how to draw an updating rectangle object on a video stream ?

Hi there,

I am beginninger of matlab. I tried myCameraGUI example which build up a simple camera preview inferface. My question is I cannot find a way to draw a updating rectangle object on the top of streamed video. I do have tried many times, but fail in the end. Does anyone know how to do that? Any direction, webpage, or even a function would be appreciated. Thank you.

Steven

Answer 1

[Image Analyst]

It's possible to have graphics in the overlay above your live video. Did you call the preview() function to get live video, and then call plot() to plot your box?

[Steven]

No, I used start(handles.video) to play the view. and then I run this bit of code to initial and updating the mark

    DELAY = 0.025;
    numPoints = 600;

    %# create data
    x = linspace(0,10,numPoints);
    y = log(x);

    %# create moving point + coords text
    hLine = line('XData',x(1), 'YData',y(1), 'Color','r', ...
        'Marker','o', 'MarkerSize',6, 'LineWidth',2);

    set(hLine,'Parent',handles.cameraAxes);           % set ploting axes
    %# infinite loop
    i = 1;                                       %# index
    flag = 1;
    while flag    
        %# update point & text
        set(hLine, 'XData',x(i), 'YData',y(i))        
        drawnow                                  %# force refresh
        pause(DELAY)                           %# slow down animation

        i = rem(i+1,numPoints)+1;                %# circular increment
    end

Matlab returns an error when executing set(hLine, 'XData',x(i), 'YData',y(i)). And I don't know what goes wrong

[Image Analyst]

You need two x and two y, not one. Try calling line just like this

axes(handles.cameraAxes);
hold on;
line([x1 x2], [y1 y2]);

[Steven]

Could I ask you a question further? Say I'd like to process the input video frame by frame, and base on each frame that I get from the source camera I calculate the box and then update the box that I originally ploted on the video, what is best way of doing this in terms of system performance? Could you please recommand me a few functions that could do this. thanks a lot