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<H1><A NAME="SECTION00201200000000000000000">
18.12 <tt class="module">jpeg</tt> --
Read and write JPEG files</A>
</H1>
<P>
<p class='availability'>Availability: <span
class='platform'>IRIX</span>.</p>
<P>
The module <tt class="module">jpeg</tt> provides access to the jpeg compressor and
decompressor written by the Independent JPEG Group
(IJG). JPEG is a standard for
compressing pictures; it is defined in ISO 10918. For details on JPEG
or the Independent JPEG Group software refer to the JPEG standard or
the documentation provided with the software.
<P>
A portable interface to JPEG image files is available with the Python
Imaging Library (PIL) by Fredrik Lundh. Information on PIL is
available at <a class="url" href="javascript:if(confirm('http://www.pythonware.com/products/pil/ \n\nThis file was not retrieved by Teleport Pro, because it is addressed on a domain or path outside the boundaries set for its Starting Address. \n\nDo you want to open it from the server?'))window.location='http://www.pythonware.com/products/pil/'" tppabs="http://www.pythonware.com/products/pil/">http://www.pythonware.com/products/pil/ <img src="offsite.gif" tppabs="http://www.python.org/doc/current/icons/offsite.gif"
border='0' class='offsitelink' height='15' width='17' alt='[off-site link]'
></a>.
<P>
The <tt class="module">jpeg</tt> module defines an exception and some functions.
<P>
<dl><dt><b><a name='l2h-3256'><tt class='exception'>error</tt></a></b>
<dd>
Exception raised by <tt class="function">compress()</tt> and <tt class="function">decompress()</tt>
in case of errors.
</dl>
<P>
<dl><dt><b><a name='l2h-3257'><tt class='function'>compress</tt></a></b> (<var>data, w, h, b</var>)
<dd>
Treat data as a pixmap of width <var>w</var> and height <var>h</var>, with
<var>b</var> bytes per pixel. The data is in SGI GL order, so the first
pixel is in the lower-left corner. This means that <tt class="function">gl.lrectread()</tt>
return data can immediately be passed to <tt class="function">compress()</tt>.
Currently only 1 byte and 4 byte pixels are allowed, the former being
treated as greyscale and the latter as RGB color.
<tt class="function">compress()</tt> returns a string that contains the compressed
picture, in JFIF format.
</dl>
<P>
<dl><dt><b><a name='l2h-3258'><tt class='function'>decompress</tt></a></b> (<var>data</var>)
<dd>
Data is a string containing a picture in JFIF format. It
returns a tuple <code>(<var>data</var>, <var>width</var>, <var>height</var>,
<var>bytesperpixel</var>)</code>. Again, the data is suitable to pass to
<tt class="function">gl.lrectwrite()</tt>.
</dl>
<P>
<dl><dt><b><a name='l2h-3259'><tt class='function'>setoption</tt></a></b> (<var>name, value</var>)
<dd>
Set various options. Subsequent <tt class="function">compress()</tt> and
<tt class="function">decompress()</tt> calls will use these options. The following
options are available:
<P>
<table border align="center" style="border-collapse: collapse">
<thead>
<tr class="tableheader">
<th align="left"><b>Option</b> </th>
<th align="left"><b>Effect</b> </th>
</thead>
<tbody valign='baseline'>
<tr><td align="left" valign="baseline"><code>'forcegray'</code></td>
<td align="left">Force output to be grayscale, even if input is RGB.</td>
<tr><td align="left" valign="baseline"><code>'quality'</code></td>
<td align="left">Set the quality of the compressed image to a value between
<code>0</code> and <code>100</code> (default is <code>75</code>). This only affects
compression.</td>
<tr><td align="left" valign="baseline"><code>'optimize'</code></td>
<td align="left">Perform Huffman table optimization. Takes longer, but results in
smaller compressed image. This only affects compression.</td>
<tr><td align="left" valign="baseline"><code>'smooth'</code></td>
<td align="left">Perform inter-block smoothing on uncompressed image. Only useful
for low-quality images. This only affects decompression.</td></tbody>
</table>
</dl>
<P>
<div class='seealso'>
<p class='heading'><b>See Also:</b></p>
<div class="seetext"><p><i>JPEG Still Image Data Compression Standard</i>, by
Pennebaker and Mitchell, is the canonical reference for the JPEG
image format.</div>
<P>
<div class="seetext"><p>The ISO standard for JPEG is also published as ITU T.81.
This is available in PDF form at
<a class="url" href="javascript:if(confirm('http://www.w3.org/Graphics/JPEG/itu-t81.pdf \n\nThis file was not retrieved by Teleport Pro, because it is addressed on a domain or path outside the boundaries set for its Starting Address. \n\nDo you want to open it from the server?'))window.location='http://www.w3.org/Graphics/JPEG/itu-t81.pdf'" tppabs="http://www.w3.org/Graphics/JPEG/itu-t81.pdf">http://www.w3.org/Graphics/JPEG/itu-t81.pdf <img src="offsite.gif" tppabs="http://www.python.org/doc/current/icons/offsite.gif"
border='0' class='offsitelink' height='15' width='17' alt='[off-site link]'
></a>.</div>
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