Compare two images to check if they are the same

Question

Which is the efficient way to compare two images (Bitmaps), to check if they are the same or not?

I've tried to document me and I've read that I need to re-size both images to around 16x16px, but I don't get the expected result.

I've tried to compare the resized images using .Equals:

    If img1.Equals(img2) then 
        msgbox("are equals!")
    End if

I've seen AForge image library but I can't found any method inside to compare Images.

Is there way to do an efficient Image comparison using .NET classes or 3rd party libs without hardcode a pixel-per-pixel image comparer? If not, any example of a function to compare images?

Answer 1

You need to think carefully about your requirements and what equal means. If you are doing a direct pixel by pixel comparison, then you can find numerous .net image classes to help with this (I am not a .net expert but try here Image Comparison for find percentage of similarity between images )

Of course implementing a simple direct image difference is fairly easy. You could even allow for slight differences with difference < threshold, which the tutorial in the above SO answer discusses. Incidentally this answer also mentions SIFT, which I did not realize until after I had mentioned it. SIFT is a good tool depending on your requirements.

The SIFT 3rd party tool is a great way to compare images that can have slight variations, but you might have to make a system call as I am not sure if they provide a .net interface. The definitive website for SIFT implementation is: http://www.cs.ubc.ca/~lowe/keypoints/

I did find this on the internet: http://www.nowozin.net/sebastian/tu-berlin-2006/libsift/ which claims to be a c# implementation.