Documentation/DocBook/v4l/pixfmt-nv12.xml

   1     <refentry>
   2       <refmeta>
   3         <refentrytitle>V4L2_PIX_FMT_NV12 ('NV12'), V4L2_PIX_FMT_NV21 ('NV21')</refentrytitle>
   4         &manvol;
   5       </refmeta>
   6       <refnamediv>
   7         <refname id="V4L2-PIX-FMT-NV12"><constant>V4L2_PIX_FMT_NV12</constant></refname>
   8         <refname id="V4L2-PIX-FMT-NV21"><constant>V4L2_PIX_FMT_NV21</constant></refname>
   9         <refpurpose>Formats with &frac12; horizontal and vertical
  10 chroma resolution, also known as YUV 4:2:0. One luminance and one
  11 chrominance plane with alternating chroma samples as opposed to
  12 <constant>V4L2_PIX_FMT_YVU420</constant></refpurpose>
  13       </refnamediv>
  14       <refsect1>
  15         <title>Description</title>
  16
  17         <para>These are two-plane versions of the YUV 4:2:0 format.
  18 The three components are separated into two sub-images or planes. The
  19 Y plane is first. The Y plane has one byte per pixel. For
  20 <constant>V4L2_PIX_FMT_NV12</constant>, a combined CbCr plane
  21 immediately follows the Y plane in memory.  The CbCr plane is the same
  22 width, in bytes, as the Y plane (and of the image), but is half as
  23 tall in pixels. Each CbCr pair belongs to four pixels. For example,
  24 Cb<subscript>0</subscript>/Cr<subscript>0</subscript> belongs to
  25 Y'<subscript>00</subscript>, Y'<subscript>01</subscript>,
  26 Y'<subscript>10</subscript>, Y'<subscript>11</subscript>.
  27 <constant>V4L2_PIX_FMT_NV21</constant> is the same except the Cb and
  28 Cr bytes are swapped, the CrCb plane starts with a Cr byte.</para>
  29
  30         <para>If the Y plane has pad bytes after each row, then the
  31 CbCr plane has as many pad bytes after its rows.</para>
  32
  33         <example>
  34           <title><constant>V4L2_PIX_FMT_NV12</constant> 4 &times; 4
  35 pixel image</title>
  36
  37           <formalpara>
  38             <title>Byte Order.</title>
  39             <para>Each cell is one byte.
  40                 <informaltable frame="none">
  41                 <tgroup cols="5" align="center">
  42                   <colspec align="left" colwidth="2*" />
  43                   <tbody valign="top">
  44                     <row>
  45                       <entry>start&nbsp;+&nbsp;0:</entry>
  46                       <entry>Y'<subscript>00</subscript></entry>
  47                       <entry>Y'<subscript>01</subscript></entry>
  48                       <entry>Y'<subscript>02</subscript></entry>
  49                       <entry>Y'<subscript>03</subscript></entry>
  50                     </row>
  51                     <row>
  52                       <entry>start&nbsp;+&nbsp;4:</entry>
  53                       <entry>Y'<subscript>10</subscript></entry>
  54                       <entry>Y'<subscript>11</subscript></entry>
  55                       <entry>Y'<subscript>12</subscript></entry>
  56                       <entry>Y'<subscript>13</subscript></entry>
  57                     </row>
  58                     <row>
  59                       <entry>start&nbsp;+&nbsp;8:</entry>
  60                       <entry>Y'<subscript>20</subscript></entry>
  61                       <entry>Y'<subscript>21</subscript></entry>
  62                       <entry>Y'<subscript>22</subscript></entry>
  63                       <entry>Y'<subscript>23</subscript></entry>
  64                     </row>
  65                     <row>
  66                       <entry>start&nbsp;+&nbsp;12:</entry>
  67                       <entry>Y'<subscript>30</subscript></entry>
  68                       <entry>Y'<subscript>31</subscript></entry>
  69                       <entry>Y'<subscript>32</subscript></entry>
  70                       <entry>Y'<subscript>33</subscript></entry>
  71                     </row>
  72                     <row>
  73                       <entry>start&nbsp;+&nbsp;16:</entry>
  74                       <entry>Cb<subscript>00</subscript></entry>
  75                       <entry>Cr<subscript>00</subscript></entry>
  76                       <entry>Cb<subscript>01</subscript></entry>
  77                       <entry>Cr<subscript>01</subscript></entry>
  78                     </row>
  79                     <row>
  80                       <entry>start&nbsp;+&nbsp;20:</entry>
  81                       <entry>Cb<subscript>10</subscript></entry>
  82                       <entry>Cr<subscript>10</subscript></entry>
  83                       <entry>Cb<subscript>11</subscript></entry>
  84                       <entry>Cr<subscript>11</subscript></entry>
  85                     </row>
  86                   </tbody>
  87                 </tgroup>
  88                 </informaltable>
  89               </para>
  90           </formalpara>
  91
  92           <formalpara>
  93             <title>Color Sample Location.</title>
  94             <para>
  95                 <informaltable frame="none">
  96                 <tgroup cols="7" align="center">
  97                   <tbody valign="top">
  98                     <row>
  99                       <entry></entry>
 100                       <entry>0</entry><entry></entry><entry>1</entry><entry></entry>
 101                       <entry>2</entry><entry></entry><entry>3</entry>
 102                     </row>
 103                     <row>
 104                       <entry>0</entry>
 105                       <entry>Y</entry><entry></entry><entry>Y</entry><entry></entry>
 106                       <entry>Y</entry><entry></entry><entry>Y</entry>
 107                     </row>
 108                     <row>
 109                       <entry></entry>
 110                       <entry></entry><entry>C</entry><entry></entry><entry></entry>
 111                       <entry></entry><entry>C</entry><entry></entry>
 112                     </row>
 113                     <row>
 114                       <entry>1</entry>
 115                       <entry>Y</entry><entry></entry><entry>Y</entry><entry></entry>
 116                       <entry>Y</entry><entry></entry><entry>Y</entry>
 117                     </row>
 118                     <row>
 119                       <entry></entry>
 120                     </row>
 121                     <row>
 122                       <entry>2</entry>
 123                       <entry>Y</entry><entry></entry><entry>Y</entry><entry></entry>
 124                       <entry>Y</entry><entry></entry><entry>Y</entry>
 125                     </row>
 126                     <row>
 127                       <entry></entry>
 128                       <entry></entry><entry>C</entry><entry></entry><entry></entry>
 129                       <entry></entry><entry>C</entry><entry></entry>
 130                     </row>
 131                     <row>
 132                       <entry>3</entry>
 133                       <entry>Y</entry><entry></entry><entry>Y</entry><entry></entry>
 134                       <entry>Y</entry><entry></entry><entry>Y</entry>
 135                     </row>
 136                   </tbody>
 137                 </tgroup>
 138                 </informaltable>
 139               </para>
 140           </formalpara>
 141         </example>
 142       </refsect1>
 143     </refentry>
 144
 145   <!--
 146 Local Variables:
 147 mode: sgml
 148 sgml-parent-document: "pixfmt.sgml"
 149 indent-tabs-mode: nil
 150 End:
 151   -->