How do I visualize a matrix with colors and values displayed?

Question

I want to create images like this from a double precision matrix using MATLAB.

Sample image:

http://twitpic.com/2xs943

Answer 1

You can create this sort of plot yourself pretty easily using the built-in functions imagesc and text and adjusting a number of parameters for the graphics objects. Here's an example:

mat = rand(5);           % A 5-by-5 matrix of random values from 0 to 1 imagesc(mat);            % Create a colored plot of the matrix values colormap(flipud(gray));  % Change the colormap to gray (so higher values are                          %   black and lower values are white)  textStrings = num2str(mat(:), '%0.2f');       % Create strings from the matrix values textStrings = strtrim(cellstr(textStrings));  % Remove any space padding [x, y] = meshgrid(1:5);  % Create x and y coordinates for the strings hStrings = text(x(:), y(:), textStrings(:), ...  % Plot the strings                 'HorizontalAlignment', 'center'); midValue = mean(get(gca, 'CLim'));  % Get the middle value of the color range textColors = repmat(mat(:) > midValue, 1, 3);  % Choose white or black for the                                                %   text color of the strings so                                                %   they can be easily seen over                                                %   the background color set(hStrings, {'Color'}, num2cell(textColors, 2));  % Change the text colors  set(gca, 'XTick', 1:5, ...                             % Change the axes tick marks          'XTickLabel', {'A', 'B', 'C', 'D', 'E'}, ...  %   and tick labels          'YTick', 1:5, ...          'YTickLabel', {'A', 'B', 'C', 'D', 'E'}, ...          'TickLength', [0 0]); 

And here's the figure this generates:

If you run into trouble with the x-axis tick labels you choose being too wide and overlapping one another, here's how you can handle it:

• Newer versions of MATLAB: Not sure which version this was added, but in newer versions axes objects now have the properties '{X|Y|Z}TickLabelRotation', which allow you to rotate the labels and fit them better.

• Older versions of MATLAB: For older versions you can find some submissions on the MathWorks File Exchange that can rotate the tick label text, like XTICKLABEL_ROTATE from Brian Katz.