How to save image with custom colormap (imwrite problems)

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gapsna 2016-4-18

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https://ww2.mathworks.cn/matlabcentral/answers/279659-how-to-save-image-with-custom-colormap-imwrite-problems

评论： gapsna 2016-5-2

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

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采纳的回答

Image Analyst 2016-4-18

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https://ww2.mathworks.cn/matlabcentral/answers/279659-how-to-save-image-with-custom-colormap-imwrite-problems#answer_218438

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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Image Analyst 2016-5-1

在 MATLAB Online 中打开

You need to use a different colormap when you're creating the RGB image.

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;
s= load('cs_plot.mat')
cs_plot = s.cs_plot;
whos cs_plot
subplot(3, 2, 1);
imshow(cs_plot);
axis on;
title('Indexed Image with no colormap', 'FontSize', fontSize);
unique(cs_plot(:))
subplot(3, 2, 2);
histogram(cs_plot);
grid on;
title('Histogram', 'FontSize', fontSize);
cmap=[153 76 0; 0 128 255; 96 96 96; 224 224 224; 255 255 255; 0 0 0]/255;
h3 = subplot(3, 2, 3);
imshow(cs_plot);
title('Indexed Image', 'FontSize', fontSize);
colormap(h3, cmap);
colorbar
drawnow;
% Get an RGB image
colorMapForSaving = imresize(cmap,[256, 3], 'nearest');
rgbImage = ind2rgb(cs_plot, colorMapForSaving);
h4 = subplot(3, 2, 4);
imshow(rgbImage);
title('RGB Image', 'FontSize', fontSize);
drawnow;
filename = 'delete_me.png'
imwrite(rgbImage, filename);
% Recall from disk and see if it's okay.
rgbImage = imread(filename);
h4 = subplot(3, 2, 5);
imshow(rgbImage);
title('Recalled Image', 'FontSize', fontSize);
% Delete temporary file
delete(filename)