Documentation/DocBook/media/v4l/pixfmt-yuv420m.xml

   1     <refentry>
   2       <refmeta>
   3         <refentrytitle>V4L2_PIX_FMT_YUV420M ('YM12'), V4L2_PIX_FMT_YVU420M ('YM21')</refentrytitle>
   4         &manvol;
   5       </refmeta>
   6       <refnamediv>
   7         <refname id="V4L2-PIX-FMT-YUV420M"><constant>V4L2_PIX_FMT_YUV420M</constant></refname>
   8         <refname id="V4L2-PIX-FMT-YVU420M"><constant>V4L2_PIX_FMT_YVU420M</constant></refname>
   9         <refpurpose>Variation of <constant>V4L2_PIX_FMT_YUV420</constant> and
  10           <constant>V4L2_PIX_FMT_YVU420</constant> with planes non contiguous
  11           in memory.</refpurpose>
  12       </refnamediv>
  13
  14       <refsect1>
  15         <title>Description</title>
  16
  17         <para>This is a multi-planar format, as opposed to a packed format.
  18 The three components are separated into three sub-images or planes.</para>
  19
  20         <para>The Y plane is first. The Y plane has one byte per pixel.
  21 For <constant>V4L2_PIX_FMT_YUV420M</constant> the Cb data
  22 constitutes the second plane which is half the width and half
  23 the height of the Y plane (and of the image). Each Cb belongs to four
  24 pixels, a two-by-two square of the image. For example,
  25 Cb<subscript>0</subscript> belongs to Y'<subscript>00</subscript>,
  26 Y'<subscript>01</subscript>, Y'<subscript>10</subscript>, and
  27 Y'<subscript>11</subscript>. The Cr data, just like the Cb plane, is
  28 in the third plane.</para>
  29
  30         <para><constant>V4L2_PIX_FMT_YVU420M</constant> is the same except
  31 the Cr data is stored in the second plane and the Cb data in the third plane.
  32 </para>
  33
  34         <para>If the Y plane has pad bytes after each row, then the Cb
  35 and Cr planes have half as many pad bytes after their rows. In other
  36 words, two Cx rows (including padding) is exactly as long as one Y row
  37 (including padding).</para>
  38
  39         <para><constant>V4L2_PIX_FMT_YUV420M</constant> and
  40 <constant>V4L2_PIX_FMT_YVU420M</constant> are intended to be
  41 used only in drivers and applications that support the multi-planar API,
  42 described in <xref linkend="planar-apis"/>. </para>
  43
  44         <example>
  45           <title><constant>V4L2_PIX_FMT_YUV420M</constant> 4 &times; 4
  46 pixel image</title>
  47
  48           <formalpara>
  49             <title>Byte Order.</title>
  50             <para>Each cell is one byte.
  51                 <informaltable frame="none">
  52                 <tgroup cols="5" align="center">
  53                   <colspec align="left" colwidth="2*" />
  54                   <tbody valign="top">
  55                     <row>
  56                       <entry>start0&nbsp;+&nbsp;0:</entry>
  57                       <entry>Y'<subscript>00</subscript></entry>
  58                       <entry>Y'<subscript>01</subscript></entry>
  59                       <entry>Y'<subscript>02</subscript></entry>
  60                       <entry>Y'<subscript>03</subscript></entry>
  61                     </row>
  62                     <row>
  63                       <entry>start0&nbsp;+&nbsp;4:</entry>
  64                       <entry>Y'<subscript>10</subscript></entry>
  65                       <entry>Y'<subscript>11</subscript></entry>
  66                       <entry>Y'<subscript>12</subscript></entry>
  67                       <entry>Y'<subscript>13</subscript></entry>
  68                     </row>
  69                     <row>
  70                       <entry>start0&nbsp;+&nbsp;8:</entry>
  71                       <entry>Y'<subscript>20</subscript></entry>
  72                       <entry>Y'<subscript>21</subscript></entry>
  73                       <entry>Y'<subscript>22</subscript></entry>
  74                       <entry>Y'<subscript>23</subscript></entry>
  75                     </row>
  76                     <row>
  77                       <entry>start0&nbsp;+&nbsp;12:</entry>
  78                       <entry>Y'<subscript>30</subscript></entry>
  79                       <entry>Y'<subscript>31</subscript></entry>
  80                       <entry>Y'<subscript>32</subscript></entry>
  81                       <entry>Y'<subscript>33</subscript></entry>
  82                     </row>
  83                     <row><entry></entry></row>
  84                     <row>
  85                       <entry>start1&nbsp;+&nbsp;0:</entry>
  86                       <entry>Cb<subscript>00</subscript></entry>
  87                       <entry>Cb<subscript>01</subscript></entry>
  88                     </row>
  89                     <row>
  90                       <entry>start1&nbsp;+&nbsp;2:</entry>
  91                       <entry>Cb<subscript>10</subscript></entry>
  92                       <entry>Cb<subscript>11</subscript></entry>
  93                     </row>
  94                     <row><entry></entry></row>
  95                     <row>
  96                       <entry>start2&nbsp;+&nbsp;0:</entry>
  97                       <entry>Cr<subscript>00</subscript></entry>
  98                       <entry>Cr<subscript>01</subscript></entry>
  99                     </row>
 100                     <row>
 101                       <entry>start2&nbsp;+&nbsp;2:</entry>
 102                       <entry>Cr<subscript>10</subscript></entry>
 103                       <entry>Cr<subscript>11</subscript></entry>
 104                     </row>
 105                   </tbody>
 106                 </tgroup>
 107                 </informaltable>
 108               </para>
 109           </formalpara>
 110
 111           <formalpara>
 112             <title>Color Sample Location.</title>
 113             <para>
 114                 <informaltable frame="none">
 115                 <tgroup cols="7" align="center">
 116                   <tbody valign="top">
 117                     <row>
 118                       <entry></entry>
 119                       <entry>0</entry><entry></entry><entry>1</entry><entry></entry>
 120                       <entry>2</entry><entry></entry><entry>3</entry>
 121                     </row>
 122                     <row>
 123                       <entry>0</entry>
 124                       <entry>Y</entry><entry></entry><entry>Y</entry><entry></entry>
 125                       <entry>Y</entry><entry></entry><entry>Y</entry>
 126                     </row>
 127                     <row>
 128                       <entry></entry>
 129                       <entry></entry><entry>C</entry><entry></entry><entry></entry>
 130                       <entry></entry><entry>C</entry><entry></entry>
 131                     </row>
 132                     <row>
 133                       <entry>1</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                     </row>
 140                     <row>
 141                       <entry>2</entry>
 142                       <entry>Y</entry><entry></entry><entry>Y</entry><entry></entry>
 143                       <entry>Y</entry><entry></entry><entry>Y</entry>
 144                     </row>
 145                     <row>
 146                       <entry></entry>
 147                       <entry></entry><entry>C</entry><entry></entry><entry></entry>
 148                       <entry></entry><entry>C</entry><entry></entry>
 149                     </row>
 150                     <row>
 151                       <entry>3</entry>
 152                       <entry>Y</entry><entry></entry><entry>Y</entry><entry></entry>
 153                       <entry>Y</entry><entry></entry><entry>Y</entry>
 154                     </row>
 155                   </tbody>
 156                 </tgroup>
 157                 </informaltable>
 158               </para>
 159           </formalpara>
 160         </example>
 161       </refsect1>
 162     </refentry>