how to convert grey image to RGB

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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);
P(:,:,K) = dicomread(petname);
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?

Accepted Answer

Jan
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 Comments
mohd akmal masud
mohd akmal masud on 10 Jan 2021
Hi Jan,
i have change my coding accordingly your suggestion. But my image still grey as picture attached.
clc
clear all
P = zeros(103, 103, 60);
for K = 1 : 60
K_file=30+10*K;
petname = sprintf('I%d.dcm', K_file);
P(:,:,K) = dicomread(petname);
scale = 130/103 ;
Pi(:,:,K) = imresize(P(:,:,K),scale) ; % where P is your 103*103 3D matrix
end
rgbImage = gray2rgb(Pi);
imshow3D(rgbImage);
below is my function i changed.
function [Pi]=gray2rgb(Pi)
%Gives a grayscale image an extra dimension
%in order to use color within it
[r,c,m] = size(Pi);
rgbImage = repmat(reshape(Pi / 255, [r, c, 1, m]), [1, 1, 3, 1]);
end
CAN HELP ME?
Jan
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?

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More Answers (2)

Image Analyst
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.
  8 Comments
john
john on 10 Jan 2022
Edited: john on 10 Jan 2022
how do i convert grayscale image to same color image but it should be an rbg image?
I tried the above function which u gave. My input was a grayimage with just 0 and 255 values when i used above function and runned the program it got converted to blue and brown. But i want the same original image but it should be an rgb so how do i get it?
Image Analyst
Image Analyst on 10 Jan 2022
@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.

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Jamal Nasir
Jamal Nasir on 28 Feb 2023
Moved: Image Analyst on 28 Feb 2023
there is no traditional method to convert gray image to color image
this need using machine learning for prediction the pixel value depend on the region in
similar sense
  1 Comment
Image Analyst
Image Analyst on 28 Feb 2023
He has a 60 channel hyperspectral image, as you can see from his code. One can use one of the strategies in the attached paper to convert multiple spectral channels into an RGB image.

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