ImageMagick: Command-line Tools: Compare

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
  28.31

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.

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Option	Description
-alpha	activate, deactivate, reset, or set the alpha channel
-authenticate value	decrypt image with this password
-channel type	apply option to select image channels
-colorspace type	set image colorspace
-decipher filename	convert cipher pixels to plain
-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
-encipher filename	convert plain pixels to cipher pixels
-extract geometry	extract area from image
-fuzz distance	colors within this distance are considered equal
-help	print program options
-highlight-color color	highlight pixel differences with this color
-identify	identify the format and characteristics of the image
-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
-quantize colorspace	reduce image colors in this colorspace
-quiet	suppress all warning messages
-regard-warnings	pay attention to warning messages.
-respect-parenthesis	settings remain in effect until parenthesis boundary.
-sampling-factor geometry	horizontal and vertical sampling factor
-seed value	seed a new sequence of pseudo-random numbers
-set attribute value	set an image attribute
-size geometry	width and height of image
-transparent-color color	transparent color
-verbose	print detailed information about the image
-version	print version information
-virtual-pixel method	access method for pixels outside the boundaries of the image