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<H1><A NAME="SECTION0016900000000000000000">
14.9 <tt class="module">imghdr</tt> --
Determine the type of an image</A>
</H1>
<P>
<P>
The <tt class="module">imghdr</tt> module determines the type of image contained in a
file or byte stream.
<P>
The <tt class="module">imghdr</tt> module defines the following function:
<P>
<dl><dt><b><a name='l2h-2933'><tt class='function'>what</tt></a></b> (<var>filename</var><big>[</big><var>, h</var><big>]</big>)
<dd>
Tests the image data contained in the file named by <var>filename</var>,
and returns a string describing the image type. If optional <var>h</var>
is provided, the <var>filename</var> is ignored and <var>h</var> is assumed to
contain the byte stream to test.
</dl>
<P>
The following image types are recognized, as listed below with the
return value from <tt class="function">what()</tt>:
<P>
<table border align="center" style="border-collapse: collapse">
<thead>
<tr class="tableheader">
<th align="left"><b>Value</b> </th>
<th align="left"><b>Image format</b> </th>
</thead>
<tbody valign='baseline'>
<tr><td align="left" valign="baseline"><code>'rgb'</code></td>
<td align="left">SGI ImgLib Files</td>
<tr><td align="left" valign="baseline"><code>'gif'</code></td>
<td align="left">GIF 87a and 89a Files</td>
<tr><td align="left" valign="baseline"><code>'pbm'</code></td>
<td align="left">Portable Bitmap Files</td>
<tr><td align="left" valign="baseline"><code>'pgm'</code></td>
<td align="left">Portable Graymap Files</td>
<tr><td align="left" valign="baseline"><code>'ppm'</code></td>
<td align="left">Portable Pixmap Files</td>
<tr><td align="left" valign="baseline"><code>'tiff'</code></td>
<td align="left">TIFF Files</td>
<tr><td align="left" valign="baseline"><code>'rast'</code></td>
<td align="left">Sun Raster Files</td>
<tr><td align="left" valign="baseline"><code>'xbm'</code></td>
<td align="left">X Bitmap Files</td>
<tr><td align="left" valign="baseline"><code>'jpeg'</code></td>
<td align="left">JPEG data in JFIF format</td>
<tr><td align="left" valign="baseline"><code>'bmp'</code></td>
<td align="left">BMP files</td>
<tr><td align="left" valign="baseline"><code>'png'</code></td>
<td align="left">Portable Network Graphics</td></tbody>
</table>
<P>
You can extend the list of file types <tt class="module">imghdr</tt> can recognize by
appending to this variable:
<P>
<dl><dt><b><a name='l2h-2934'><tt>tests</tt></a></b>
<dd>
A list of functions performing the individual tests. Each function
takes two arguments: the byte-stream and an open file-like object.
When <tt class="function">what()</tt> is called with a byte-stream, the file-like
object will be <code>None</code>.
<P>
The test function should return a string describing the image type if
the test succeeded, or <code>None</code> if it failed.
</dl>
<P>
Example:
<P>
<dl><dd><pre class="verbatim">
>>> import imghdr
>>> imghdr.what('/tmp/bass.gif')
'gif'
</pre></dl>
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