| Re: similarity of two images, identifying overlapping regions [message #54976 is a reply to message #54931] |
Sun, 22 July 2007 00:07  |
Craig Markwardt
Messages: 1869
Registered: November 1996
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Senior Member |
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thomas.nehls@tu-berlin.de writes:
> Hi there,
>
>
> the case: There are two different images from X-Ray imagery showing
> both parts, but not exactly the same, of a soil sample. The two images
> were taken with different wavelengths L1 and L2, showing the
> distribution of different elements.
> The purpose is to calculate with these element distributions later.
...
> I thought about holding one of the images and moving the other before
> the first row by row, then column by column (like the doctors do it on
> the light screen with the photograps of our bones or brains :-)
You are talking about doing an image cross correlation, which can be
done quickly using an FFT. The trick to using the FFT will be to
zero-pad the images to at least double their original size.
Such an FFT can handle a shift but not a rotation or scale factor.
You also mention that the images may be distorted.
I believe that cartographers have to deal with this kind of situation
-- matching distorted images -- and I believe they solve it by
brute-force. Namely, picking and matching a good sample of control
points in both images, and spline-resampling one image to the grid of
the other.
Good luck!
Craig
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Craig B. Markwardt, Ph.D. EMAIL: craigmnet@REMOVEcow.physics.wisc.edu
Astrophysics, IDL, Finance, Derivatives | Remove "net" for better response
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