<!DOCTYPE html> <html lang="en"> <head> <meta charset="utf-8" /> <meta name="viewport" content="width=device-width, initial-scale=1, shrink-to-fit=no" /> <title>Command-line Tools: Compare @ ImageMagick</title> <meta name="application-name" content="ImageMagick" /> <meta name="description" content="ImageMagick® is a software suite to create, edit, compose, or convert bitmap images. It can read and write images in a variety of formats (over 200) including PNG, JPEG, JPEG-2000, GIF, WebP, Postscript, PDF, and SVG. 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See <a href="command-line-processing.html">Command Line Processing</a> for advice on how to structure your <code>compare</code> command or see below for example usages of the command.</p> <h2 class="magick-post-title"><a class="anchor" id="usage"></a>Example Usage</h2> <p>We list a few examples of the <code>compare</code> 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="highlight"><code>convert rose.jpg -sharpen 0x1 reconstruct.jpg compare rose.jpg reconstruct.jpg difference.png compare -compose src rose.jpg reconstruct.jpg difference.png </code></pre> <ul> <a href="../images/rose.jpg"><img src="../images/rose.jpg" width="70" height="46" alt="rose" /></a> <a href="../images/reconstruct.jpg"><img src="../images/reconstruct.jpg" width="70" height="46" alt="rose" /></a> <img style="margin:13px 0;" src="../images/right.gif" width="20" height="20" alt="==>" /> <a href="../images/difference.png"><img src="../images/difference.png" width="70" height="46" alt="rose" /></a> </ul> <p>The red areas of the difference image emphasizes (highlight) pixels that are affected by the image sharpening, whereas white de-emphasizes (lowlight) pixels that are 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="highlight"><code>-> compare -verbose -metric mae rose.jpg reconstruct.jpg difference.png Image: rose.jpg Channel distortion: MAE red: 2282.91 (0.034835) green: 1853.99 (0.0282901) blue: 2008.67 (0.0306503) all: 1536.39 (0.0234439) </code></pre> <p>Or, if you just want the red channel distortion, use this command:</p> <pre class="highlight"><code>-> compare -channel red -metric PSNR rose.jpg reconstruct.jpg difference.png 19.63 </code></pre> <p>Or, if you just want the overall image distortion, use this command:</p> <pre class="highlight"><code>-> compare -metric PSNR rose.jpg reconstruct.jpg difference.png 28.31 </code></pre> <p>If the reconstructed image is a subimage of the image, the compare program returns the best match offset. In addition, it returns a similarity image such that an exact match location is completely white and if none of the pixels match, black, otherwise some gray level in-between:</p> <pre class="highlight"><code>-> compare -metric RMSE -subimage-search logo.png wizard.jpg similarity.gif 85.05 (0.00129778) @ 353,157 </code></pre> <p>You can find additional examples of using <code>compare</code> in <a href="http://www.ibm.com/developerworks/library/l-graf/?ca=dnt-428">Graphics from the Command Line</a>. Further discussion is available in <a href="http://www.ibm.com/developerworks/library/l-graf2/?ca=dgr-lnxw15GraphicsLine">More Graphics from the Command Line</a> and <a href="https://www.imagemagick.org/Usage/">Examples of ImageMagick Usage</a>.</p> <p>The compare program returns 2 on error otherwise 0 if the images are similar or 1 if they are dissimilar as defined by the metric and fuzz. The normalized cross correlation error metric is an exception. For this metric, 1 is interpreted as two identical images.</p> <h2 class="magick-post-title"><a class="anchor" id="options"></a>Option Summary</h2> <p>The <code>compare</code> command recognizes these options. Click on an option to get more details about how that option works.</p> <table class="table table-sm table-striped"> <tbody> <tr> <th align="left">Option</th> <th align="left">Description</th> </tr> <tr> <td><a href="command-line-options.html#alpha">-alpha</a></td> <td>on, activate, off, deactivate, set, opaque, copy", transparent, extract, background, or shape the alpha channel</td> </tr> <tr> <td><a href="command-line-options.html#authenticate">-authenticate <var>value</var></a></td> <td>decrypt image with this password</td> </tr> <tr> <td><a href="command-line-options.html#background">-background <var>color</var></a></td> <td>background color</td> </tr> <tr> <td><a href="command-line-options.html#brightness-contrast">-brightness-contrast <var>geometry</var></a></td> <td>improve brightness / contrast of the image</td> </tr> <tr> <td><a href="command-line-options.html#channel">-channel <var>type</var></a></td> <td>apply option to select image channels</td> </tr> <tr> <td><a href="command-line-options.html#colorspace">-colorspace <var>type</var></a></td> <td>set image colorspace</td> </tr> <tr> <td><a href="command-line-options.html#compose">-compose <var>operator</var></a></td> <td>set image composite operator</td> </tr> <tr> <td><a href="command-line-options.html#crop">-crop <var>geometry</var></a></td> <td>crop the image</td> </tr> <tr> <td><a href="command-line-options.html#decipher">-decipher <var>filename</var></a></td> <td>convert cipher pixels to plain</td> </tr> <tr> <td><a href="command-line-options.html#debug">-debug <var>events</var></a></td> <td>display copious debugging information</td> </tr> <tr> <td><a href="command-line-options.html#define">-define <var>format:option</var></a></td> <td>define one or more image format options</td> </tr> <tr> <td><a href="command-line-options.html#density">-density <var>geometry</var></a></td> <td>horizontal and vertical density of the image</td> </tr> <tr> <td><a href="command-line-options.html#depth">-depth <var>value</var></a></td> <td>image depth</td> </tr> <tr> <td><a href="command-line-options.html#dissimilarity-threshold">-dissimilarity-threshold <var>value</var></a></td> <td>maximum distortion for (sub)image match (default 0.2)</td> </tr> <tr> <td><a href="command-line-options.html#distort">-distort <var>type coefficients</var></a></td> <td>distort image</td> </tr> <tr> <td><a href="command-line-options.html#encipher">-encipher <var>filename</var></a></td> <td>convert plain pixels to cipher pixels</td> </tr> <tr> <td><a href="command-line-options.html#extract">-extract <var>geometry</var></a></td> <td>extract area from image</td> </tr> <tr> <td><a href="command-line-options.html#fuzz">-fuzz <var>distance</var></a></td> <td>colors within this distance are considered equal</td> </tr> <tr> <td><a href="command-line-options.html#gravity">-gravity <var>type</var></a></td> <td>horizontal and vertical text placement</td> </tr> <tr> <tr> <td><a href="command-line-options.html#help">-help</a></td> <td>print program options</td> </tr> <tr> <td><a href="command-line-options.html#highlight-color">-highlight-color <var>color</var></a></td> <td>emphasize pixel differences with this color</td> </tr> <tr> <td><a href="command-line-options.html#identify">-identify</a></td> <td>identify the format and characteristics of the image</td> </tr> <tr> <td><a href="command-line-options.html#interlace">-interlace <var>type</var></a></td> <td>type of image interlacing scheme</td> </tr> <tr> <td><a href="command-line-options.html#level">-level <var>value</var></a></td> <td>adjust the level of image contrast</td> </tr> <tr> <td><a href="command-line-options.html#limit">-limit <var>type value</var></a></td> <td>pixel cache resource limit</td> </tr> <tr> <td><a href="command-line-options.html#log">-log <var>format</var></a></td> <td>format of debugging information</td> </tr> <tr> <td><a href="command-line-options.html#lowlight-color">-lowlight-color <var>color</var></a></td> <td>de-emphasize pixel differences with this color</td> </tr> <tr> <td><a href="command-line-options.html#metric">-metric <var>type</var></a></td> <td>measure differences between images with this metric</td> </tr> <tr> <td><a href="command-line-options.html#negate">-negate</a></td> <td>replace each pixel with its complementary color </td> </tr> <tr> <td><a href="command-line-options.html#profile">-profile <var>filename</var></a></td> <td>add, delete, or apply an image profile</td> </tr> <tr> <td><a href="command-line-options.html#quality">-quality <var>value</var></a></td> <td>JPEG/MIFF/PNG compression level</td> </tr> <tr> <td><a href="command-line-options.html#quantize">-quantize <var>colorspace</var></a></td> <td>reduce image colors in this colorspace</td> </tr> <tr> <td><a href="command-line-options.html#quiet">-quiet</a></td> <td>suppress all warning messages</td> </tr> <tr> <td><a href="command-line-options.html#read-mask">-read-mask <var>filename</var></a></td> <td>associate a read mask with the image</td> </tr> <tr> <td><a href="command-line-options.html#regard-warnings">-regard-warnings</a></td> <td>pay attention to warning messages.</td> </tr> <tr> <td><a href="command-line-options.html#repage">-repage <var>geometry</var></a></td> <td>size and location of an image canvas</td> </tr> <tr> <td><a href="command-line-options.html#resize">-resize <var>geometry</var></a></td> <td>resize the image</td> </tr> <tr> <td><a href="command-line-options.html#respect-parentheses">-respect-parentheses</a></td> <td>settings remain in effect until parenthesis boundary.</td> </tr> <tr> <td><a href="command-line-options.html#rotate">-rotate <var>degrees</var></a></td> <td>apply Paeth rotation to the image</td> </tr> <tr> <td><a href="command-line-options.html#sampling-factor">-sampling-factor <var>geometry</var></a></td> <td>horizontal and vertical sampling factor</td> </tr> <tr> <td><a href="command-line-options.html#seed">-seed <var>value</var></a></td> <td>seed a new sequence of pseudo-random numbers</td> </tr> <tr> <td><a href="command-line-options.html#separate">-separate</a></td> <td>separate an image channel into a grayscale image</td> </tr> <tr> <td><a href="command-line-options.html#set">-set <var>attribute value</var></a></td> <td>set an image attribute</td> </tr> <tr> <td><a href="command-line-options.html#sigmoidal">-sigmoidal-contrast <var>geometry</var></a></td> <td>increase the contrast without saturating highlights or shadows</td> </tr> <tr> <td><a href="command-line-options.html#similarity-threshold">-similarity-threshold <var>value</var></a></td> <td>minimum distortion for (sub)image match (default 0.0)</td> </tr> <tr> <td><a href="command-line-options.html#size">-size <var>geometry</var></a></td> <td>width and height of image</td> </tr> <tr> <td><a href="command-line-options.html#subimage-search">-subimage-search</a></td> <td>search for subimage</td> </tr> <tr> <td><a href="command-line-options.html#synchronize">-synchronize</a></td> <td>synchronize image to storage device</td> </tr> <tr> <td><a href="command-line-options.html#taint">-taint</a></td> <td>mark the image as modified</td> </tr> <tr> <td><a href="command-line-options.html#transparent-color">-transparent-color <var>color</var></a></td> <td>transparent color</td> </tr> <tr> <td><a href="command-line-options.html#trim">-trim</a></td> <td>trim image edges</td> </tr> <tr> <td><a href="command-line-options.html#verbose">-verbose</a></td> <td>print detailed information about the image</td> </tr> <tr> <td><a href="command-line-options.html#version">-version</a></td> <td>print version information</td> </tr> <tr> <td><a href="command-line-options.html#virtual-pixel">-virtual-pixel <var>method</var></a></td> <td>access method for pixels outside the boundaries of the image</td> </tr> <tr> <td><a href="command-line-options.html#write-mask">-read-mask 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