How do you display a dynamically changing colormap in the app designer?

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Dimitar Dyankov 2022-5-3

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评论： Dimitar Dyankov 2022-5-7

Hello, I'm making an app where one window shows a dynamically changing colormap. Specifically, I have a 3D array frame_recording with dimensions 5x10x5000, and I'm running a while loop so that in the n-th iteration, the matrix frame_recording(:,:,n) is displayed in the window in the form of a colormap. I'm using imagesc for this, so something like this:

while(app.numFrame <= app.recording_duration)

imagesc(app.UIAxes, app.frame_recording(:,:,app.numFrame));

colormap(app.UIAxes,'jet');

app.numFrame = app.numFrame + 1;

end

The problem is that there is a large delay when displaying the image, I expect the colormap to change every few milliseconds but instead it takes around 0.3-0.4 seconds. I saw an app made in GUIDE that uses the command set(app.UIAxes, 'CData', app.frame_recording(:,:,app.numFrame) to display it and it works much better, but I get an error that 'CData' is not a valid property name for the set function (I'm using the newer app developer so maybe that's the issue). Is there any other way to make sure the colormap is properly displayed for each iteration in the loop?

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Answer 1

Monica Roberts 2022-5-3

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The 'CData' is on the imagesc object, which is the child of the axes. You could do a few things:

%% Grab the CData from the axes
set(app.UIAxes.Children,'CData',app.frame_recording(:,:,app.numFrame))

Or

%% Give the imagesc a handle to change
im = imagesc(app.UIAxes, app.frame_recording(:,:,app.numFrame));
colormap(app.UIAxes,'jet'); 
while(app.numFrame <= app.recording_duration)             
    set(im,'CData', app.frame_recording(:,:,app.numFrame))
    drawnow % You might need a drawnow to update the chart
    app.numFrame = app.numFrame + 1;
end