optimization - How to compare all patches in two images in matlab? -


i have 2 images, let's a , b, sizes of need not same. a of dimension 255×255 , b of dimension 100×100. , dimension of patch 5×5 problem. need compare patches in a patches in b.

every patch overlapping neighboring patches. clear point, first patch in a a(1:5,1:5) (matlab notation). second patch a(2:6,1:5) , on, way till a(251:255,1:5) @ end of first row, , way a(251:255,251:255) last patch in a.

i have compare each of these patches against all patches in b. can see, there 251*251 patches in a , 96*96 patches in b. there lot comparisons made. , comparison euclidean distance, i.e, i'll take difference of 2 patches , sum squares. each patch comparison i'll scalar value result.

i implemented in matlab it's taking several minutes execute. please suggest me fastest way implement this. section bottlenecking entire project. code wrote given below. i'm not expert please forgive mistakes.

row = size(a,1);     col = size(a,2);  row2 = size(b,1);     col2 = size(b,2);  patch_long = zeros(5,5,(row2-4)*(col2-4));  idx = 1;  = 1:row2-4         j = 1:col2-4          patch_long(:,:,idx) = b(i:i+4,j:j+4);          idx = idx+1;      end  end  %// rearranged 'b' matrix 3d matrix each patch arranged  %// slide behind 1 one  parfor m = 1:row-4         n = 1:col-4          temp1 = bsxfun(@minus,(a(m:m+4,n:n+4)),patch_long);         temp2 = sum(sum(temp1.^2));          count = sum(temp2 <=threshold);          if count > 1              % xyzend         end      end end  %// count counts how many patches in 'b' close particular patch in 'a'.

you can use im2col extract patches

pa = im2col( a, [5 5], 'sliding' ); pb = im2bol( b, [5 5], 'sliding' ); % compute squared difference d = sum( bsxfun( @minus, permute( pa, [2 3 1] ), permute( pb, [3 2 1] ) ).^2, 3 );

by way, if not need distances , willing compromise approximation k nearest neighbors, might find patchmatch useful:
approximate k-nearest neighbors algorithm tailored image patches. efficient in terms of memory (space) usage , fast.


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