linux-imx/Documentation/DocBook/media/v4l/pixfmt-nv12.xml

    <refentry>
      <refmeta>
	<refentrytitle>V4L2_PIX_FMT_NV12 ('NV12'), V4L2_PIX_FMT_NV21 ('NV21')</refentrytitle>
	&manvol;
      </refmeta>
      <refnamediv>
	<refname id="V4L2-PIX-FMT-NV12"><constant>V4L2_PIX_FMT_NV12</constant></refname>
	<refname id="V4L2-PIX-FMT-NV21"><constant>V4L2_PIX_FMT_NV21</constant></refname>
	<refpurpose>Formats with &frac12; horizontal and vertical
chroma resolution, also known as YUV 4:2:0. One luminance and one
chrominance plane with alternating chroma samples as opposed to
<constant>V4L2_PIX_FMT_YVU420</constant></refpurpose>
      </refnamediv>
      <refsect1>
	<title>Description</title>

	<para>These are two-plane versions of the YUV 4:2:0 format.
The three components are separated into two sub-images or planes. The
Y plane is first. The Y plane has one byte per pixel. For
<constant>V4L2_PIX_FMT_NV12</constant>, a combined CbCr plane
immediately follows the Y plane in memory.  The CbCr plane is the same
width, in bytes, as the Y plane (and of the image), but is half as
tall in pixels. Each CbCr pair belongs to four pixels. For example,
Cb<subscript>0</subscript>/Cr<subscript>0</subscript> belongs to
Y'<subscript>00</subscript>, Y'<subscript>01</subscript>,
Y'<subscript>10</subscript>, Y'<subscript>11</subscript>.
<constant>V4L2_PIX_FMT_NV21</constant> is the same except the Cb and
Cr bytes are swapped, the CrCb plane starts with a Cr byte.</para>

	<para>If the Y plane has pad bytes after each row, then the
CbCr plane has as many pad bytes after its rows.</para>

	<example>
	  <title><constant>V4L2_PIX_FMT_NV12</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>start&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>start&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>start&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>start&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>start&nbsp;+&nbsp;16:</entry>
		      <entry>Cb<subscript>00</subscript></entry>
		      <entry>Cr<subscript>00</subscript></entry>
		      <entry>Cb<subscript>01</subscript></entry>
		      <entry>Cr<subscript>01</subscript></entry>
		    </row>
		    <row>
		      <entry>start&nbsp;+&nbsp;20:</entry>
		      <entry>Cb<subscript>10</subscript></entry>
		      <entry>Cr<subscript>10</subscript></entry>
		      <entry>Cb<subscript>11</subscript></entry>
		      <entry>Cr<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>