compareing 2 images with different dimension

[lkawcab]

Good Day,

I have a script that takes screen cap of some of our pages. Then it compares the screen cap from a previous capture. Here is the command I am ussing

compare image1.png image2.png -compose src result.png
Now I am getting a message : compare.im6: image widths or heights differ

Is there a way to still compare the images if the have different widths and heights.

Take Note, I am comparing 1000s of images and I am not sure as to which one might have changed in width or height.

Thank you in advance.
Law

[snibgo]

See the recent thread viewtopic.php?f=1&t=26882

[fmw42]

compare can be run with two image that are different sizes using -subimage-search option. That will try to move the smaller image around the larger one and tell you the location for the best match. Once you have that match, you can crop the larger image so that it has the same size as the smaller image. Then you can compare the two same sized images to get a visual of the differences. Actually the subimage-search mode produces two output images. The first shows where the to images match on the larger image size. The second, I believe, gives you the difference image for that location with differences marked in red. But you may want to use -compose difference on the two same sized images to get a better non-binary coloration showing the differences as described in the reference from snibgo above. Or see the -highlight-color and the -lowlight-color for colorizing the compare results.

See
http://www.imagemagick.org/script/compare.php
http://www.imagemagick.org/Usage/compare/
viewtopic.php?f=1&t=14613&p=51076&hilit ... ric#p51076 (but now needs -subimage-search added)
http://www.imagemagick.org/Usage/compose/#difference

It might help us understand your problem, if you upload a pair of images that you want to compare to some place like dropbox.com and put the URL here. Also it is always a good idea to provide your IM version and platform.

[lkawcab]

Here 2 sample images i have
https://www.dropbox.com/s/j8nxfzoty47ll ... 1.png?dl=0
https://www.dropbox.com/s/3dv3ny1tnb72d ... 2.png?dl=0

What is the proper syntax to use -subimage-search?

I am on a linux mint machine.
ImageMagick version is 6.7.7

Cheers,
Law

[fmw42]

Code: Select all

compare -metric rmse -subimage-search image1.png image2.png cmp1.png cmp2.png

3332.79 (0.0508551) @ 13,0

The larger image must be listed first.

Look at cmp2.png. It is the size of the larger image1.png and shows the best match with differences in red.

The values returned are

rmse difference in 0 to 65535 graylevel range and (rmse difference in range 0 to 1) and the offset coordinates of the small image relative to the top left corner of the large image. The rmse values show a 5.08551% error or difference.


If you just want the match score and don't care about the difference image, then just do

Code: Select all

compare -metric rmse -subimage-search image1.png image2.png null:

EDIT:

The proper syntax is

Code: Select all

compare -metric rmse -subimage-search image1.png image2.png cmp.png

compare uses only one output file, but makes two resulting images, cmp-0.png and cmp-1.png. The difference image is cmp-0.png and cmp-1.png is the match score image showing the rmse value (negated) for each shift position.

[lkawcab]

I ran the command compare -metric rmse -subimage-search image2.png image1.png cmp2.png cmp1.png (because image2 is bigger for my case.) I got the results below:

compare.im6: unable to open image `cmp2.png': No such file or directory @ error/blob.c/OpenBlob/2638.
compare.im6: unable to open file `cmp2.png' @ error/png.c/ReadPNGImage/3667.
compare.im6: image size differs `image2.png' @ error/compare.c/SimilarityMetricImage/1794.

[fmw42]

My mistake, the command needs only one output, but makes two from the same name with -0 and -1 appended. So try

Code: Select all

compare -metric rmse -subimage-search image2.png image1.png cmp.png

and look at cmp-0.png


I will edit my command above.

P.S. If you are using the same images as posted, then image1 is larger than image2! The larger image must be listed first.

[lkawcab]

Thank you! It works like a charm!

For clarification, will this work when both images have the same size?

[fmw42]

Yes it appears to do so. But if for some reason it does not, then for same size images, leave off the -subimage-search.