Apparent imshow memory leak?

Hello,

I have some code that captures and displays images repeatedly for some time, and I noticed that it continually eats up more and more memory (until it crashes).

I did some investigating and provided I don't bother to display the images, there do not appear to be any problems.

I determined that imshow() appears to be the cause of my woes, and I am hoping that there is a technique to resolve the problem.

The following code should demonstrate the issue:

x=rand(500,700,3);
for n=1:10000
    imshow(x);
    %drawnow;
    if mod(n,500) == 0
        memory
    end
    %cla
end

Does anyone know how to stop imshow() from eating up my memory? (or) Does anyone know how to display an image another cleaner way?

Thanks in advance, Sean

[Jan]

I've started your example in the command line of Matlab 2009a/64 in Windows 7. Now I cannot stop the program using Ctrl-C. I cannot kill the process due to unsaved changes in some open M-files, but the editor is unresponsive also.

But I do not see an increase in the occupied memory.

Answer 1

[Jan]

You can create the image once and update the CData only afterwards:

x = rand(500,700,3);
imgH = imshow(x);
for n=1:10000
  set(imgH, 'CData', x);
  drawnow;
  if mod(n,500) == 0
      memory
  end
end

[Sean]

Thanks!

I didn't realize you could do that. It not only eliminated the memory leak, but it updates a whole lot faster too.

Answer 2

[Image Analyst]

You're basically storing all of those images in the same axes, one on top of another. Put this before imshow and it will be fine:

cla reset;

[Sean]

I tried what you suggested, and it improved the rate of memory loss from about 10MB per 1000 iterations to about 2MB per 1000 iterations.

Thanks. I'm still going to keep looking for a way to remove the loss altogether though. :)

[BC]

Just came here to say I was having issues with a loop giving me an "out of memory" error after a while - including this in my loop seems to have solved this issue for now, thanks!

Answer 3

[Yunjin Chen]

from https://stackoverflow.com/questions/36150047/matlab-imshow-how-to-free-memory-but-show-the-image

I bet you are doing something like

hold on
for ii=1:frames
    imshow(frame)
    drawnow
end

as most memory problems are due to this structure. If you hold on and never clear the figure, you will draw on top of whatever is there, but it will never get deleted. I suggest you remove the hold on if you are just drawing a single thing inside the loop, and if you are drawing more than one thing inside and you need the hold on, then add cla (clear axes) or clf after the drawnow, or in the begging of the loop.