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  <title>ImageMagick: Command-line Tools: Compare</title>
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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>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="706478276">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="1335285656">More Graphics from the Command Line</a> and <a href="http://www.cit.gu.edu.au/~anthony/graphics/imagick6" target="1010841363">Examples of ImageMagick Usage</a>.</p>

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  <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>
  </tr>

<tr>
    <td><a href="../www/command-line-options.html#authenticate" target="magick-options">-authenticate <em class="option">value</em></a></td>
    <td>decrypt image with this password</td>
  </tr>

<tr>
    <td><a href="../www/command-line-options.html#channel" target="magick-options">-channel <em class="option">type</em></a></td>
    <td>apply option to select image channels</td>
  </tr>

<tr>
    <td><a href="../www/command-line-options.html#colorspace" target="magick-options">-colorspace <em class="option">type</em></a></td>
    <td>alternate image colorspace</td>
  </tr>

<tr>
    <td><a href="../www/command-line-options.html#debug" target="magick-options">-debug <em class="option">events</em></a></td>
    <td>display copious debugging information</td>
  </tr>

<tr>
    <td><a href="../www/command-line-options.html#define" target="magick-options">-define <em class="option">format:option</em></a></td>
    <td>define one or more image format options</td>
  </tr>

<tr>
    <td><a href="../www/command-line-options.html#density" target="magick-options">-density <em class="option">geometry</em></a></td>
    <td>horizontal and vertical density of the image</td>
  </tr>

<tr>
    <td><a href="../www/command-line-options.html#depth" target="magick-options">-depth <em class="option">value</em></a></td>
    <td>image depth</td>
  </tr>

<tr>
    <td><a href="../www/command-line-options.html#extract" target="magick-options">-extract <em class="option">geometry</em></a></td>
    <td>extract area from image</td>
  </tr>

<tr>
    <td><a href="../www/command-line-options.html#help" target="magick-options">-help</a></td>
    <td>print program options</td>
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<tr>
    <td><a href="../www/command-line-options.html#identify" target="magick-options">&ndash;identify</a></td>
    <td>identify the format and characteristics of the image</td>
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<tr>
    <td><a href="../www/command-line-options.html#interlace" target="magick-options">-interlace <em class="option">type</em></a></td>
    <td>type of image interlacing scheme</td>
  </tr>

<tr>
    <td><a href="../www/command-line-options.html#limit" target="magick-options">-limit <em class="option">type value</em></a></td>
    <td>pixel cache resource limit</td>
  </tr>

<tr>
    <td><a href="../www/command-line-options.html#log" target="magick-options">-log <em class="option">format</em></a></td>
    <td>format of debugging information</td>
  </tr>

<tr>
    <td><a href="../www/command-line-options.html#metric" target="magick-options">-metric <em class="option">type</em></a></td>
    <td>measure differences between images with this metric</td>
  </tr>

<tr>
    <td><a href="../www/command-line-options.html#profile" target="magick-options">-profile <em class="option">filename</em></a></td>
    <td>add, delete, or apply an image profile</td>
  </tr>

<tr>
    <td><a href="../www/command-line-options.html#quality" target="magick-options">-quality <em class="option">value</em></a></td>
    <td>JPEG/MIFF/PNG compression level</td>
  </tr>

<tr>
    <td><a href="../www/command-line-options.html#quiet" target="magick-options">-quiet</a></td>
    <td>suppress all error or warning messages</td>
  </tr>

<tr>
    <td><a href="../www/command-line-options.html#sampling-factor" target="magick-options">-sampling-factor <em class="option">geometry</em></a></td>
    <td>horizontal and vertical sampling factor</td>
  </tr>

<tr>
    <td><a href="../www/command-line-options.html#set" target="magick-options">-set <em class="option">attribute value</em></a></td>
    <td>set an image attribute</td>
  </tr>

<tr>
    <td><a href="../www/command-line-options.html#size" target="magick-options">-size <em class="option">geometry</em></a></td>
    <td>width and height of image</td>
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<tr>
    <td><a href="../www/command-line-options.html#verbose" target="magick-options">-verbose</a></td>
    <td>print detailed information about the image</td>
  </tr>

<tr>
    <td><a href="../www/command-line-options.html#version" target="magick-options">-version</a></td>
    <td>print version information</td>
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<tr>
    <td><a href="../www/command-line-options.html#virtual-pixel" target="magick-options">-virtual-pixel <em class="option">method</em></a></td>
    <td>access method for pixels outside the boundaries of the image</td>
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