MATLAB image processing

Question

How to convert an image to grayscale (Gray) to a color image (rgb)?

img=im2double(imread('37_M.jpg'));
figure(1),
imshow(img,[]),
title('original');
t=imgaussfilt3(img,0.2);
figure(2),
imshow(t,[]),
title('original filtro');
img2=rgb2gray(t);
figure(3),
imshow(img2,[]),
title('original gray');

I want a final image that is the junction of the img with the img2 after segmented and with contours, but as img is 3D and img2 2D do not know how to do.

Answer 1

You cannot convert grayscale images back to rgb because you do not have enough information. Many different combinations of RGB values convert to the same grayscale level, so if all you have is the grayscale level, then you cannot know which of the RGB values map exactly the same grayscale as the original RGB. In your case, you don’t need a color image, but only a 3-channel gray image (such as rgb format). Thus, you just need to turn the image into grayscale (1 channel) in 3-channel format.

For such you can use:

img2 = cat(3,img2,img2,img2);

or

img2 = repmat(img2,[1 1 3]);

Now both im and im2 images have the same format (check using size(img) and size(im2)).