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[media] V4L: Add JPEG compression control class documentation
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Add DocBook entries for the JPEG control class.

Signed-off-by: Sylwester Nawrocki <s.nawrocki@samsung.com>
Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>
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Sylwester Nawrocki authored and Mauro Carvalho Chehab committed Feb 28, 2012
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Showing 5 changed files with 214 additions and 2 deletions.
20 changes: 20 additions & 0 deletions Documentation/DocBook/media/v4l/biblio.xml
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Expand Up @@ -128,6 +128,26 @@ url="http://www.ijg.org">http://www.ijg.org</ulink>)</corpauthor>
<subtitle>Version 1.02</subtitle>
</biblioentry>

<biblioentry id="itu-t81">
<abbrev>ITU-T.81</abbrev>
<authorgroup>
<corpauthor>International Telecommunication Union
(<ulink url="http://www.itu.int">http://www.itu.int</ulink>)</corpauthor>
</authorgroup>
<title>ITU-T Recommendation T.81
"Information Technology &mdash; Digital Compression and Coding of Continous-Tone
Still Images &mdash; Requirements and Guidelines"</title>
</biblioentry>

<biblioentry id="w3c-jpeg-jfif">
<abbrev>W3C JPEG JFIF</abbrev>
<authorgroup>
<corpauthor>The World Wide Web Consortium (<ulink
url="http://www.w3.org/Graphics/JPEG">http://www.w3.org</ulink>)</corpauthor>
</authorgroup>
<title>JPEG JFIF</title>
</biblioentry>

<biblioentry id="smpte12m">
<abbrev>SMPTE&nbsp;12M</abbrev>
<authorgroup>
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10 changes: 10 additions & 0 deletions Documentation/DocBook/media/v4l/compat.xml
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Expand Up @@ -2400,6 +2400,16 @@ details.</para>
</orderedlist>
</section>

<section>
<title>V4L2 in Linux 3.4</title>
<orderedlist>
<listitem>
<para>Added <link linkend="jpeg-controls">JPEG compression control
class</link>.</para>
</listitem>
</orderedlist>
</section>

<section id="other">
<title>Relation of V4L2 to other Linux multimedia APIs</title>

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161 changes: 161 additions & 0 deletions Documentation/DocBook/media/v4l/controls.xml
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Expand Up @@ -3436,6 +3436,167 @@ interface and may change in the future.</para>
</tbody>
</tgroup>
</table>
</section>

<section id="jpeg-controls">
<title>JPEG Control Reference</title>
<para>The JPEG class includes controls for common features of JPEG
encoders and decoders. Currently it includes features for codecs
implementing progressive baseline DCT compression process with
Huffman entrophy coding.</para>
<table pgwide="1" frame="none" id="jpeg-control-id">
<title>JPEG Control IDs</title>

<tgroup cols="4">
<colspec colname="c1" colwidth="1*" />
<colspec colname="c2" colwidth="6*" />
<colspec colname="c3" colwidth="2*" />
<colspec colname="c4" colwidth="6*" />
<spanspec namest="c1" nameend="c2" spanname="id" />
<spanspec namest="c2" nameend="c4" spanname="descr" />
<thead>
<row>
<entry spanname="id" align="left">ID</entry>
<entry align="left">Type</entry>
</row><row rowsep="1"><entry spanname="descr" align="left">Description</entry>
</row>
</thead>
<tbody valign="top">
<row><entry></entry></row>
<row>
<entry spanname="id"><constant>V4L2_CID_JPEG_CLASS</constant>&nbsp;</entry>
<entry>class</entry>
</row><row><entry spanname="descr">The JPEG class descriptor. Calling
&VIDIOC-QUERYCTRL; for this control will return a description of this
control class.

</entry>
</row>
<row>
<entry spanname="id"><constant>V4L2_CID_JPEG_CHROMA_SUBSAMPLING</constant></entry>
<entry>menu</entry>
</row>
<row id="jpeg-chroma-subsampling-control">
<entry spanname="descr">The chroma subsampling factors describe how
each component of an input image is sampled, in respect to maximum
sample rate in each spatial dimension. See <xref linkend="itu-t81"/>,
clause A.1.1. for more details. The <constant>
V4L2_CID_JPEG_CHROMA_SUBSAMPLING</constant> control determines how
Cb and Cr components are downsampled after coverting an input image
from RGB to Y'CbCr color space.
</entry>
</row>
<row>
<entrytbl spanname="descr" cols="2">
<tbody valign="top">
<row>
<entry><constant>V4L2_JPEG_CHROMA_SUBSAMPLING_444</constant>
</entry><entry>No chroma subsampling, each pixel has
Y, Cr and Cb values.</entry>
</row>
<row>
<entry><constant>V4L2_JPEG_CHROMA_SUBSAMPLING_422</constant>
</entry><entry>Horizontally subsample Cr, Cb components
by a factor of 2.</entry>
</row>
<row>
<entry><constant>V4L2_JPEG_CHROMA_SUBSAMPLING_420</constant>
</entry><entry>Subsample Cr, Cb components horizontally
and vertically by 2.</entry>
</row>
<row>
<entry><constant>V4L2_JPEG_CHROMA_SUBSAMPLING_411</constant>
</entry><entry>Horizontally subsample Cr, Cb components
by a factor of 4.</entry>
</row>
<row>
<entry><constant>V4L2_JPEG_CHROMA_SUBSAMPLING_410</constant>
</entry><entry>Subsample Cr, Cb components horizontally
by 4 and vertically by 2.</entry>
</row>
<row>
<entry><constant>V4L2_JPEG_CHROMA_SUBSAMPLING_GRAY</constant>
</entry><entry>Use only luminance component.</entry>
</row>
</tbody>
</entrytbl>
</row>
<row>
<entry spanname="id"><constant>V4L2_CID_JPEG_RESTART_INTERVAL</constant>
</entry><entry>integer</entry>
</row>
<row><entry spanname="descr">
The restart interval determines an interval of inserting RSTm
markers (m = 0..7). The purpose of these markers is to additionally
reinitialize the encoder process, in order to process blocks of
an image independently.
For the lossy compression processes the restart interval unit is
MCU (Minimum Coded Unit) and its value is contained in DRI
(Define Restart Interval) marker. If <constant>
V4L2_CID_JPEG_RESTART_INTERVAL</constant> control is set to 0,
DRI and RSTm markers will not be inserted.
</entry>
</row>
<row id="jpeg-quality-control">
<entry spanname="id"><constant>V4L2_CID_JPEG_COMPRESION_QUALITY</constant></entry>
<entry>integer</entry>
</row>
<row>
<entry spanname="descr">
<constant>V4L2_CID_JPEG_COMPRESION_QUALITY</constant> control
determines trade-off between image quality and size.
It provides simpler method for applications to control image quality,
without a need for direct reconfiguration of luminance and chrominance
quantization tables.

In cases where a driver uses quantization tables configured directly
by an application, using interfaces defined elsewhere, <constant>
V4L2_CID_JPEG_COMPRESION_QUALITY</constant> control should be set
by driver to 0.

<para>The value range of this control is driver-specific. Only
positive, non-zero values are meaningful. The recommended range
is 1 - 100, where larger values correspond to better image quality.
</para>
</entry>
</row>
<row id="jpeg-active-marker-control">
<entry spanname="id"><constant>V4L2_CID_JPEG_ACTIVE_MARKER</constant></entry>
<entry>bitmask</entry>
</row>
<row>
<entry spanname="descr">Specify which JPEG markers are included
in compressed stream. This control is valid only for encoders.
</entry>
</row>
<row>
<entrytbl spanname="descr" cols="2">
<tbody valign="top">
<row>
<entry><constant>V4L2_JPEG_ACTIVE_MARKER_APP0</constant></entry>
<entry>Application data segment APP<subscript>0</subscript>.</entry>
</row><row>
<entry><constant>V4L2_JPEG_ACTIVE_MARKER_APP1</constant></entry>
<entry>Application data segment APP<subscript>1</subscript>.</entry>
</row><row>
<entry><constant>V4L2_JPEG_ACTIVE_MARKER_COM</constant></entry>
<entry>Comment segment.</entry>
</row><row>
<entry><constant>V4L2_JPEG_ACTIVE_MARKER_DQT</constant></entry>
<entry>Quantization tables segment.</entry>
</row><row>
<entry><constant>V4L2_JPEG_ACTIVE_MARKER_DHT</constant></entry>
<entry>Huffman tables segment.</entry>
</row>
</tbody>
</entrytbl>
</row>
<row><entry></entry></row>
</tbody>
</tgroup>
</table>
<para>For more details about JPEG specification, refer
to <xref linkend="itu-t81"/>, <xref linkend="jfif"/>,
<xref linkend="w3c-jpeg-jfif"/>.</para>
</section>
</section>
9 changes: 9 additions & 0 deletions Documentation/DocBook/media/v4l/v4l2.xml
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Expand Up @@ -127,6 +127,15 @@ structs, ioctls) must be noted in more detail in the history chapter
(compat.xml), along with the possible impact on existing drivers and
applications. -->

<revision>
<revnumber>3.4</revnumber>
<date>2012-01-25</date>
<authorinitials>sn</authorinitials>
<revremark>Added <link linkend="jpeg-controls">JPEG compression
control class.</link>
</revremark>
</revision>

<revision>
<revnumber>3.3</revnumber>
<date>2012-01-11</date>
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16 changes: 14 additions & 2 deletions Documentation/DocBook/media/v4l/vidioc-g-jpegcomp.xml
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Expand Up @@ -57,6 +57,11 @@
<refsect1>
<title>Description</title>

<para>These ioctls are <emphasis role="bold">deprecated</emphasis>.
New drivers and applications should use <link linkend="jpeg-controls">
JPEG class controls</link> for image quality and JPEG markers control.
</para>

<para>[to do]</para>

<para>Ronald Bultje elaborates:</para>
Expand Down Expand Up @@ -86,7 +91,10 @@ to add them.</para>
<row>
<entry>int</entry>
<entry><structfield>quality</structfield></entry>
<entry></entry>
<entry>Deprecated. If <link linkend="jpeg-quality-control"><constant>
V4L2_CID_JPEG_IMAGE_QUALITY</constant></link> control is exposed by
a driver applications should use it instead and ignore this field.
</entry>
</row>
<row>
<entry>int</entry>
Expand Down Expand Up @@ -116,7 +124,11 @@ to add them.</para>
<row>
<entry>__u32</entry>
<entry><structfield>jpeg_markers</structfield></entry>
<entry>See <xref linkend="jpeg-markers" />.</entry>
<entry>See <xref linkend="jpeg-markers"/>. Deprecated.
If <link linkend="jpeg-active-marker-control"><constant>
V4L2_CID_JPEG_ACTIVE_MARKER</constant></link> control
is exposed by a driver applications should use it instead
and ignore this field.</entry>
</row>
</tbody>
</tgroup>
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