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

I expect you could persuade Matlab to draw that, if you look at the File Exchange you may find someone has already written the code. But it would be a lot easier, if you don't have the code, to use MS Excel.

EDIT: So I gave this some more thought and here's what I came up with. I've not mastered posting graphics to SO, so trust me, this will lead you towards a solution. But it would honestly be easier with Excel.

First define a matrix with your data values; I call the matrix G in the following. Then execute the commands:

image(G); 
colormap(gray)

Now, I had to do some fiddling around, rescaling the data, to get a good graphic, but this should produce a gray-scale plot with numeric axes. Now, go to your figure window and open the plot tools.

Select the X axis and hit the Ticks button. All you have to do now is edit the labels to the texts that you want. Do the same for the Y axis. Write the numbers in the squares on the plot -- use the Text Box from the Annotations menu.

After a lot of fiddling about you'll have the graphic you want. At this point, I suggest that you choose the menu command File | Generate M-File and do just that. If you want to create such graphics programmatically in future just turn the generated M file into a proper function that does what you want.

But it's still a lot easier in Excel.

Answer 2

If you only care about looking at zero/non-zero entries in your matrix (e.g. if it's sparse), use spy.

Else, use imagesc.

PS: I can't access your image

Answer 3

h = imagesc(magic(8))
impixelregion(h)

http://www.mathworks.com/access/helpdesk/help/toolbox/images/ref/impixelregion.html

Requires Image Processing Toolbox

Answer 4

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, you can find some submissions on the MathWorks File Exchange that can rotate the tick label text, like XTICKLABEL_ROTATE from Brian Katz.