can't understand the cause of this error, trying to crop multi blobs in one image

Question

bay rem 2016-2-1

0
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https://ww2.mathworks.cn/matlabcentral/answers/266038-can-t-understand-the-cause-of-this-error-trying-to-crop-multi-blobs-in-one-image

编辑： Walter Roberson 2016-2-1

hello, i'm working with video motion, here it can be the case where we found many object mobile, i used blobAnalysis to delimited them, i calcul for each one it variance, i used this code but an error appeared, can anyone help me please:

foregroundDetector = vision.ForegroundDetector(*....);
videoReader = vision.VideoFileReader('*.avi',...
    'VideoOutputDataType','uint8');
J=0;
i=0;
while ~isDone(videoReader);
    J=J+1
    frameRGB = step(videoReader); % read the next video frame
    foreground = step(foregroundDetector, frameRGB);
blobAnalysis = vision.BlobAnalysis('BoundingBoxOutputPort', true, ...
    'AreaOutputPort', false, 'CentroidOutputPort', false, ...
    'MinimumBlobArea', 1700,'MaximumCount',2);
bbox = step(blobAnalysis, foreground);
result = insertShape(frameRGB, 'Rectangle', bbox, 'Color', 'green');
num = size(bbox,1);
    if J>=1;
      if num>1
      for i=1: num
      croppedImage = frameRGB(bbox(i, 2):bbox(i, 2)+bbox(i, 4), bbox(i, 1):bbox(i, 1)+bbox(i, 3), :);
      blobVariance(i) = var(double(croppedImage(:)))
    end
result = insertShape(frameRGB, 'Rectangle', bbox, 'Color', 'red');
result = insertText(result, [10 10], numperso, 'BoxOpacity', 1, ...
    'FontSize', 14);
figure(1); imshow(result);
blobVariance=[];
croppedImage=[];
    end
end
  end

end and the error is:

Index exceeds matrix dimensions.
Error in MaxvariancecorriG (line *)
 croppedImage = frameRGB(bbox(i, 2):bbox(i, 2)+bbox(i, 4), bbox(i, 1):bbox(i, 1)+bbox(i, 3),
 :);

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Stefan Raab 2016-2-1

Hey bay rem,

I am not familiar with the "step(videoPlayer)" function, but I suppose it results the frame as a matrix? Your error says, that you try to address an index which does not exist. Does "step" return a two dimensional array? Then you have too much indices in the "croppedImage = ..." command.

Kind regards, Stefan

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Answer 1

Walter Roberson 2016-2-1

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/266038-can-t-understand-the-cause-of-this-error-trying-to-crop-multi-blobs-in-one-image#answer_208070

编辑：Walter Roberson 2016-2-1

在 MATLAB Online 中打开

   croppedImage = frameRGB(bbox(i, 2):bbox(i, 2)+bbox(i, 4)-1, bbox(i, 1):bbox(i, 1)+bbox(i, 3)-1,:);

Remember, a width of 1 would mean that you should end at the same pixel, so your endpoint would be 0 further on from where you are. A width of 2 would mean you would end at the next pixel, so your endpoint would be 1 further on from where you are. And so on: a width of N requires a last index of N-1 beyond where you are.