How to live stream on 2 axes from the same camera?

I'm building app on appdesigner in which I try to stream live videos from the same camera on 2 axes

with the following code:

classdef imApp < matlab.apps.AppBase

% Properties that correspond to app components

properties (Access = public)

UIFigure matlab.ui.Figure

StartButton matlab.ui.control.Button

UIAxes1 matlab.ui.control.UIAxes

UIAxes2 matlab.ui.control.UIAxes

end

properties (Access = private)

cam; % Description

end

% Callbacks that handle component events

methods (Access = private)

% Button pushed function: StartButton

function StartButtonPushed(app, event)

app.cam = webcam;

frame = snapshot(app.cam);

im1 = image(app.UIAxes1, zeros(size(frame),'uint8'));

im2 = image(app.UIAxes2, zeros(size(frame),'uint8'));

axis(app.UIAxes1,'image');

axis(app.UIAxes2,'image');

preview(app.cam,im1);

preview(app.cam,im2);

% pause;

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 = [100 100 800 800];

app.UIFigure.Name = 'UI Figure';

% Create StartButton

app.StartButton = uibutton(app.UIFigure, 'push');

app.StartButton.ButtonPushedFcn = createCallbackFcn(app, @StartButtonPushed, true);

app.StartButton.Position = [271 430 100 22];

app.StartButton.Text = 'Start';

% Create UIAxes

app.UIAxes1 = uiaxes(app.UIFigure);

title(app.UIAxes1, 'Title')

xlabel(app.UIAxes1, 'X')

ylabel(app.UIAxes1, 'Y')

app.UIAxes1.Position = [51 35 511 363];

%Create second axis

app.UIAxes2 = uiaxes(app.UIFigure);

title(app.UIAxes2, 'Title')

xlabel(app.UIAxes2, 'X')

ylabel(app.UIAxes2, 'Y')

app.UIAxes2.Position = [600 35 511 363];

% 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 = untitled

% Create UIFigure and components

createComponents(app)

% Register the app with App Designer

registerApp(app, app.UIFigure)

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

Unfortunately, it only stream on one axe and not both on the same time, how to make it stream the same video on the same time on both axes ?

Answer 1

[Nivedita]

Hi Guy Hanzon!

I understand that you are trying to stream live video from the same camera at the same time on two different axes in your app.

You can achieve it by modifying your “ButtonPushed” callback function in the following manner:

% Button pushed function: StartButton
        function StartButtonPushed(app, event)
            app.cam = webcam;
            frame = snapshot(app.cam);

            % Create image objects for each axis
            im1 = image(app.UIAxes1, zeros(size(frame), 'uint8'));
            axis(app.UIAxes1, 'image');

            im2 = image(app.UIAxes2, zeros(size(frame), 'uint8'));
            axis(app.UIAxes2, 'image');
            
            % Start streaming the video
            while true
                frame = snapshot(app.cam);
                set(im1, 'CData', frame);
                set(im2, 'CData', frame);
                drawnow;
            end
        end

• The “while” loop continuously captures frames from the webcam and updates the image data for both the image objects (“im1” and “im2”).
• The “set” function is used to update the image data with the captured frame.
• The “drawnow” function updates the display and ensures that the image is shown on the axes immediately.

For more information on “while” loop, and “set” and “drawnow” functions, refer to the following documentation links:

• while: https://www.mathworks.com/help/matlab/ref/while.html
• set: https://www.mathworks.com/help/matlab/ref/set.html
• drawnow: https://www.mathworks.com/help/matlab/ref/drawnow.html

I hope this helps!

Regards,

Nivedita.