
		    </row>
		    <row>
		      <entry>2</entry>
		      <entry>Y</entry><entry></entry><entry>Y</entry><entry></entry>
		      <entry>Y</entry><entry></entry><entry>Y</entry>
		    </row>
		    <row>
		      <entry></entry>
		      <entry></entry><entry>C</entry><entry></entry><entry></entry>
		      <entry></entry><entry>C</entry><entry></entry>
		    </row>
		    <row>
		      <entry>3</entry>
		      <entry>Y</entry><entry></entry><entry>Y</entry><entry></entry>
		      <entry>Y</entry><entry></entry><entry>Y</entry>
		    </row>
		  </tbody>
		</tgroup>
		</informaltable>
	      </para>
	  </formalpara>
	</example>
      </refsect1>
    </refentry>