Try this:
% Demo by Image Analyst
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;
markerSize = 40;
% Read in original RGB image and display it.
originalImage = imread('peppers.png');
subplot(2, 1, 1);
imshow(originalImage);
impixelinfo;
title('Original Image', 'FontSize', fontSize)
% Create indexed image with 6 colors.
numColors = 6;
[indexedImage, cmap] = rgb2ind(originalImage, numColors);
% Save it to disk.
imwrite(indexedImage, cmap, 'indexedImage.png');
% Read indexed image back in from disk.
[recalledImage, storedColorMap] = imread('indexedImage.png');
% Display it.
subplot(2, 1, 2);
imshow(recalledImage, 'Colormap', storedColorMap);
caption = sprintf('Indexed Image with %d Colors', numColors);
title(caption, 'FontSize', fontSize)
% Display color bar and adjust range from 0-255 to 0-numColors.
colorbar;
caxis([0, numColors])
impixelinfo;
% Maximize figure window.
g = gcf;
g.WindowState = 'maximized';
