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how to change the color of an image?

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vittorio calbucci
vittorio calbucci on 26 Feb 2018
Answered: Image Analyst on 23 Mar 2018
I'm wondering how to change the color of a grayscale image to rgb. In particular given a grayscale image, obtained form mat2gray(matrix), i would like to assign a specific color (e.g. green) to those pixels with a gray value in a specific range and the color red to the other pixels. I'm using the map jet(255) with imshow but i'm not satisfied of the result. I would like to choose the threshold in order to select pixels to assign green color and pixels to assign red.

Answers (2)

Image Analyst
Image Analyst on 23 Mar 2018
You can either adjust your colormap and display the gray scale image with the proper colormap.
imshow(grayImage);
colormap(customColorMap);
OR you can create an RGB image using ind2rgb() with the proper colormap.
rgbImage = ind2rgb(grayImage, customColorMap);
Which way do you want to do it? If you can't figure it out, attach your gray scale image and tell us what intensity ranges you want to show up in which colors.

Klont
Klont on 23 Mar 2018
function M=rgbThreshold(M,greenRange)
% rgbThreshold
% jacob 2018-03-23
% check the inputs
narginchk(0,2);
if ~exist('M','var') || isempty(M)
M=rand(10);
end
if ~exist('greenRange','var') || isempty(greenRange)
greenRange=[.25 .75];
end
% Clamp M between zero and 1
mat2gray(M);
% make Red Green Blue matrices
[R,G,B]=deal(zeros(size(M)));
% decide which pixels are withing range
inrange=M>=min(greenRange) & M<=max(greenRange);
% paint pixels within range green
G(inrange) = M(inrange);
% paint pixels not in range red
R(~inrange) = M(~inrange);
% Merge the RGB channels for plotting
RGB=cat(3,R,G,B);
% Plot the image
image(RGB);
end

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