FIND and rgb image

I have rgb image (NxMx3) on which I want to mark some pixels in red. for that I have created a mask M (NxMx1), which values are all zeroes, except in the pixels I want to mark in red. I tried doing it using find, but it does not work like I wanted to and don't understand why.

for example, let say that

a=[1 2 3 4 5;6 7 8 9];
a=a./max(a(:));
img(:,:,1)=a;
img(:,:,2)=a;
img(:,:,3)=a;
M=[1 0 0 0;1 1 0 0 ];
[c,r]=find(M)
img(c,r,1)=1;
img(c,r,2)=0;
img(c,r,3)=0;

this give

img(:,:,1) =

      1.0000    1.0000    0.3000    0.4000    0.5000
      1.0000    1.0000    0.8000    0.9000    1.0000

img(:,:,2) =

           0         0    0.3000    0.4000    0.5000
           0         0    0.8000    0.9000    1.0000

img(:,:,3) =

           0         0    0.3000    0.4000    0.5000
           0         0    0.8000    0.9000    1.0000

instead of the wanted output, which is :

img(:,:,1) =

      1    0.2000    0.3000    0.4000    0.5000
      1        1     0.8000    0.9000    1.0000

img(:,:,2) =

      0   0.2000    0.3000    0.4000    0.5000
      0     0       0.8000    0.9000    1.0000

img(:,:,3) =

      0    0.2000    0.3000    0.4000    0.5000
      0       0      0.8000    0.9000    1.0000

Answer 1

[Image Analyst]

Try this:

a=[1 2 3 4 5; 6 7 8 9 10];
a=a./max(a(:));
rgbImage(:,:,1)=a;
rgbImage(:,:,2)=a;
rgbImage(:,:,3)=a;
subplot(1, 3, 1);
imshow(rgbImage);

% Create mask
mask = logical([1 0 0 0 0;1 1 0 0 0]);
subplot(1, 3, 2);
imshow(mask);

% Extract the individual red, green, and blue color channels.
redChannel = rgbImage(:, :, 1);
greenChannel = rgbImage(:, :, 2);
blueChannel = rgbImage(:, :, 3);
% Apply mask to make it 1 in the red channel and 0 in the green and blue channels.
redChannel(mask) = 1;
greenChannel(mask) = 0;
blueChannel(mask) = 0;

% Recombine separate color channels into a single, true color RGB image.
rgbImage = cat(3, redChannel, greenChannel, blueChannel);
subplot(1, 3, 3);
imshow(rgbImage);