--- bakoguz <> wrote:> I have a problem of for loops. > I saw the messages about them but it did not help > me. > I want to filter my matrix(actually an image) by a > filter > and I want to convolve(2D) my filter with my image. > If I use > for loops, I need two of them, but the execution is > too slow. > > Can you suggest something about it ? > > Thank you... > > burak > Example Problem : > > % 3x3 mean filter > mask = [ 1/9 1/9 1/9 ; 1/9 1/9 1/9 ; 1/9 1/9 1/9] ; > > [row_mask, col_mask] = size(mask) ; > > [row_im , col_im , rgb_ ] = size(image) ; > > image = im2double(image,'indexed'); > > result_image = image ; > > for k = 1 : (row_im + 1 - row_mask), > for m = 1 : (col_im + 1 - col_mask), > > part_of_im=image(k:row_mask+k-1,m:col_mask+m-1); > temp_matrix = times(part_of_im , mask) ; > sum_temp = round( sum(sum(temp_matrix)) ) ; > temp_index_row = k-1 +(row_mask+1)/2 ; > temp_index_col = m-1 +(col_mask+1)/2 ; > result_image(temp_index_row , > temp_index_col) = sum_temp ; > > end; > end; > Hi, If I followed correctly your example you just want to put the average of 9 surrounding pixels at each pixel. The following transformation matrix does it for square samples: B=diag(ones(N-1),1); % N is the height (and width) T=eye(N)+B+B'; % Transformation matrix Then apply it: Result=T*A*T/9; % A is the original matrix *End* You can try to generalize it to non-square matrices or to divide your matrix to square blocks. Joe BSTEX - Equation viewer for Matlab http://www.geocities.com/bstex2001 > > __________________________________________________ |

# Re: For Loop Execution

Started by ●December 9, 2001