readFrame to slow, is there a faster way?

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david csernay 2017-11-18

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/367828-readframe-to-slow-is-there-a-faster-way

评论： david csernay 2017-11-20

Hello

I want to "cut out" objects that are placed in front of a green screen in real time, and replace the background with a video.

The object extraction itself works fine (tested with a simple image as background).

Then i tried to implement a background video with 'readFrame', but the background video runs in slow motion (see files attached), plus the live stream gets laggy too.

Is there a faster way to acquire single video frames and process them?

Thanks for any help!

function example1
    % webcam
    cam = videoinput('winvideo',1);
    % get background image
    img1 = getsnapshot(cam);
    % video objekt
    vidobj1 = VideoReader('Testvideo.mp4');
      % background
      background = readFrame(vidobj1,'native');
      background = imresize(background, [size(img1, 1), size(img1, 2)]);
      img = imshow(background,'InitialMagnification','fit');
      % Set a custom preview function
      setappdata(img,'UpdatePreviewWindowFcn',@mypreview_fcn);
      % Call preview with the custom image
      preview(cam,img);
      function mypreview_fcn(obj,event,himage)
          % receive the image in event.Data
          foreground = event.Data;
          background = readFrame(vidobj1,'native');
          [overlayed,a] = greenScreen(foreground, background);
          % Display
          set(img, 'CData', overlayed);
      end
  end

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Answer 1

Walter Roberson 2017-11-18

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https://ww2.mathworks.cn/matlabcentral/answers/367828-readframe-to-slow-is-there-a-faster-way#answer_291874

The Computer Vision reader should be faster; see https://www.mathworks.com/help/vision/ref/vision.videofilereader-system-object.html

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Walter Roberson 2017-11-20

There is im2double instead of im2single() . Without testing it is difficult to say which would lead to faster code.

david csernay 2017-11-20

Ok, with im2double the extraction works, but the video is still slow.

How would you approach the problem? Is there another way for object extraction? Actually, i would like to keep the green screen method, because of its good extraction results.

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