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Use ImageMagic to compare Images
Posted: 2014-06-30T06:24:24-07:00
by Levan
want to compare a source png file to a compressed file.
I am using imagemagick and this command:
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convert image1 image2 -compose Difference -composite \
-colorspace gray -format '%[fx:mean*100]' info:
But what I get is a very odd number. I am looking from a number from 0-100%.
When I compared two totally different images I still get a 8.37885.
So good people of Ask Ubuntu, can you provide me with a command that will measure the difference between files properly and give me a number from 0-100?
For example
Get
42.0838
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convert image1 image2 -compose Difference -composite -format '%[fx:mean*100]' info:
With this command I get:
57.2969
So it there something wrong with the command I use ?? If yes can you recommend alternative??
Thank you for your help.
Thank You
Re: Use ImageMagic to compare Images
Posted: 2014-06-30T10:13:10-07:00
by fmw42
On these two image with IM 6.8.9.4 Q16 Mac OSX I get
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convert 1.png 2.png -compose Difference -composite -colorspace gray -format '%[fx:mean*100]' info:
So that is 48.3854%, which is a reasonable value, since fx:mean returns values between 0 and 1. However, you are weighting the r,g,b values unequally by using -colorspace gray.
So you might use
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convert 1.png 2.png -compose Difference -composite -grayscale average -format '%[fx:mean*100]' info:
57.2969
What version of IM are you using?
Another way to compare these images is with compare
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compare -metric rmse 1.png 2.png null:
46321.8 (0.706825)
Take the second and multiply by 100, gives 70.6825% using the rmse metric
This is pretty much the same as doing
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convert 1.png 2.png -compose Difference -composite -grayscale rms -format '%[fx:mean*100]' info:
70.1065
see
http://www.imagemagick.org/Usage/compare/
http://www.imagemagick.org/script/compare.php
http://www.imagemagick.org/script/comma ... #grayscale
Re: Use ImageMagic to compare Images
Posted: 2014-07-01T07:35:40-07:00
by Levan
fmw42
Thank you very much for your reply, and I apologize for taking so long to write you back.
I am using: ImageMagick 6.7.7-10 2014-03-06 Q16 version
The information you provided is very helpful so thank you for that.
Again thank you, you have been tremendous help
Re: Use ImageMagic to compare Images
Posted: 2014-07-01T09:15:00-07:00
by fmw42
IM 6.7.7.10 is ancient and too old for the function -grayscale. You should upgrade IM if possible. Your IM is over 100 versions old.
Re: Use ImageMagic to compare Images
Posted: 2014-07-01T15:47:08-07:00
by Levan
fmw42 wrote:IM 6.7.7.10 is ancient and too old for the function -grayscale. You should upgrade IM if possible. Your IM is over 100 versions old.
Thank you very much for the information, I will make sure to compile the latest version.