I was going through this question for the explanation of affine transform for a quadrilateral (in the link).
However, I want to perform affine transform for perspective correction of a n-sided polygon, for any n (obviously > 3). Can anyone please explain me how to do it or suggest a OpenCV [or something similar] implementation so that I can implement it?
Thanks in advance.
http://stackoverflow.com/questions/10667834/trying-to-understand-the-affine-transform
If I understand you correctly, you should study projective transformations. They are capable of representing the "perspective correction" you mentioned. If you have such a transformation, you apply it to all the points, no matter how many...
See e.g.: http://homepages.inf.ed.ac.uk/rbf/CVonline/LOCAL_COPIES/BEARDSLEY/node3.html
If you need something like the pinhole camera model, then see e.g.:
http://www.ics.uci.edu/~majumder/vispercep/cameracalib.pdf
Y = PX, where P is your perspective 3x4 matrix [R|t] with R=roation and t=translation; X is the matrix whose columns are the points of your source polygon, and Y is the matrix whose columns are the destination points of your polygon, in homogeneous coordinates, of course, i.e. [x,y,w]', gaining the 2D coordinates as [x/w, y/w,1]
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