How can I implement block search in this program?

Hello all! I wanted to compare image al , with another image b, which is a block of image form the previous image al. I tried splitting image al block by block and storing them in 4 different matrices(and implement SSD), which I've programmed below. But when I run them, it looks like its into an infinite loop. Is there any other method to process blocks and match them? Please help.

clear all;
close all;

al = imread('testimage.jpg');
br = uint8(zeros(125, 125, 3));
br(1:126, 1:126,:) = al(80:205, 100:225 , :)

imtool(al); imtool(br);
al= rgb2gray(al);
al = im2double(al);

br= rgb2gray(br);
br = im2double(br);
for(i =1:1:126)
    for (j = 1:1:126)
        c(i,j) = al(i,j)
    end
end

for(i =99:1:225)
    for (j = 99:1:225)
        d(i,j) = al(i,j)
    end
end
for(i =99:1:225)
    for (j = 1:1:126)
        e(i,j) = al(i,j)
    end
end
for(i =1:1:126)
    for (j = 99:1:225)
        f(i,j) = al(i,j)
    end
end
        imtool(c); imtool(d); imtool(e); imtool(f)

[Stephen23]

You mention that you wish to "match" the blocks from the image. What exactly do you mean by this? Is pixel-wise RGB value equivalence a "match"?

Answer 1

[Stephen23]

MATLAB's feature called vectorization would be a great help, it allows you to perform operations on whole arrays, without requiring any loops. It is faster, neater, and less prone to bugs.

This means that

for(i =1:1:126)
    for (j = 1:1:126)
        c(i,j) = al(i,j)
    end
end

can simply be

c(1:126,1:126) = al(1:126,1:126);

or, if this is the first time that c is defined:

c = al(1:126,1:126);

This also applies to the two lines

br = uint8(zeros(125, 125, 3));
br(1:126, 1:126,:) = al(80:205, 100:225 , :)

where the first line really is not required:

br = al(80:205,100:225,:);

This introduction to indexing might be useful to read too:

http://www.mathworks.com/company/newsletters/articles/matrix-indexing-in-matlab.html

However you are working with image data, which often consists of 3D arrays. You will also need to consider what happens to that third array dimension.

Note that it is best to avoid i and j as a variable names, as these represent imaginary/complex values.

[Emmanuel]

Thanks!! Now my code snippet looks like this:

c(1:126 , 1:126, :) = al(1:126 , 1:126, :)
        d(1:126, 1:126,:) =  al(100:225, 100:225,:)
        e(1:126, 1:126,:) = al(100:225, 1:126,:)
        f(1:126, 1:126,:)  = al(1:126,100:225, :)

          imtool(c); imtool(d); imtool(e); imtool(f)

I got four image blocks :). Is there any other efficient algorithm that will help me in block matching. Also, from where can I learn about the algorithms? Any online tutorials or sources which you might help me. I'm a beginner in image processing and matlab and would like to learn more about them