lør, 29 12 2007 kl. 14:06 -0600, skrev Daniel Elliott:
Hello,
I tried contacting the author, but the email address is no longer
functional. I have not done my homework before asking the question...
The imtranslate function takes the absolute value of the image as it
is brought out of FFT-space. Is this because of some property of FFT
where it can potentially flip the sign of a pixel?
I am using this method to permute images that may have negative
values. Does anyone know why the absolute value is used here?
I haven't written (or even used) imtranslate so I don't know the
details. I assume that FFT sometimes returns complex values, so an abs()
is needed. Depending on your problem, I suggest you either
1) Separate the signs from the data and transform each separately.
Something like:
S = sign(im);
im = abs(im);
St = imtranslate(S, ...)
imt = imtranslate(im, ...)
T = St.*imt;
2) Use the more general 'imperspectivewarp'. You can just apply an
affine transformation matrix like
T = [eye(2), [Tx; Ty]];
where Tx and Ty are your translations.
Hope that helps,
Søren
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