CODEWITHSUNDEEP
imagematlabpolar-coordinatescartesian
Marko
Marko

Reputation: 13

Matlab: Extract Image in polar representation from Cartesian

I m trying to compute an efficient way to transform an image in cartesian coordinates into a polar representation. I know some functions such as ImToPolar are doing it and it works perfectly but takes a considerable much time for big images, especially when they require to be processed back and forth.

Here´s my input image:

input image

and then I generate a polar mesh using a cartesian mesh centered at 0 and the function cart2pol(). Finally, I plot my image using mesh(theta, r, Input).

And here´s what I obtain:

output image

Its exactly the image I need and it´s the same as ImToPolar or maybe better.

Since MATLAB knows how to compute it, does anybody know how to extract a matrix in polar representation from this output? Or maybe a fast (like in fast fourier transform) way to compute a Polar transform (and inverse) on MATLAB?

Upvotes: 1

Views: 1189

Answers (1)

rahnema1
rahnema1

Reputation: 15867

pol2cart and meshgrid and interp2 are sufficient to create the result:

I=imread('https://i.sstatic.net/HYSyb.png');
[r, c,~] = size(I);
%rgb image can be converted to indexed image to prevent excessive copmutation for each color
[idx, mp] = rgb2ind(I,32);
% add offset to image coordinates
x = (1:c)-(c/2);
y = (1:r)-(r/2);
% create distination coordinates in polar form so value of image can be interpolated in those coordinates
% angle ranges from 0 to 2 * pi and radius assumed that ranges from 0 to 400
% linspace(0,2*pi, 200) leads to a stretched image try it!
[xp yp] = meshgrid(linspace(0,2*pi), linspace(0,400));
%translate coordinate from polar to image coordinates
[xx , yy] = pol2cart(xp,yp);
% interpolate pixel values for unknwon coordinates
out = interp2(x, y, idx, xx, yy);
% save the result to a file
imwrite(out, mp, 'result.png')

Upvotes: 0

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