How to instead the "for" loop?

Hello, I had a program which use for loop and if, but it take a long time, I want it faster.

How Can I instead of "for" and "if" so that it can make the program become faster?

Here is the program, Thanks

tic

clear all
close all

mov = mmreader('02.avi');

for i = 1: 7111   % number of the frame of the video

      frame1 = read(mov, i);

      if i == 750

         for a = 300 :2: 303;
              for b = 353 :2: 381;
                  for c = 301 :2: 303;
                      for d = 354 :2: 381;

                  frame1(a,b,:) = [0,0,0];
                  frame1(c,d,:) = [0,0,0];
                      end
                  end
              end
          end 

          for a = 300 :2: 303;
              for b = 354 :2: 381;
                  for c = 301 :2: 303;
                      for d = 353 :2: 381;

                  frame1(a,b,:) = [153,153,153];
                  frame1(c,d,:) = [153,153,153];
                      end
                  end
              end
          end            
      end    

      if i == 760

          for a = 300 :2: 303;
              for b = 356 :2: 385;
                  for c = 301 :2: 303;
                      for d = 357 :2: 385;

                      frame1(a,b,:) = [153,153,153];
                      frame1(c,d,:) = [153,153,153];

                      end
                  end
              end
          end 

          for a = 300 :2: 303;
              for b = 357 :2: 385;
                  for c = 301 :2: 303;
                      for d = 356 :2: 385;

                  frame1(a,b,:) = [0,0,0];
                  frame1(c,d,:) = [0,0,0];
                      end
                  end
              end
          end  
      end

          for x = 1 : 478;            
              for y = 1 : 640;

                  if frame1(x,y,1) == frame1(x,y,2) && frame1(x,y,2) == frame1(x,y,3) && frame1(x+1,y,1) == frame1(x+1,y,2) && frame1(x+1,y,2) == frame1(x+1,y,3) && frame1(x+2,y,1) == frame1(x+2,y,2) && frame1(x+2,y,2) == frame1(x+2,y,3)

                      figure; imagesc(frame1);
                      title(['Frame ', num2str(i)])

                      xlabel('x-axis');
                      ylabel('y-axis');

                      coordinate = [x y]

                      frame1 = read(mov, i+1);

                  end

              end
          end

end

toc

Thanks

Answer 1

[Richard Brown]

Un-nest your loops - your a,b and c,d loops are independent of each other. What you're doing is running your inner two loops gazillions of times more than you need to. I.e. replace your four-level loops with these:

for a = ...
  for b = ...
    frame1(a, b, :) =...
  end
end

for c = ...
  for d = ...
    frame1(c, d, :) =...
  end
end

[Walter Roberson]

And your code

for c = 301 :2: 303;

for d = 354 :2: 381;

frame1(c,d,:) = [0,0,0];

end

end

can be replaced by

frame1(301 :2: 303,354 :2: 381,:) = 0;

with no loop at all.

[Peony Lai]

Thankyou.

I had try this but the time is also the same. Didn't decrease, any other method? Thanks

[Peony Lai]

Dear Walter Roberson,

Thankyou, I try this but have a error,

"??? Subscripted assignment dimension mismatch."

so that the program cannot run