Apparent imshow memory leak?

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Sean
Sean on 17 Nov 2011
Commented: BC on 18 Mar 2021
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
  1 Comment
Jan
Jan on 17 Nov 2011
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.

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Accepted Answer

Jan
Jan on 17 Nov 2011
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
  1 Comment
Sean
Sean on 17 Nov 2011
Thanks!
I didn't realize you could do that. It not only eliminated the memory leak, but it updates a whole lot faster too.

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More Answers (2)

Image Analyst
Image Analyst on 17 Nov 2011
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;
  2 Comments
BC
BC on 18 Mar 2021
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!

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Yunjin Chen
Yunjin Chen on 21 Jun 2017
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.

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