How to capture frame (image) using webcam at specific time interval (e.g. at 100ms or 10 frames per second) in matlab app designer?

One state button is starting the webcam camera and I am previewing the video camera output in the UIAxes.

function StartCameraButtonValueChanged(app, event)
            value = app.StartCameraButton.Value;
            app.Camera = webcam(value);
            if value == true
                app.frame = snapshot(app.Camera);
                app.captureCurrentVideo = image(app.UIAxes, zeros(size(app.frame), 'uint8'));
                preview(app.Camera, app.captureCurrentVideo);
            end
end

Now, i want to capture and store (in variables) only 10 frames per second (in the loop) from the webcam at every seconds, to get histogram of it and update the UIAxes2 to see the liv ehistogram of 10 images per seconds, how can i modify or add some code to perform this task ?

Answer 1

[Eric Delgado]

Wow... it is simple, but you have a lot of code to write. :)

You need to create some properties in your app to store the images and others to control the index, snapshot flag...

For example:

% Properties
app.imgFlag  = false;
app.imgIdx   = 1;
app.imgArray = repmat({[]}, 1, 5);  % Five images
app.imgTime  = 1;                   % 1 second

% StateButtonCallback
if app.StateButton.Value
    app.imgFlag = true;
else
    app.imgFlag = false;
end

% Update imgArray
function Fcn_imgSnapshot(app)
    app.Camera = webcam;
    
    while app.imgFlag
        tic
        app.imgArray(app.imgIdx) = snapshot(app.Camera);
        
        if app.imgIdx < numel(app.imgArray)
            app.imgIdx = app.imdIdx+1;
        else
            app.imgIdx = 1;        
        end
        
        t1 = toc;
        if t1 < app.imgTime
            pause(app.imgTime-t1)
        end
    end
end

Or maybe create a timer, so you can avoid the loop.

% Properties
app.imgIdx   = 1;
app.imgArray = repmat({[]}, 1, 5);

% Startup of your app
app.tmr = timer('Period', 4, 'ExecutionMode', 'fixedRate', 'TimerFcn', @app.Fcn_imgSnapshot)

% TimerButtonCallback (StateButton)
if app.TimeButton.Value
    start(app.tmr)
else
    stop(app.tmr);
end

% Update imgArray
function Fcn_imgSnapshot(app)
    app.imgArray(app.imgIdx) = snapshot(app.Camera);
    
    if app.imgIdx < numel(app.imgArray)
        app.imgIdx = app.imdIdx+1;
    else
        app.imgIdx = 1;        
    end
end

[Venis Prajapati]

Yes, its working, but overall i am getting slow outputs in this program.