Try : rgbImage(i,j,:)=im(i,j,:)

for the same location and all 3 pixel values (R,G,B) in a for/while loop

'im' is a gray image or color image?

If 'im' is a gray image, it just has one channel. That means im(i,j,:) is a number not a (R,G,B) array.

Therefore, the result of the code: rgbImage(i,j,:) = im(1,1,:) is R=G=B=im(i,j,:). Because R,G,B are same, the pixel is shown as a gray pixel.

After code: rgbImage(i,j,:) = im(1,1,:);

Try: rgbImage(i,j,:), and check R,G,B whether are same.

In matlab, if you let an array be equal to a number, each element of the array will be the number.

Why you don't save a copy of your original image. And you can do changes on one of them by keeping one originally. So you can get both changed and original pixels.

the code is:

for i=1:40;

for j=1:40;

rgbImage(i,j,:)

rgbImage(i,j,:) = im(160+i,110+j,:);

rgbImage(i,j,:)

end

end

the output before is: ans rgbimage (:,:,:) =154, 198, 233

and after is: ans rgbimage (:,:,:) =0, 0, 0

the images: rgbImage and im are colored images

check the foemat of rgbImage and im, maybe different format coursed.

And alse try: im(160+i, 110+j, :) , check the pixel values of im. Maybe this in this area, the im is a black.

for i=1:40;

for j=1:40;

rgbImage(i,j,:)

rgbImage(i,j,:) = im(160+i,110+j,:);

rgbImage(i,j,:)

end

end

the output before is: ans rgbimage (:,:,:) =154, 198, 233

and after is: ans rgbimage (:,:,:) =0, 0, 0

the images: rgbImage and im are colored images