problem in for loop

       for i = 1:2:n
         filename = strcat('I:\testing\8y\',num2str(i),'.jpg');
        I = imread(filename);
        I1 = rgb2gray(I);
         mat1(:,:,i)= I1;
        end
        for j = 1:1:i-1
        r1 =  mat1(:,:,j);
        r2 = mat1(:,:,j+1);
        c = corr2(r1,r2);
        mat2(j) = c;
        end

When I run this code I got absurd results having zeros at alternate positions. most probably the reason is absence of even images in mat1(:,:,i) since i takes only odd values. Then I made a change in r2 as r2 = mat1(:,:,j+2), but it produced an error as "index exceeds matrix dimension". What should be the solution of this problem, so that r1 and r2 read odd values of i in a regular manner.

thanks
Navneet nayan

Answer 1

[Jan]

Would it help to use

for j = 1:1:i-2   % Instead of ...-1
  ...
  r2 = mat1(:,:,j+2);

?

[NAVNEET NAYAN]

yeah...it's working now... thanks a lot Simon

[Guillaume]

The for loop should be

for j = 1:2:i-2   %step of 2!

for the code to make sense.

Answer 2

[Guillaume]

What is the point of having a matrix mat1 twice the size it needs to be, storing lots of useless 0. Why not decouple the iterating of the files from the filling of the matrix:

imageindices = 1:2:n;
for i = 1:numel(imageindices)
  filepath = fullfile('I:\testing\8y', sprintf('%d.jpg', imageindices(i))); %prefer fullfile to strcat for building paths
  mat1(:, :, i) = rgb2gray(imread(filepath));
end

The second loop is then trivial:

for i = 1:size(mat1, 3)-1
   mat2(i) = corr(mat1(:, :, i), mat1(:, :, i+1));
end