How does MATLAB pick colors from Colormap?

Hi everyone,

when you plot

c = load('count.dat'); c=c'; Y = c(1:3,1:6); figure; bar(Y);

you get 6 different colors in the bar graph

when you plot c = load('count.dat'); c=c'; Y = c(1:3,1:6); figure; bar(Y);

you get 3 different colors.

How does MATLAB pick which colors to plot? And how can I extract the RGB colors (ie [0 0 1],etc) that were used?

Thanks

Answer 1

[Image Analyst]

It's determined by the default "ColorOrder" of the axes. My demo shows how to retrieve the initial colors and change them to something you want.

% Unless you specify the 'Color' property when you plot,
% plots are plotted according to the 'ColorOrder' property of the axes.
% This demo shows how you can change the default color order of plots.

clc;    % Clear the command window.
close all;  % Close all figures (except those of imtool.)
clear;  % Erase all existing variables.
workspace;  % Make sure the workspace panel is showing.
fontSize = 18;

% Make 20 plots, with 25 data points in each plot.
numberOfDataSets = 20;
x = 1:25;
y = rand(numberOfDataSets, length(x));
% These y would all be on top of each other.
% Separate the plots vertically.
offsets = repmat((1:numberOfDataSets)', [1, length(x)]);
y = y + offsets; 

% Get the initial set of default plot colors.
initialColorOrder = get(gca,'ColorOrder') % Initial

% See what the colors look like when plotted:
subplot(2, 1, 1);
plot(x,y, 'LineWidth', 3);
grid on;
caption = sprintf('%d plots with the Initial Default Color Order (Note the repeating colors)', numberOfDataSets);
title(caption, 'FontSize', fontSize);
xlabel('X', 'FontSize', fontSize);
ylabel('Y', 'FontSize', fontSize);

% Enlarge figure to full screen.
set(gcf, 'units','normalized','outerposition',[0 0 1 1]); % Maximize figure.
% Give a name to the title bar.
set(gcf,'name','Image Analysis Demo','numbertitle','off')

choice = menu('Which ColorOrder do you want?', 'jet', 'random', 'hsv', 'hot', 'cool', 'spring', 'summer',...
  'autumn', 'winter', 'lines', 'gray', 'bone', 'copper', 'pink');

% Make a new axes:
subplot(2, 1, 2);

% Create a new colormap that will define the new default color order property.
switch choice
  case 1
    newDefaultColors = jet(numberOfDataSets);
  case 2
    newDefaultColors = rand(numberOfDataSets, 3);
  case 3
    newDefaultColors = hsv(numberOfDataSets);
  case 4
    newDefaultColors = hot(numberOfDataSets);
  case 5
    newDefaultColors = cool(numberOfDataSets);
  case 6
    newDefaultColors = spring(numberOfDataSets);
  case 7
    newDefaultColors = summer(numberOfDataSets);
  case 8
    newDefaultColors = autumn(numberOfDataSets);
  case 9
    newDefaultColors = winter(numberOfDataSets);
  case 10
    newDefaultColors = lines(numberOfDataSets);
  case 11
    newDefaultColors = gray(numberOfDataSets);
  case 12
    newDefaultColors = bone(numberOfDataSets);
  case 13
    newDefaultColors = copper(numberOfDataSets);
  otherwise
    newDefaultColors = pink(numberOfDataSets);
end
% Note: You can build your own custom order if you want, 
% just make up a array with numberOfDataSets rows and 3 columns
% where each element is in the range 0-1.

% Apply the new default colors to the current axes.
set(gca, 'ColorOrder', newDefaultColors, 'NextPlot', 'replacechildren');

% Now get the new set of default plot colors.
% Verify it changed by printing out the new default color set to the command window.
newColorOrder = get(gca,'ColorOrder')

% Now plot the datasets with the changed default colors.
plot(x,y, 'LineWidth', 3);
grid on;
caption = sprintf('%d plots with the New Default Color Order', numberOfDataSets);
title(caption, 'FontSize', fontSize);
xlabel('X', 'FontSize', fontSize);
ylabel('Y', 'FontSize', fontSize);

msgbox('Done with ColorOrder demo!');

[Rainer]

Thanks! This is helpful.

Answer 2

[Honglei Chen]

You can see the order of color by doing

get(gca,'ColorOrder'）