MATLAB App Designer: drawnow() is extremely slow

I'm trying to update an image window every few milliseconds in MATLAB's app designer, but the drawnow() function is working very slowly. The same code is working much more quickly outside of the app designer environment. I read this in a separate thread:

Appdesigner (or specifically UIFigure) employs a HTML/Javascript layer which is less efficient than the standard matlab figure.

And I think this may be the root of my problem. Is there a workaround? Any other way to quickly update an image window?

Thanks

Answer 1

[Adam Danz]

drawnow() updates all existing graphics. The more graphics that exist, the more updating.

You could try setting the limit rate so that graphics are refreshed less frequently: drawnow limitrate

It's not clear why graphics need to be repeatedly updated but in some contexts, animating your data is a lot faster and cleaner with one of the animation methods such as animatedline.

[Sam Nadjari]

Hi Adam, thanks for your quick reply. Those solutions are useful in many similar situations, but they don't really apply to my case, so I'll add some information here:

I'm only using one plot and I'm trying to capture images taken by a scientific camera at a quick rate and update the plot to show each new image as it's captured.

[Adam Danz]

That's helpful info - let's get a little more. This is the process I'm imagining, you can correct my imagination where it goes wrong.

So, you press a button that tells a camera to start rapidly taking photos. The camera sends each photo back to the app and you update the axes to show the new image while destroying the previous image.

What rate is the camera taking the photos? How fast are the photos arriving to your app? Is it a set number of photos (how many?) or does the process continue until you tell the camera to stop (how long?)? What's the size of these photos? What function are you using to plot them? Is your code doing anything repeatedly that is redundant? How are you updating the images? Would it be possible to collect all of the photos and then show the sequence or does it have to be in realtime? How are the incoming photos stored while witing for the dispaly to refresh?

[Sam Nadjari]

Yes, that just about describes the process. The camera will be capturing photos with frame rates ranging from 15fps to 1000fps. I'm not imagining that I'll be able to update the plot 1000x per second, and I know I might not even be able to update 15x per second. So, I'm planning on plotting only plotting a small fraction of the images, maybe every 1000 or every 100, depending on the frequency. The image acquisition process continues until the user presses a 'stop' button on the GUI, the photos are 640x480 grayscale images, and the plot update needs to occur in realtime. The photos are simply stored as 2D arrays.

The issue is that drawnow() just takes way too long to update the plot, far longer than it would in regular MATLAB (not app designer). For this reason, I can't update the plot with the frequency that I'd like to, and I miss a great deal of frames during the plot updating process.

[Adam Danz]

I see. Have you tried the limit rate and no-callback options in drawnow()?

drawnow limitrate nocallbacks

Also, try refreshdata()

[Sam Nadjari]

drawnow limitrate works great for my purposes. It plots every few frames acquired without significantly slowing down the program. I will also give refreshdata() a try next time I get in the lab. Thanks so much for your help.

[Adam Danz]

Good! If setting the limitrate in drawnow works I wouldn't bother trying the refreshdata method because you'll have to do some restructuring of your code and with frame rates of up to 1000fps, I doubt it would be sufficient.