Documentation/DocBook/v4l/pixfmt-yuv420.xml

   1     <refentry>
   2       <refmeta>
   3         <refentrytitle>V4L2_PIX_FMT_YVU420 ('YV12'), V4L2_PIX_FMT_YUV420 ('YU12')</refentrytitle>
   4         &manvol;
   5      </refmeta>
   6       <refnamediv>
   7         <refname id="V4L2-PIX-FMT-YVU420"><constant>V4L2_PIX_FMT_YVU420</constant></refname>
   8         <refname id="V4L2-PIX-FMT-YUV420"><constant>V4L2_PIX_FMT_YUV420</constant></refname>
   9         <refpurpose>Planar formats with &frac12; horizontal and
  10 vertical chroma resolution, also known as YUV 4:2:0</refpurpose>
  11       </refnamediv>
  12       <refsect1>
  13         <title>Description</title>
  14
  15         <para>These are planar formats, as opposed to a packed format.
  16 The three components are separated into three sub- images or planes.
  17 The Y plane is first. The Y plane has one byte per pixel. For
  18 <constant>V4L2_PIX_FMT_YVU420</constant>, the Cr plane immediately
  19 follows the Y plane in memory. The Cr plane is half the width and half
  20 the height of the Y plane (and of the image). Each Cr belongs to four
  21 pixels, a two-by-two square of the image. For example,
  22 Cr<subscript>0</subscript> belongs to Y'<subscript>00</subscript>,
  23 Y'<subscript>01</subscript>, Y'<subscript>10</subscript>, and
  24 Y'<subscript>11</subscript>. Following the Cr plane is the Cb plane,
  25 just like the Cr plane. <constant>V4L2_PIX_FMT_YUV420</constant> is
  26 the same except the Cb plane comes first, then the Cr plane.</para>
  27
  28         <para>If the Y plane has pad bytes after each row, then the Cr
  29 and Cb planes have half as many pad bytes after their rows. In other
  30 words, two Cx rows (including padding) is exactly as long as one Y row
  31 (including padding).</para>
  32
  33         <example>
  34           <title><constant>V4L2_PIX_FMT_YVU420</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>Cr<subscript>00</subscript></entry>
  75                       <entry>Cr<subscript>01</subscript></entry>
  76                     </row>
  77                     <row>
  78                       <entry>start&nbsp;+&nbsp;18:</entry>
  79                       <entry>Cr<subscript>10</subscript></entry>
  80                       <entry>Cr<subscript>11</subscript></entry>
  81                     </row>
  82                     <row>
  83                       <entry>start&nbsp;+&nbsp;20:</entry>
  84                       <entry>Cb<subscript>00</subscript></entry>
  85                       <entry>Cb<subscript>01</subscript></entry>
  86                     </row>
  87                     <row>
  88                       <entry>start&nbsp;+&nbsp;22:</entry>
  89                       <entry>Cb<subscript>10</subscript></entry>
  90                       <entry>Cb<subscript>11</subscript></entry>
  91                     </row>
  92                   </tbody>
  93                 </tgroup>
  94                 </informaltable>
  95               </para>
  96           </formalpara>
  97
  98           <formalpara>
  99             <title>Color Sample Location.</title>
 100             <para>
 101                 <informaltable frame="none">
 102                 <tgroup cols="7" align="center">
 103                   <tbody valign="top">
 104                     <row>
 105                       <entry></entry>
 106                       <entry>0</entry><entry></entry><entry>1</entry><entry></entry>
 107                       <entry>2</entry><entry></entry><entry>3</entry>
 108                     </row>
 109                     <row>
 110                       <entry>0</entry>
 111                       <entry>Y</entry><entry></entry><entry>Y</entry><entry></entry>
 112                       <entry>Y</entry><entry></entry><entry>Y</entry>
 113                     </row>
 114                     <row>
 115                       <entry></entry>
 116                       <entry></entry><entry>C</entry><entry></entry><entry></entry>
 117                       <entry></entry><entry>C</entry><entry></entry>
 118                     </row>
 119                     <row>
 120                       <entry>1</entry>
 121                       <entry>Y</entry><entry></entry><entry>Y</entry><entry></entry>
 122                       <entry>Y</entry><entry></entry><entry>Y</entry>
 123                     </row>
 124                     <row>
 125                       <entry></entry>
 126                     </row>
 127                     <row>
 128                       <entry>2</entry>
 129                       <entry>Y</entry><entry></entry><entry>Y</entry><entry></entry>
 130                       <entry>Y</entry><entry></entry><entry>Y</entry>
 131                     </row>
 132                     <row>
 133                       <entry></entry>
 134                       <entry></entry><entry>C</entry><entry></entry><entry></entry>
 135                       <entry></entry><entry>C</entry><entry></entry>
 136                     </row>
 137                     <row>
 138                       <entry>3</entry>
 139                       <entry>Y</entry><entry></entry><entry>Y</entry><entry></entry>
 140                       <entry>Y</entry><entry></entry><entry>Y</entry>
 141                     </row>
 142                   </tbody>
 143                 </tgroup>
 144                 </informaltable>
 145               </para>
 146           </formalpara>
 147         </example>
 148       </refsect1>
 149     </refentry>
 150
 151   <!--
 152 Local Variables:
 153 mode: sgml
 154 sgml-parent-document: "pixfmt.sgml"
 155 indent-tabs-mode: nil
 156 End:
 157   -->