ImageMagick: Command-line Tools: Compare
Author: ImageMagick Studio LLC
Description: ImageMagick (TM) is a free software suite to create, edit and compose bitmap images. It can read, convert and write images in a large variety of formats. Images can be cropped, colors can be changed, various effects can be applied, images can be rotated and combined, and text, lines, polygons, ellipses and Bézier curves can be added to images and stretched and rotated. ImageMagick is free software: it is delivered with full source code and can be freely used, copied, modified and distributed. Its license is compatible with the GPL. It runs on all major operating systems. Most of the functionality of ImageMagick can be used interactively from the command line; more often, however, the features are used from programs written in the programming languages Perl, C, C++, Python, PHP, Ruby or Java, for which ready-made ImageMagick interfaces (PerlMagick, Magick++, PythonMagick, MagickWand for PHP, RubyMagick, and JMagick) are available. This makes it possible to modify or create images automa [cell cut: 1159 characters, first 1000 kept]
Keywords: command-line, tools:, compare, ImageMagick, PerlMagick, Magick++, Image, Magick

Use the `compare` program to mathematically and visually annotate the difference between an image and its reconstruction. See Command Line Processing for advice on how to structure your `compare` command or see below for example usages of the command. ## Example Usage We list a few examples of the `compare` command here to illustrate its usefulness and ease of use. To get started, lets compare an image to one thats been sharpened:
      convert rose.jpg -sharpen 0x1 reconstruct.jpg
      compare rose.jpg reconstruct.jpg difference.png
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 In addition to the visual interpretation of the difference in an image and its reconstruction, we report a mathematical measure of the difference :
      compare -metric PSNR rose.jpg reconstruct.jpg difference.png
      29.5615 dB
You can find additional examples of using `compare` in Graphics from the Command Line. Further discussion is available in More Graphics from the Command Line and Examples of ImageMagick Usage. ## Option Summary The `compare` command recognizes these options. Click on an option to get more details about how that option works.
Option | Description
--- | ---
-authenticate value | decrypt image with this password
-channel type | apply option to select image channels
-colorspace type | alternate image colorspace
-debug events | display copious debugging information
-define format:option | define one or more image format options
-density geometry | horizontal and vertical density of the image
-depth value | image depth
-extract geometry | extract area from image
-help | print program options
-interlace type | type of image interlacing scheme
-limit type value | pixel cache resource limit
-log format | format of debugging information
-metric type | measure differences between images with this metric
-profile filename | add, delete, or apply an image profile
-quality value | JPEG/MIFF/PNG compression level
-quiet | suppress all error or warning messages
-sampling-factor geometry | horizontal and vertical sampling factor
-set attribute value | set an image attribute
-size geometry | width and height of image
-verbose | print detailed information about the image
-version | print version information
-virtual-pixel method | access method for pixels outside the boundaries of the image

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