App Designer: How to use a camera in different Callbacks

Hello everybody,

I am using App Designer and try to implement a camera into my application.

I have one Callback in which I open a live stream from a camera, when a Button is pushed. To realise this, I use the following Code:

app.vid = videoinput('gentl', 1,'Mono8');
hImage = image(app.UIAxes,zeros(1024,1280,3)); 
app.UIAxes.XLim = [0,1280]; 
app.UIAxes.YLim = [0,1024]; 
app.UIAxes.XTick = []; 
app.UIAxes.YTick = []; 
pbaspect(app.UIAxes,[1280,1024,1]); 
preview(app.vid,hImage);

Now, in a different Callback, I want to gather an image from the actual live picture. Right now i am using the following Code:

asd= getdata(app.vid); 
save('path','asd'); 

Unfortunately get the following Error when calling:

Error using imaqdevice/getdata (line 154) OBJ is not running and no frames are available. 

Can somebody help me to solve my problem?

Answer 1

[Prabhan Purwar]

Hi,

Folllowing is the code and app design

classdef app1 < matlab.apps.AppBase

    % Properties that correspond to app components
    properties (Access = public)
        UIFigure  matlab.ui.Figure
        UIAxes    matlab.ui.control.UIAxes
        UIAxes2   matlab.ui.control.UIAxes
        Button    matlab.ui.control.Button
    end

    
    properties (Access = public)
        cam;
    end
    

    % Callbacks that handle component events
    methods (Access = private)

        % Code that executes after component creation
        function startupFcn(app)
            app.UIAxes2.Visible = 'off';
            evalin("base", 'clear cam');
            app.cam = webcam;
            frame = snapshot(app.cam);
            im = image(app.UIAxes, zeros(size(frame), 'uint8'));
            axis(app.UIAxes, 'image');
            preview(app.cam, im);
        end

        % Button pushed function: Button
        function ButtonPushed(app, event)
            img = snapshot(app.cam);
            image(app.UIAxes2, img);
            app.UIAxes2.Visible = 'off';
        end
    end

    % Component initialization
    methods (Access = private)

        % Create UIFigure and components
        function createComponents(app)

            % Create UIFigure and hide until all components are created
            app.UIFigure = uifigure('Visible', 'off');
            app.UIFigure.Position = [100 100 640 480];
            app.UIFigure.Name = 'UI Figure';

            % Create UIAxes
            app.UIAxes = uiaxes(app.UIFigure);
            title(app.UIAxes, 'Title')
            xlabel(app.UIAxes, 'X')
            ylabel(app.UIAxes, 'Y')
            app.UIAxes.Position = [26 270 300 185];

            % Create UIAxes2
            app.UIAxes2 = uiaxes(app.UIFigure);
            title(app.UIAxes2, 'Title')
            xlabel(app.UIAxes2, 'X')
            ylabel(app.UIAxes2, 'Y')
            app.UIAxes2.Position = [25 43 300 185];

            % Create Button
            app.Button = uibutton(app.UIFigure, 'push');
            app.Button.ButtonPushedFcn = createCallbackFcn(app, @ButtonPushed, true);
            app.Button.Position = [447 249 100 22];

            % Show the figure after all components are created
            app.UIFigure.Visible = 'on';
        end
    end

    % App creation and deletion
    methods (Access = public)

        % Construct app
        function app = app1

            % Create UIFigure and components
            createComponents(app)

            % Register the app with App Designer
            registerApp(app, app.UIFigure)

            % Execute the startup function
            runStartupFcn(app, @startupFcn)

            if nargout == 0
                clear app
            end
        end

        % Code that executes before app deletion
        function delete(app)

            % Delete UIFigure when app is deleted
            delete(app.UIFigure)
        end
    end
end

Error you are facing instantiates that the code is not able to access the camera object at that instant.

Hope it helps!!

[Gireesh Hosakoppa]

do you have made any videos of this