drawnow() causing very slow display of images

조회 수: 38 (최근 30일)
Karl
Karl 2014년 2월 18일
댓글: Yu Liu 2020년 5월 13일
Hi all,
I've read several other questions on this but didn't find a satisfactory answer. My apologies however, if this is already up.
I am building a GUI to display processed video. I do this using
imshow(image,'Parent',axes)
then
drawnow
for each frame in a loop. It is VERY slow. Approx 0.5 seconds per frame (~12 seconds to display 1 second of video in real time). It also accounts for half my total processing time per frame.
Can I make it faster?
Any help is greatly appreciated!!
Cheers, KB

채택된 답변

Image Analyst
Image Analyst 2014년 2월 18일
I solved that problem with older versions of MATLAB by putting in a "cla" or "cla('reset')" into the code just before the imshow. Evidently with older versions sometimes the images "stack up" and are all in there and you're just piling one on top of another and it gets slower and slower as it runs out of memory. Try that and let me know if it speeds it up.
  댓글 수: 7
Karl
Karl 2014년 2월 20일
Updating CData was the answer I needed (I just had to implement it poperly). MY GUI is now running much faster. Example code pasted below, maybe it will help someone else.
Thanks very much Image Analyst :)
Updating CData vs imshow() example code:
%%Setup video
filename = 'your_video_here.mp4';
vidObj = VideoReader(filename);
%%Display first frame and setup handle to image
frame = read(vidObj, 1);
figure;
h = imshow(frame);
%%Loop through subsequent frames and refresh 'CData'
for k = 1:1000
tic
frame = read(vidObj, k);
set(h,'Cdata',frame);
drawnow
toc
end
for k = 1:1000
tic
frame = read(vidObj, k);
imshow(frame)
drawnow
toc
end
Yu Liu
Yu Liu 2020년 5월 13일
It works ! Thanks !

댓글을 달려면 로그인하십시오.

추가 답변 (1개)

David Sanchez
David Sanchez 2014년 2월 18일
I solved a similar issue by adding a very short pause, this will clean up the buffer and speed up the pseudo-video. Add:
pause(0.001)
right after drawnow
  댓글 수: 1
Karl
Karl 2014년 2월 18일
Hi David,
Thanks for the suggestion. Unfortunately it has not helped me :( in fact it made execution a little slower.

댓글을 달려면 로그인하십시오.

제품

Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!

Translated by