When I use the command 'pcolor' on a large matrix I get a blank plot - does anyone know why?

When I use the command 'pcolor' on a large matrix I get a blank plot - does anyone know why?

I want to use 'pcolor' to plot a matrix of 6144 by 150 - if I just generate a matrix of this size using a random generator e.g.: X=rand(6144,150)

and then plot: pcolor(X)

I get a blank screen but pcolor works fine for e.g.: X=rand(25,10)

Please help. Thanks

Answer 1

[Walter Roberson]

Is it blank, or is it black?

h = pcolor(X);
set(h, 'EdgeColor', 'none')

[Walter Roberson]

pcolor() is really just

surf()
view(2)

But by default surf() used black edges between faces. The black edges stay a constant width as you shrink the size of the faces to fit more faces onto the display; after a point, the black edges take over everything. So you want to turn off the edges by setting the surface EdgeColor property to 'none'

[Jonathan Silas]

Makes sense - thank you for your help!

[Minh Tran]

Hi Walter. What do you mean by "face"? Just the "filled square" right?

[Walter Roberson]

Yes, faces refer to the filled squares.

Answer 2

[Jonathan Silas]

Thank you! Yes - it was black not blank. That solved it... what did you do?

[Margaret Zhang]

This was asked 5 years ago.... but just incase for anyone in the future lol. The set edgecolor essentially took out all of the borders of the graph so that you can see the colors. It looked black because the boxes of the matrix were so small that with a border on each block, it looked black.

[Walter Roberson]

Or see my explanation from back then at https://www.mathworks.com/matlabcentral/answers/371168-when-i-use-the-command-pcolor-on-a-large-matrix-i-get-a-blank-plot-does-anyone-know-why#comment_512783