# how to convert grey image to RGB

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mohd akmal masud on 9 Jan 2021
Commented: Image Analyst on 10 Jan 2022 at 13:28
Hi all,
i have 60 slice grey image. how want to convert to RGB image?
as attached is my grey image (grey.jpg). rgb.jpg is from internet what i want like.
this is my coding, but got error.
P = zeros(103, 103, 60);
for K = 1 : 60
K_file=30+10*K;
petname = sprintf('I%d.dcm', K_file);
scale = 130/103 ;
Pi(:,:,K) = imresize(P(:,:,K),scale) ; % where P is your 103*103 3D matrix
end
rgbImage = gray2rgb(Pi);
imshow3D(rgbImage)
this is my function
function [Image]=gray2rgb(Image)
%Gives a grayscale image an extra dimension
%in order to use color within it
[m n]=size(Image);
rgb=zeros(m,n,3);
rgb(:,:,1)=Image;
rgb(:,:,2)=rgb(:,:,1);
rgb(:,:,3)=rgb(:,:,1);
Image=rgb/255;
end
BUT GOT ERROR.
Unable to perform assignment because the size of the left side is 130-by-7800 and the size of
the right side is 130-by-130-by-60.
Error in gray2rgb (line 6)
rgb(:,:,1)=Image;
Error in sliderspect1 (line 12)
rgbImage = gray2rgb(Pi);
I THINK MY function gray2rgb wrong.
can some one help me?

Jan on 9 Jan 2021
Your Pi is a [130 x 130 x 60] matrix, but your function gray2rgb() expects a 2D matrix as input. It is not clear how you want to convert the 60 layers of the image data to RGB channels.
Maybe you want:
[r,c,m] = size(Pi);
rgbImage = repmat(reshape(Pi / 255, [r, c, 1, m]), [1, 1, 3, 1]);
##### 2 CommentsShowHide 1 older comment
Jan on 10 Jan 2021
Yes, of course the image is grey, because the original images contain the grey level information only. If the value of each pixel of the input is used for all 3 RGB channels, the output looks grey also.
Which information do you want to use to define the colors?

Image Analyst on 10 Jan 2021
Try
function rgbImage = gray2rgb(grayImage)
cmap = jet(256); % Or whatever one you want.
rgbImage = ind2rgb(grayImage, cmap); % Convert gray scale image into an RGB image.
Image Analyst on 10 Jan 2022 at 13:28
@john if you have an image with just 0 and 255, and use ind2rgb() then you will end up with an RGB color image with only two colors - those colors being cmap(1,:) and cmap(255, :), which I guess are ble and brown for the colormap you used. There is no way to get back the original true color RGB image from only a gray scale version of it. as you can imagine, there are nearly an infinite number of color images that could be made from it. You'll just have to save your original RGB image if you want it later in your program.

R2020b

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