GIMP Version: 2.8.16
Operating System: Windows
GIMP Experience: Basic Level

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I use an external software to find duplicated images.
I was wondering whether it has been produced a filter in Gimp able to compare two images and detect the percentage of similarities.
Any idea?

Is this what your looking for, How can I tell exactly what changed between two images?

It may come in handy?

Elsamuko Difference Layer Script

https://sites.google.com/site/elsamuko/gimp/difference

To determine the percentage I use an external software - XnView (only connection through Shelout)

thanks Odin, thanks Marero.
Hopefully someone may come out with a script which can be called like:
percentage = pdb.((script_fu)or(python_fu))_similarity (imageA, imageB)
with a return value of 0-100
spes ultima dea

IIRC there is a function like this ImageMagick. but I wonder how/why you would use it in a Gimp filter...

Logistically - how would one define "difference"?

- Would scaled versions of the same image be 100% the same or 100% different?
- Should the comparison be done pixel by pixel or some averaging?
- What colour space should the comparison happen in - RGB, CYM(K), HSV, HSL, LAB, etc....
- Does alpha/transparency count when comparing differences?
- What does a value of 50 mean - 50% of the pixels have any difference, 100% of the pixels are different by 50%, or something else?

-Rob A>

interesting technical aspects, RobA.
I don't know how "specialized" software (like "Awesome Duplicate Photo Finder") do the comparison.
IMO:
- images should be scaled equally (at least in one dimension) before comparing
- comparison should be able to identify as "almost equal" (80%?) an image compared with its copy a bit blurred
- same for transparency: comparison should be performed after transparency has been removed from both

but these are only my ideas....

let's see other opinions on these aspects
edit: maybe those who know and make use both of Gimp and ImageMagick can see how ImageMagick performs...

You can also have a look at the OpenCV library for python.

Here's the Imagemagick page about doing image comparisons: http://www.imagemagick.org/script/compare.php

Reverse engineering some Python I wrote to examine images captured from a bird nestbox camera:



Which gave me a 0->100 percentage measure of the difference and I deleted anything below a threshold as being insufficiently different.

Kevin

any specific reference? I'm a bit "dispersed" when looking at OpenCV.

something "portable" into Gimp, Kevin?

I stumbled upon python code to compare two images by jsbueno at Stack Overflow.
For a quick demo: Run the attached python script from the command line on the included images (not a Gimp plug-in). It requires Python Imaging Library (PIL)
I think ImageMacgick compare is the best option.

thanks Odin, still hoping to have sooner or later a Gimp filter.

Have you tried Gimp Compare images script yet?

I didn't, Odin.
Done now.
First tests not very...impressive: got always a third image fully white.
Also: a result being an image (should the filter work and show the differences) is not what I'm looking for: I'm looking for a simple percentage: similarity is 75%
"similarity = compare_images (imageA, imageB)"
Thanks anyhow, Odin, for your support

So here's a suggestion for you to code up...

Both images as layers
Set the mode of the top layer to "Difference"
New layer from Visible (gimp-layer-new-from-visible)
With New layer active, look at the histogram (gimp-histogram)
Divide the Mean value by 2.55 to get a percentage (You may want to consider the means of all 4 channels)

Kevin

Thanks Kevin.
I will do it.
Just for curiosity: is it what ImageMagick does?

Have a look at ImageMagick: -segment (segment the colors of an image)

Faster: desaturate, and pixellize the image to its own size (ie, make it one big pixel). The grey level will be a measure of the difference.