Problem of generating 4 sub-images

I want to divide a color image into 4 sub-images which are also needed to be color images. However, I got the wrong images for my implementation. Please help me. Thanks!

    % I= double(imread('2.jpg'));
% [m,n] = size(I);
% 
% r = I(:,:,1); % Get the RED matrix
% g = I(:,:,2); % Get the GREEN matrix
% b = I(:,:,3); % Get the BLUE matrix
% 
% [m,n] = size(r);
% 
% imgr{1} = r(1:m/2, 1:n/2);
% imgr{2} = r(m/2+1:m, 1:n/2);
% imgr{3} = r(1:m/2, n/2+1:n);
% imgr{4}= r(m/2+1:m, n/2+1:n);
% 
% imgg{1} = g(1:m/2, 1:n/2);
% imgg{2} = g(m/2+1:m, 1:n/2);
% imgg{3} = g(1:m/2, n/2+1:n);
% imgg{4}= g(m/2+1:m, n/2+1:n);
% 
% imgb{1} = b(1:m/2, 1:n/2);
% imgb{2} = b(m/2+1:m, 1:n/2);
% imgb{3} = b(1:m/2, n/2+1:n);
% imgb{4}= b(m/2+1:m, n/2+1:n);
% 
% final_image1(:,:,1)= imgr{1};
% final_image1(:,:,2)= imgg{1};
% final_image1(:,:,3)= imgb{1};
% 
% final_image2(:,:,1)= imgr{2};
% final_image2(:,:,2)= imgg{2};
% final_image2(:,:,3)= imgb{2};
% 
% final_image3(:,:,1)= imgr{3};
% final_image3(:,:,2)= imgg{3};
% final_image3(:,:,3)= imgb{3};
% 
% final_image4(:,:,1)= imgr{4};
% final_image4(:,:,2)= imgg{4};
% final_image4(:,:,3)= imgb{4};
% 
% filename = {final_image1,final_image2,final_image3,final_image4};
% q={'a1.bmp','a2.bmp','a3.bmp','a4.bmp'};
% 
% for i=1:4   
%     imwrite(filename{i},q{i},'bmp');
% end

Answer 1

[Simon]

Hi!

What exactly is going wrong?

[gg]

The program cannot generate four sub-images properly. See as the attachments.

[Simon]

Hi!

The RGB values are unsigned integers between 0 and 255 (aka uint8). Change your code to use this. Read without conversion to double:

I= imread('2.jpg');

Then all following arrays are uint8 as well (final_image1, ...). Be sure to clear your workspace. Otherwise you will have an implicit conversion if final_image1 is of class double and you assign an uint8 variable to it!

[gg]

Great, I did this.It works. Thank you, Simon!

      % code
% I= imread('2.jpg');
% [m,n] = size(I);
% 
% r = uint8 (I(:,:,1)); % Get the RED matrix
% g = uint8 (I(:,:,2)); % Get the GREEN matrix
% b = uint8 (I(:,:,3)); % Get the BLUE matrix
% 
% [m,n] = size(r);
% 
% imgr{1} = r(1:m/2, 1:n/2);
% imgr{2} = r(m/2+1:m, 1:n/2);
% imgr{3} = r(1:m/2, n/2+1:n);
% imgr{4}= r(m/2+1:m, n/2+1:n);
% 
% imgg{1} = g(1:m/2, 1:n/2);
% imgg{2} = g(m/2+1:m, 1:n/2);
% imgg{3} = g(1:m/2, n/2+1:n);
% imgg{4}= g(m/2+1:m, n/2+1:n);
% 
% imgb{1} = b(1:m/2, 1:n/2);
% imgb{2} = b(m/2+1:m, 1:n/2);
% imgb{3} = b(1:m/2, n/2+1:n);
% imgb{4}= b(m/2+1:m, n/2+1:n);
% 
% final_image1(:,:,1)= imgr{1};
% final_image1(:,:,2)= imgg{1};
% final_image1(:,:,3)= imgb{1};
% 
% final_image2(:,:,1)= imgr{2};
% final_image2(:,:,2)= imgg{2};
% final_image2(:,:,3)= imgb{2};
% 
% final_image3(:,:,1)= imgr{3};
% final_image3(:,:,2)= imgg{3};
% final_image3(:,:,3)= imgb{3};
% 
% final_image4(:,:,1)= imgr{4};
% final_image4(:,:,2)= imgg{4};
% final_image4(:,:,3)= imgb{4};
% 
% filename = {final_image1,final_image2,final_image3,final_image4};
% q={'a1.bmp','a2.bmp','a3.bmp','a4.bmp'};
% 
% for i=1:4   
%     imwrite(uint8(filename{i}),q{i},'bmp');
% end

    end

[Simon]

You do not neccesarily need the "uint8" conversion of "I" upon splitting the image. If "I" was not defined as double before it will automatically be of class uint8 after "imread".

[Image Analyst]

Wow, you really like to have a lot of code don't you? You could have done it in far less space simply by using imcrop() as I and David recommended. See demo code that I added in my answer to show you how simple it can be.

Answer 2

[Image Analyst]

Why not simply use imcrop() ? It would take far far fewer lines of code.

And when you do n/2, if n is an odd number, you'll get a .5 fraction off the end of the number and that will not let you do 1:n/2, so you need to do

n1 = floor(n/2);
n2 = n1+1;

Then go from 1 to n1 and from n2 to end.

[rows, columns, numberOfColorChannels] = size(rgbImage);
c1 = floor(columns/2); % Middle column
c2 = c1+1;
r1 = floor(rows/2); % Middle row
r2 = r1+1;
upperLeft = imcrop(rgbImage, [1, 1, c1, r1]);
upperRight = imcrop(rgbImage, [c2, 1, c1, r1]);
lowerLeft = imcrop(rgbImage, [1, r2, c1, r1]);
lowerRight = imcrop(rgbImage, [c2, r2, c1, r1]);

See attached for a full blown demo using MATLAB standard demo image.

Answer 3

[David Sanchez]

I = your_image;
[r c l] = size(I); % image dimensions
r2 = floor(r/2); 
c2 = floor(c/2);
I1 = imcrop(I,[1 r2 1 c2];
I2 = imcrop(I,[r2+1 r 1 c2]);
I3 = imcrop(I,[1 r2 1 c2+1 c]);
I4 = imcrop(I,[r2+1 r c2+1 c]);

[gg]

 I have tried it. But there are some mistakes to implement it.

 if true
    % code
% I= imread('2.jpg');
% [m,n] = size(I);
% 
% % I = your_image;
% [r c l] = size(I); % image dimensions
% r2 = floor(r/2); 
% c2 = floor(c/2);
% tempI{1} = imcrop(I,[1 r2 1 c2]);
% tempI{2} = imcrop(I,[r2+1 r 1 c2]);
% tempI{3} = imcrop(I,[1 r2 1 c2+1 c]);
% tempI{4}= imcrop(I,[r2+1 r c2+1 c]);
% q={'a1.bmp','a2.bmp','a3.bmp','a4.bmp'};
% 
% for i=1:4   
%     imwrite(uint8(tempI{i}),q{i},'bmp');
% end

end