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<div class="section" id="module-jpeg">
<h1>38.12. <tt class="xref docutils literal"><span class="pre">jpeg</span></tt> — Read and write JPEG files<a class="headerlink" href="#module-jpeg" title="Permalink to this headline">¶</a></h1>
<p><em>Platforms: </em>IRIX</p>
<p class="deprecated">
<span class="versionmodified">Deprecated since version 2.6: </span>The <tt class="xref docutils literal"><span class="pre">jpeg</span></tt> module has been deprecated for removal in Python 3.0.</p>
<p id="index-407">The module <tt class="xref docutils literal"><span class="pre">jpeg</span></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>
<p id="index-408">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="reference external" href="http://www.pythonware.com/products/pil/">http://www.pythonware.com/products/pil/</a>.</p>
<p>The <tt class="xref docutils literal"><span class="pre">jpeg</span></tt> module defines an exception and some functions.</p>
<dl class="exception">
<dt id="jpeg.error">
<em class="property">exception </em><tt class="descclassname">jpeg.</tt><tt class="descname">error</tt><a class="headerlink" href="#jpeg.error" title="Permalink to this definition">¶</a></dt>
<dd>Exception raised by <a title="jpeg.compress" class="reference internal" href="#jpeg.compress"><tt class="xref docutils literal"><span class="pre">compress()</span></tt></a> and <a title="jpeg.decompress" class="reference internal" href="#jpeg.decompress"><tt class="xref docutils literal"><span class="pre">decompress()</span></tt></a> in case of errors.</dd></dl>
<dl class="function">
<dt id="jpeg.compress">
<tt class="descclassname">jpeg.</tt><tt class="descname">compress</tt><big>(</big><em>data</em>, <em>w</em>, <em>h</em>, <em>b</em><big>)</big><a class="headerlink" href="#jpeg.compress" title="Permalink to this definition">¶</a></dt>
<dd><p id="index-409">Treat data as a pixmap of width <em>w</em> and height <em>h</em>, with <em>b</em> 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="xref docutils literal"><span class="pre">gl.lrectread()</span></tt> return data can immediately be passed to
<a title="jpeg.compress" class="reference internal" href="#jpeg.compress"><tt class="xref docutils literal"><span class="pre">compress()</span></tt></a>. Currently only 1 byte and 4 byte pixels are allowed, the
former being treated as greyscale and the latter as RGB color. <a title="jpeg.compress" class="reference internal" href="#jpeg.compress"><tt class="xref docutils literal"><span class="pre">compress()</span></tt></a>
returns a string that contains the compressed picture, in JFIF format.</p>
</dd></dl>
<dl class="function">
<dt id="jpeg.decompress">
<tt class="descclassname">jpeg.</tt><tt class="descname">decompress</tt><big>(</big><em>data</em><big>)</big><a class="headerlink" href="#jpeg.decompress" title="Permalink to this definition">¶</a></dt>
<dd><p id="index-410">Data is a string containing a picture in JFIF format. It returns a tuple
<tt class="docutils literal"><span class="pre">(data,</span> <span class="pre">width,</span> <span class="pre">height,</span> <span class="pre">bytesperpixel)</span></tt>. Again, the data is suitable to pass
to <tt class="xref docutils literal"><span class="pre">gl.lrectwrite()</span></tt>.</p>
</dd></dl>
<dl class="function">
<dt id="jpeg.setoption">
<tt class="descclassname">jpeg.</tt><tt class="descname">setoption</tt><big>(</big><em>name</em>, <em>value</em><big>)</big><a class="headerlink" href="#jpeg.setoption" title="Permalink to this definition">¶</a></dt>
<dd><p>Set various options. Subsequent <a title="jpeg.compress" class="reference internal" href="#jpeg.compress"><tt class="xref docutils literal"><span class="pre">compress()</span></tt></a> and <a title="jpeg.decompress" class="reference internal" href="#jpeg.decompress"><tt class="xref docutils literal"><span class="pre">decompress()</span></tt></a> calls
will use these options. The following options are available:</p>
<table border="1" class="docutils">
<colgroup>
<col width="27%" />
<col width="73%" />
</colgroup>
<thead valign="bottom">
<tr><th class="head">Option</th>
<th class="head">Effect</th>
</tr>
</thead>
<tbody valign="top">
<tr><td><tt class="docutils literal"><span class="pre">'forcegray'</span></tt></td>
<td>Force output to be grayscale, even if input
is RGB.</td>
</tr>
<tr><td><tt class="docutils literal"><span class="pre">'quality'</span></tt></td>
<td>Set the quality of the compressed image to
a value between <tt class="docutils literal"><span class="pre">0</span></tt> and <tt class="docutils literal"><span class="pre">100</span></tt> (default
is <tt class="docutils literal"><span class="pre">75</span></tt>). This only affects compression.</td>
</tr>
<tr><td><tt class="docutils literal"><span class="pre">'optimize'</span></tt></td>
<td>Perform Huffman table optimization. Takes
longer, but results in smaller compressed
image. This only affects compression.</td>
</tr>
<tr><td><tt class="docutils literal"><span class="pre">'smooth'</span></tt></td>
<td>Perform inter-block smoothing on
uncompressed image. Only useful for low-
quality images. This only affects
decompression.</td>
</tr>
</tbody>
</table>
</dd></dl>
<div class="admonition-see-also admonition seealso">
<p class="first admonition-title">See also</p>
<dl class="last docutils">
<dt>JPEG Still Image Data Compression Standard</dt>
<dd>The canonical reference for the JPEG image format, by Pennebaker and Mitchell.</dd>
<dt><a class="reference external" href="http://www.w3.org/Graphics/JPEG/itu-t81.pdf">Information Technology - Digital Compression and Coding of Continuous-tone Still Images - Requirements and Guidelines</a></dt>
<dd>The ISO standard for JPEG is also published as ITU T.81. This is available
online in PDF form.</dd>
</dl>
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