Can vision.For​egroundDet​ector work on GUI

Hi, Can I use GUI to display foreground from vision.ForegroundDetector? By using the same method I can extract the foreground. But in the GUI I can't display the foreground. Please help, thanks

[Image Analyst]

Why not? Did you call imshow()?

[Leona Chan]

Yes, I had. I can display the frame, but foreground cannot. These are some pieces of code

function playCallback(hObject,~,videoSrc,hAxes)

while strcmp(hObject.String, 'Pause') && ~isDone(videoSrc)

[frame,result] = getAndProcessFrame(videoSrc);

showFrameOnAxis(hAxes.axis1, frame);

showFrameOnAxis(hAxes.axis2, result);

end

function [frame,foreground] = getAndProcessFrame(videoSrc)

foregroundDetector = vision.ForegroundDetector('NumGaussians', 4, ... 'NumTrainingFrames', 60);

frame = step(videoSrc);

foreground = step(foregroundDetector, frame); end

[Jiro Doke]

What do you mean by "you can't display the foreground"? Do you get an error? Does it show something but not what you expect? Is it possible that for the frame input, no foreground was detected? What exactly is the situation?

Answer 1

[Leona Chan]

As above code, showFrameOnAxis(hAxes.axis1, frame); showFrameOnAxis(hAxes.axis2, foreground); The frame can show in both axis1 or axis2, but put foreground either axis1 or axis2 also nothing to display.

[Jiro Doke]

(If possible, please move this to the Comments section above, since this is the "Answers" section)

Please be a bit more clear. When you say "nothing to display", does it show all black? All white? Something else? Do you see error messages in the Command Window?

[Leona Chan]

All black and no message in the command window

[Jiro Doke]

That probably means that the algorithm didn't detect any foreground. Detected foreground would show up in white (in the black&white image).

[Leona Chan]

But I can extract the foreground by the same method.

[Jiro Doke]

"Same method" as in using foregroundDetector in a loop with video frames?

I can't say for certain, but you may need to take the vision.ForegroundDetector initialization outside of the "loop". If I remember correctly, the detector uses past frames to estimate the background. Currently, in your snippet of code, you are recreating the detector for each frame, thus clearing the past frames from its algorithm. Just using your code snippet, you may need to change to something like this.

function playCallback(hObject,~,videoSrc,hAxes)
    foregroundDetector = vision.ForegroundDetector('NumGaussians', 4, ...
                 'NumTrainingFrames', 60);
    while strcmp(hObject.String, 'Pause') && ~isDone(videoSrc)
        [frame,result] = getAndProcessFrame(videoSrc,foregroundDetector);
        showFrameOnAxis(hAxes.axis1, frame);
        showFrameOnAxis(hAxes.axis2, result);
    end
end

function [frame,foreground] = getAndProcessFrame(videoSrc,foregroundDetector)
    frame = step(videoSrc);
    foreground = step(foregroundDetector, frame);
end

[Leona Chan]

Yes, work now, thank you very much