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convert matrix to rgb

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Philipp on 6 Aug 2012
Commented: DGM on 15 Jan 2023
dear matlab developers,
i have a double matrix (MxN). is there a way to convert it to RGB?
when i use imagesc(matrix), all the values are color coded and displayed, but is there a way to write the RGB values into a new array (MxNx3)?
br philipp

Accepted Answer

Matt Fig
Matt Fig on 6 Aug 2012
I wonder if this is what you mean, Philipp?
% Say this is the given matrix:
G = rand(10,10)*300 - 100;
% Use IMAGESC to plot G.
figure('pos',[100 100 1000 800]);
% colormap(copper) % You realize this affects final image (H)?
title('IMAGESC (MxN)')
% Now make an RGB image that matches display from IMAGESC:
C = colormap; % Get the figure's colormap.
L = size(C,1);
% Scale the matrix to the range of the map.
Gs = round(interp1(linspace(min(G(:)),max(G(:)),L),1:L,G));
H = reshape(C(Gs,:),[size(Gs) 3]); % Make RGB image from scaled.
image(H) % Does this image match the other one?
title('IMAGE (MxNx3)')
Mathieu on 12 Aug 2015
Thank you so Much Matt, very helpful!!
DGM on 15 Jan 2023
You could also use ind2rgb() with the desired colortable.
% create a 2D array that's not in standard image data scale
myarray = repmat(linspace(-1,1,200),[100,1]);
% create whatever color table
CT = jet(256);
% rescale to index range (multiple ways to do this)
%scaledpict = round(rescale(double(myarray),1,size(CT,1))); % R2017b+
%scaledpict = gray2ind(mat2gray(myarray),size(CT,1)); % IPT
scaledpict = round(1 + mat2gray(myarray)*(size(CT,1)-1));
% convert to RGB
outpict = ind2rgb(scaledpict,CT);
% display it
% or save it

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More Answers (3)

Jurgen on 1 May 2013
The FEX has mat2im and real2rgb. Can recommend both!
  1 Comment
Jurgen on 1 May 2013
Just noticed this thread was old...

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Image Analyst
Image Analyst on 6 Aug 2012
rgbImage = cat(3, redChannel, greenChannel, blueChannel);
Cast to uint8 if you want to display or save to a file. Scale to 0-255 if it's not already in that range. mat2gray() might help.

Walter Roberson
Walter Roberson on 6 Aug 2012


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