MATLAB: How to save image with custom colormap (imwrite problems)

colorcolormapimageImage Processing Toolboximwritejpegpngtiff

Hello everyone, I am trying to save a large matrix who's cells contain one of 6 possible values (0, 50, 100, 150, 200, 255)(if needed those values can be changed). I also have a 6 by 3 matrix as color map: cmap=[153 76 0; 0 128 255; 96 96 96; 224 224 224; 255 255 255; 0 0 0]/255; (those colors need to stay as they are).

I try to save the image like this

imwrite(matrix, cmap, 'name.png');

but the image is saved with only two colors. I have tried different image types and different rang values for the matrix but no solution.

Can anyone help me with this?

Thank you very much.

Cheers,

Camilo

Best Answer

Try imwrite() and see if that works. Use imread() to see if the saved colormap comes back with only 2 colors, or all 6.

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How about this:

clc;    % Clear the command window.
close all;  % Close all figures (except those of imtool.)
clear;  % Erase all existing variables. Or clearvars if you want.
workspace;  % Make sure the workspace panel is showing.
format long g;
format compact;
fontSize = 20;
image1 = imread('image1.jpg');
% Get the dimensions of the image.  
% numberOfColorChannels should be = 1 for a gray scale image, and 3 for an RGB color image.
[rows, columns, numberOfColorChannels] = size(image1);
if numberOfColorChannels > 1
  % It's not really gray scale like we expected - it's color.
  % Use weighted sum of ALL channels to create a gray scale image.
  image1 = rgb2gray(image1); 
  % ALTERNATE METHOD: Convert it to gray scale by taking only the green channel,
  % which in a typical snapshot will be the least noisy channel.
  % grayImage = grayImage(:, :, 2); % Take green channel.
end
% This image is supposed to be binary.
image1 = image1 > 128;
imshow(image1);
hp = impixelinfo();
% Display the image.

subplot(2, 2, 1);
imshow(image1, []);
axis on;
hold on;
title('Image1', 'FontSize', fontSize, 'Interpreter', 'None');
drawnow;
hold on
image2 = imread('image2.jpg');
% Display the image.
subplot(2, 2, 2);
imshow(image2, []);
hp = impixelinfo();
axis on;
hold on;
title('Image2', 'FontSize', fontSize, 'Interpreter', 'None');
drawnow;
h3 = subplot(2, 2, 3:4);
% Mask the image using bsxfun() function
% maskedRgbImage = bsxfun(@times, image2, cast(image1, 'like', image2));
imshow(image1, []);
hp = impixelinfo();
hold on;
h=imshow(image2);
set(h,'Alphadata', 0.6);
axis on;
theColorMap = jet(256);
theColorMap(1,:) = 0; % First row is black.
theColorMap(end,:) = 1; % last row is white.
colormap(h3, theColorMap);
colorbar(h3);
caxis([0,0.6]);
title('Image1 with Image2 in overlay', 'FontSize', fontSize, 'Interpreter', 'None');
% Set up figure properties:
% Enlarge figure to full screen.
set(gcf, 'Units', 'Normalized', 'OuterPosition', [0, 0.05, 1, .95]);
% Get rid of tool bar and pulldown menus that are along top of figure.
% set(gcf, 'Toolbar', 'none', 'Menu', 'none');
% Give a name to the title bar.
set(gcf, 'Name', 'Demo by ImageAnalyst', 'NumberTitle', 'Off')

Best Answer

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