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<title>14.9 imghdr -- Determine the type of an image</title>
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<H1><A NAME="SECTION0016900000000000000000">
14.9 <tt class="module">imghdr</tt> --
         Determine the type of an image</A>
</H1>

<P>
<A NAME="module-imghdr"></A>

<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><table cellpadding="0" cellspacing="0"><tr valign="baseline">
  <td><nobr><b><tt id='l2h-4762' xml:id='l2h-4762' class="function">what</tt></b>(</nobr></td>
  <td><var>filename</var><big>[</big><var>, h</var><big>]</big><var></var>)</td></tr></table></dt>
<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>
<div class="center"><table class="realtable">
  <thead>
    <tr>
      <th class="left"  >Value</th>
      <th class="left"  >Image format</th>
      </tr>
    </thead>
  <tbody>
    <tr><td class="left"   valign="baseline"><code>'rgb'</code></td>
        <td class="left"  >SGI ImgLib Files</td></tr>
    <tr><td class="left"   valign="baseline"><code>'gif'</code></td>
        <td class="left"  >GIF 87a and 89a Files</td></tr>
    <tr><td class="left"   valign="baseline"><code>'pbm'</code></td>
        <td class="left"  >Portable Bitmap Files</td></tr>
    <tr><td class="left"   valign="baseline"><code>'pgm'</code></td>
        <td class="left"  >Portable Graymap Files</td></tr>
    <tr><td class="left"   valign="baseline"><code>'ppm'</code></td>
        <td class="left"  >Portable Pixmap Files</td></tr>
    <tr><td class="left"   valign="baseline"><code>'tiff'</code></td>
        <td class="left"  >TIFF Files</td></tr>
    <tr><td class="left"   valign="baseline"><code>'rast'</code></td>
        <td class="left"  >Sun Raster Files</td></tr>
    <tr><td class="left"   valign="baseline"><code>'xbm'</code></td>
        <td class="left"  >X Bitmap Files</td></tr>
    <tr><td class="left"   valign="baseline"><code>'jpeg'</code></td>
        <td class="left"  >JPEG data in JFIF format</td></tr>
    <tr><td class="left"   valign="baseline"><code>'bmp'</code></td>
        <td class="left"  >BMP files</td></tr>
    <tr><td class="left"   valign="baseline"><code>'png'</code></td>
        <td class="left"  >Portable Network Graphics</td></tr></tbody>
</table></div>

<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><tt id='l2h-4763' xml:id='l2h-4763'>tests</tt></b></dt>
<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.
</dd></dl>

<P>
Example:

<P>
<div class="verbatim"><pre>
&gt;&gt;&gt; import imghdr
&gt;&gt;&gt; imghdr.what('/tmp/bass.gif')
'gif'
</pre></div>

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<span class="release-info">Release 2.4.2, documentation updated on 28 September 2005.</span>
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