Fred's ImageMagick Scripts
My scripts are available free of charge for non-commercial use. If you redistribute or incorporate any of these scripts into other free applications, you may use my scripts by simply referencing my name and this web page: Fred Weinhaus and http://www.fmwconcepts.com/imagemagick/index.html For use of my scripts in commercial use or non-free applications, please contact me for
licensing arrangements. Usage, whether stated in script or not, is also subject to the ImageMagick license, which can be found at: http://www.imagemagick.org/script/license.php |
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Computes the normalized cross correlation similarity metric between two equal dimensioned images |
last modified: May 02, 2012
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USAGE: similar [-m mode] infile1 infile2 -m ..... mode ..... colorspace mode; g (for grayscale) or rgb; default=g PURPOSE: To compute the normalized cross correlation similarity metric between two equal dimensioned images. DESCRIPTION: SIMILAR computes the normalized cross correlation similarity metric between two equal dimensioned images. The normalized cross correlation metric measures how similar two images are, not how different they are. The range of ncc metric values is between 0 (dissimilar) and 1 (similar). If mode=g, then the two images will be converted to grayscale. If mode=rgb, then the two images first will be converted to colorspace=rgb. Next, the ncc similarity metric will be computed for each channel. Finally, they will be combined into an rms value. NOTE: this metric does not work for constant color channels as it produces an ncc metric = 0/0 for that channel. Thus it is not advised to run the script with either image having a totally opaque or totally transparent alpha channel that is enabled. ARGUMENTS: -m mode ... MODE for colorspace to use when applying the normalized cross correlation metric on the two images. If mode=g, then the two image will be converted to grayscale. If mode=rgb, then the ncc similarity metric will be computed for each channel and then combined as its rms value. Default=g For reference on the normalized cross correlation metric, see http://en.wikipedia.org/wiki/Cross-correlation#Normalized_cross-correlation CAVEAT: No guarantee that this script will work on all platforms, nor that trapping of inconsistent parameters is complete and foolproof. Use At Your Own Risk. |
(provided by user kinder, see http://www.imagemagick.org/discourse-server/viewtopic.php?f=1&t=15264)
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Image 1 |
Image 2 |
NCC Metric |
NCC Metric |
1a.jpg |
1b.jpg |
0.879866 |
0.876972 |
2a.jpg |
2b.jpg |
0.30973 |
0.331926 |
3a.jpg |
3b.jpg |
0.240242 |
0.240434 |
4a.jpg |
4b.jpg |
0.807486 |
0.806117 |
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1a.jpg |
1a.jpg |
1.0042 |
1.00107 |
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1a.jpg |
convert 1a.jpg -negate 1an.jpg |
0 |
0 |
convert cyclops.png -fuzz 10% |
convert cyclops.png -fuzz 3% |
0.977871 |
0.987846 |
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What the script does is as follows (for any channel):
This is equivalent to the following IM commands for the case of mode=g:
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