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This is a simple image classification problem. I want to categorize jigsaw puzzle images to difficulty levels (e.g, easy, medium, hard).

I want to develop an simple algorithm for this classification, which is based on factors like large solid colored areas, repeating patterns on the image (more details). Such classification can be seen in following website. example 1

I want to automate this without much human interventions. Is this possible and whats the best way to approach it. (not worried about performance, simple is good, does not need huge accuracy)

EDIT

I was able to generate the magnitude and phase plots of the 2d FFT. However, I am not clear how to come up with a classification by looking at magnitude plot. Any ideas.

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  • $\begingroup$ I think you do not have a well-defined, calculable metric. $\endgroup$ – Emre Jan 24 '16 at 19:15
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    $\begingroup$ The problem here is that you asked a very specific question (large solid color areas) and then came up with a completely different topic (classification of jigsaw puzzles). What you should do before any coding: Think very carefully about what parameters make a jigsaw puzzle hard or easy. Are there correlations between them? And if you came up with, lets say 3 - 5 parameters, then state them here and also give us the reason why you think that those are good parameters. Then it is easier (for us and you) to come up with an idea for an algorithm to quantify those parameters from images. $\endgroup$ – M529 Mar 24 '16 at 12:22
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Perhaps you could classify the difficulty by assuming that higher spatial frequency implies higher difficulty. Make sure all the images are the same size, do a 2D FFT, and look at the spatial bandwidth in x and y dimensions, would be my suggestion.

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  • $\begingroup$ Thank you very much for your answer. I am not an expert in this area. Can you give me some helpful links or general algorithm I could implement and try out? $\endgroup$ – user2943193 Sep 26 '15 at 3:37
  • $\begingroup$ I kind of gave you the algorithm already... do you know what an FFT is? If not, I would start there. $\endgroup$ – CMDoolittle Sep 26 '15 at 3:46
  • $\begingroup$ I was able to generate the magnitude and phase plots of the 2d FFT. However, I am not clear how to come up with a classification by looking at magnitude plot. Any ideas. Lets say Easy i.telegraph.co.uk/multimedia/archive/02431/… Medium difficult mangomaniafl.net/wpcontent/uploads/2014/06/…, Hard is mytechquest.com/blog/wp-content/uploads/2010/10/… $\endgroup$ – user2943193 Sep 27 '15 at 11:46
  • $\begingroup$ The problem with the pure spatial frequency approach is that it would classify solid colors and very busy noise (of the type in the bottom image of the linked examples) at opposite ends of the easy/hard space when they should be equally hard. I think difficulty is probably a function spatial frequency relative to the piece size with easy being somewhere in the middle. I'm not stating that with great clarity, but the metric isn't terribly clear either... $\endgroup$ – Omegaman Mar 24 '16 at 19:39

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