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<p class="navigation-index">[<a href="#usage">Example Usage</a> • <a href="#options">Option Summary</a>]</p>
<p>Use the <kbd>compare</kbd> program to mathematically and visually annotate the difference between an image and its reconstruction. See <a href="../www/command-line-processing.html">Command Line Processing</a> for advice on how to structure your <kbd>compare</kbd> command or see below for example usages of the command.</p>
<div style="margin: auto;">
<h2><a name="usage"></a>Example Usage</h2>
</div>
<p>We list a few examples of the <kbd>compare</kbd> command here to illustrate its usefulness and ease of use. To get started, lets compare an image to one thats been sharpened:</p>
<pre class="text">
convert rose.jpg -sharpen 0x1 reconstruct.jpg
compare rose.jpg reconstruct.jpg difference.png
</pre>
<p class="image">
<a href="../images/rose.jpg"><img src="../images/rose.jpg" width="70" height="46" align="middle" alt="rose" /></a>
<a href="../images/reconstruct.jpg"><img src="../images/reconstruct.jpg" width="70" height="46" align="middle" alt="rose" /></a>
<img src="../images/right.gif" width="20" height="20" align="middle" alt="==>" />
<a href="../images/difference.png"><img src="../images/difference.png" width="70" height="46" align="middle" alt="rose" /></a>
</p>
<p>The red areas of the difference image show which pixels were affected by the image sharpening, whereas, white is areas that were untouched by the sharpening process</p>
<p>In addition to the visual interpretation of the difference in an image and its reconstruction, we report a mathematical measure of the difference :</p>
<pre class="text">
compare -metric PSNR rose.jpg reconstruct.jpg difference.png
29.5615 dB
</pre>
<p>You can find additional examples of using <kbd>compare</kbd> in <a href="http://www-106.ibm.com/developerworks/library/l-graf/?ca=dnt-428" target="864266436">Graphics from the Command Line</a>. Further discussion is available in <a href="http://www-106.ibm.com/developerworks/library/l-graf2/?ca=dgr-lnxw15GraphicsLine" target="1901976299">More Graphics from the Command Line</a> and <a href="http://www.imagemagick.org/Usage/" target="320904222">Examples of ImageMagick Usage</a>.</p>
<div style="margin: auto;">
<h2><a name="options"></a>Option Summary</h2>
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<p>The <kbd>compare</kbd> command recognizes these options. Click on an option to get more details about how that option works.</p>
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<th align="left">Option</th>
<th align="left">Description</th>
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<tr>
<td valign="top"><a href="../www/command-line-options.html#alpha" target="magick-options">-alpha</a></td>
<td valign="top">activate, deactivate, reset, or set the alpha channel</td>
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<tr>
<td valign="top"><a href="../www/command-line-options.html#authenticate" target="magick-options">-authenticate <em class="option">value</em></a></td>
<td valign="top">decrypt image with this password</td>
</tr>
<tr>
<td valign="top"><a href="../www/command-line-options.html#channel" target="magick-options">-channel <em class="option">type</em></a></td>
<td valign="top">apply option to select image channels</td>
</tr>
<tr>
<td valign="top"><a href="../www/command-line-options.html#colorspace" target="magick-options">-colorspace <em class="option">type</em></a></td>
<td valign="top">set image colorspace</td>
<
/tr>
<tr>
<td valign="top"><a href="../www/command-line-options.html#decipher" target="magick-options">-decipher <em class="option">filename</em></a></td>
<td valign="top">convert cipher pixels to plain</td>
</tr>
<tr>
<td valign="top"><a href="../www/command-line-options.html#debug" target="magick-options">-debug <em class="option">events</em></a></td>
<td valign="top">display copious debugging information</td>
</tr>
<tr>
<td valign="top"><a href="../www/command-line-options.html#define" target="magick-options">-define <em class="option">format:option</em></a></td>
<td valign="top">define one or more image format options</td>
</tr>
<tr>
<td valign="top"><a href="../www/command-line-options.html#density" target="magick-options">-density <em class="option">geometry</em></a></td>
<td valign="top">horizontal and vertical density of the image</td>
</tr>
<tr>
<td valign="top"><a href="../www/command-line-options.html#depth" target="magick-options">-depth <em class="option">value</em></a></td>
<td valign="top">image depth</td>
</tr>
<tr>
<td valign="top"><a href="../www/command-line-options.html#encipher" target="magick-options">-encipher <em class="option">filename</em></a></td>
<td valign="top">convert plain pixels to cipher pixels</td>
</tr>
<tr>
<td valign="top"><a href="../www/command-line-options.html#extract" target="magick-options">-extract <em class="option">geometry</em></a></td>
<td valign="top">extract area from image</td>
</tr>
<tr>
<td valign="top"><a href="../www/command-line-options.html#fuzz" target="magick-options">-fuzz <em class="option">distance</em></a></td>
<td valign="top">colors within this distance are considered equal</td>
</tr>
<tr>
<tr>
<td valign="top"><a href="../www/command-line-options.html#help" target="magick-options">-help</a></td>
<td valign="top">print program options</td>
</tr>
<tr>
<td valign="top"><a href="../www/command-line-options.html#identify" target="magick-options">-identify</a></td>
<td valign="top">identify the format and characteristics of the image</td>
</tr>
<tr>
<td valign="top"><a href="../www/command-line-options.html#interlace" target="magick-options">-interlace <em class="option">type</em></a></td>
<td valign="top">type of image interlacing scheme</td>
</tr>
<tr>
<td valign="top"><a href="../www/command-line-options.html#limit" target="magick-options">-limit <em class="option">type value</em></a></td>
<td valign="top">pixel cache resource limit</td>
</tr>
<tr>
<td valign="top"><a href="../www/command-line-options.html#log" target="magick-options">-log <em class="option">format</em></a></td>
<td valign="top">format of debugging information</td>
</tr>
<tr>
<td valign="top"><a href="../www/command-line-options.html#metric" target="magick-options">-metric <em class="option">type</em></a></td>
<td valign="top">measure differences between images with this metric</td>
</tr>
<tr>
<td valign="top"><a href="../www/command-line-options.html#profile" target="magick-options">-profile <em class="option">filename</em></a></td>
<td valign="top">add, delete, or apply an image profile</td>
</tr>
<tr>
<td valign="top"><a href="../www/command-line-options.html#quality" target="magick-options">-quality <em class="option">value</em></a></td>
<td valign="top">JPEG/MIFF/PNG compression level</td>
</tr>
<tr>
<td valign="top"><a href="../www/command-line-options.html#quantize" target="magick-options">-quantize <em class="option">colorspace</em></a></td>
<td valign="top">reduce image colors in this colorspace</td>
</tr>
<tr>
<td valign="top"><a href="../www/command-line-options.html#quiet" target="magick-options">-quiet</a></td>
<td valign="top">suppress all warning messages</td>
</tr>
<tr>
<td valign="top"><a href="../www/command-line-options.html#sampling-factor" target="magick-options">-sampling-factor <em class="option">geometry</em></a></td>
<td valign="top">horizontal and vertical sampling factor</td>
</tr>
<tr>
<td valign="top"><a href="../www/command-line-options.html#seed" target="magick-options">-seed <em class="option">value</em></a></td>
<td valign="top">seed a new sequence of pseudo-random numbers</td>
</tr>
<tr>
<td valign="top"><a href="../www/command-line-options.html#set" target="magick-options">-set <em class="option">attribute value</em></a></td>
<td valign="top">set an image attribute</td>
</tr>
<tr>
<td valign="top"><a href="../www/command-line-options.html#size" target="magick-options">-size <em class="option">geometry</em></a></td>
<td valign="top">width and height of image</td>
</tr>
<tr>
<td valign="top"><a href="../www/command-line-options.html#transparent-color" target="magick-options">-transparent-color <em class="option">color</em></a></td>
<td valign="top">transparent color</td>
</tr>
<tr>
<td valign="top"><a href="../www/command-line-options.html#verbose" target="magick-options">-verbose</a></td>
<td valign="top">print detailed information about the image</td>
</tr>
<tr>
<td valign="top"><a href="../www/command-line-options.html#version" target="magick-options">-version</a></td>
<td valign="top">print version information</td>
</tr>
<tr>
<td valign="top"><a href="../www/command-line-options.html#virtual-pixel" target="magick-options">-virtual-pixel <em class="option">method</em></a></td>
<td valign="top">access method for pixels outside the boundaries of the image</td>
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