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I have a rather difficult image processing image. I would like to rank order a set of images I have by their sharpness. The issue is the images themselves are not of the exact same thing. Usual methods I see rely that the underlying blur-free image is identical, but in my case this is not true. Some methods I have tried:

integration of a band of spatial frequencies (i.e., 2D Fourier transform of image) average of gradient wavelet transform eigenvalue decomposition

None of these have worked so far. They all work, in principle, if the image underneath is identical. Does anyone have some ideas how they would approach this problem?

I have a rather difficult image processing image. I would like to rank order a set of images I have by their sharpness. The issue is the images themselves are not of the exact same thing. Usual methods I see rely that the underlying blur-free image is identical, but in my case this is not true. 

Some methods I have tried:

• integration of a band of spatial frequencies (i.e., 2D Fourier transform of image)
• average of gradient
• wavelet transform
• eigenvalue decomposition

None of these have worked so far. They all work, in principle, if the image underneath is identical. Does anyone have some ideas how they would approach this problem?