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I have a RGB image which I am trying to complement without using the built-in function imcomplement(A).

R=A(:,:,1);% A is the input image
G=A(:,:,2);
B=A(:,:,3);
[r,c]=size(B);
for i=1:1:r
    for j=1:1:c
        R(i,j)=255-R(i,j); 
        G(i,j)=255-G(i,j);
        B(i,j)=255-B(i,j);
    end
end
new=cat(3,R,G,B);

This solution gives the expected output.

How can I do the same thing without using the cat function? This is my current unsuccessful attempt:

[r,c]=size(B);
new=zeros(size(A,1),size(A,2),'uint8');
for i=1:1:r
    for j=1:1:c
        for k=1:1:1
            new(i,j,k)=(255-G(i,j));
        end
    end
end
Dev-iL
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Wahid Molla
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    Rather than decompose and recompose channels, how about compute it all at once as an array operation: `new = 255 - A`. – Pascal Getreuer Oct 31 '20 at 19:50
  • As the Title suggests that I want to learn if it is possible to conact the the RGB channels without using the built in function . – Wahid Molla Nov 02 '20 at 16:31

1 Answers1

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As mentioned by @Pascal, the most straightforward solution is

new = intmax('uint8') - A;

If you insist on using loops (which I highly advise against in this case), these should work:

[r,c,s] = size(A);
new = zeros(r,c,s,'uint8'); % alternatively: zeros(r,c,s,'like',A);
for iR = 1:r % the middle :1: is implied
  for iC = 1:c
    for iS = 1:s % s stands for "slice"
      new(iR, iC, iS) = intmax('uint8') - A(iR, iC, iS);
    end
  end
end

for iR = 1:r
  for iC = 1:c
    new(iR, iC, 1) = intmax('uint8') - R(iR, iC);
    new(iR, iC, 2) = intmax('uint8') - G(iR, iC);
    new(iR, iC, 3) = intmax('uint8') - B(iR, iC);
  end
end

As you can see, all of the above solutions do not use the cat function which you wanted to avoid.

Dev-iL
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  • Thank you for your wonderful illustration. This is my first Question on stackoverflow. that is why there were so much errors. – Wahid Molla Nov 03 '20 at 16:44