how to change the color of an image?

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.

Answer 1

[Image Analyst]

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.

See my visual/interactive thresholding utility: https://www.mathworks.com/matlabcentral/fileexchange/29372-thresholding-an-image

Answer 2

[Klont]

 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