convert matrix to rgb

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

Answer 1

[Matt Fig]

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)?
subplot(1,2,1)
imagesc(G);
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.
subplot(1,2,2)
image(H)  % Does this image match the other one?
title('IMAGE (MxNx3)')

[Philipp]

Hi Matt, thanks for you helpful answer, it really addresses the problem I was struggling with. I found it also to be useful to create the lookup table directly from jet(1:1000) without the need of an interpolation.

br philipp

[Seth]

This is very helpful Matt - solved my problem as well - very efficiently I might add.

The only thing I would add is that if you don't want to display a figure during this process (just work with data), then you need to modify the following lines:

Change: C = colormap; % Get the figure's colormap.

To: C = jet(64); %State the name of the colormap and the number of levels

For whatever reason, the function "colormap" creates and displays an empty window where as directly defining the colormap by name and number of levels suppresses the creation of a new figure.

Thanks again for the great piece of code.

[Bruno]

Such beatiful peace of code. I'm very thankful!

[Mathieu]

Thank you so Much Matt, very helpful!!

[DGM]

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
imshow(outpict)

 % or save it
imwrite(outpict,'mypicture.png')

Answer 2

[Jurgen]

The FEX has mat2im and real2rgb. Can recommend both!

real2rgb

mat2im

double2rgb

[Jurgen]

Just noticed this thread was old...

Answer 3

[Image Analyst]

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.

Answer 4

[Walter Roberson]

http://www.mathworks.com/matlabcentral/fileexchange/7943-freezecolors-unfreezecolors