Wierd behaviour of 'bwareafilt' & also what algorithm does it use ?

If anyone has answer of any of following , please help urgently :)

1. What is the algorithm that 'bwareafilt' uses ?
2. Wierd Behaviour : When the input matrix is totally black then i get following error :-(Actually i am using this function to take snapshots from webcam but when i block my webcam totally, then i get the following error )

    Error using bwpropfilt (line 73)
    Internal error: p must be positive.

    Error in bwareafilt (line 33)
    bw2 = bwpropfilt(bw, 'area', p, direction, conn);

    Error in colour_reception (line 95)
    Iz=bwareafilt(b,1);

[Walter Roberson]

http://www.mathworks.com/matlabcentral/answers/29922-why-your-question-is-not-urgent-or-an-emergency

Answer 1

[Image Analyst]

It most likely calls regionprops() then sorts based on area, then uses indexing or ismember() to extract only the blobs you specified.

Please attach your binary image b. Put it in a .mat file so the class and everything else doesn't change at all. Otherwise, if we don't get "b", we can't investigate your problem. But the way, just checking, b IS a binary image isn't it - it's not a gray scale or color image , right?

It could also be helpful to see your complete image segmentation algorithm so that I know how binary (logical) image "b" was created from the true color RGB image from the webcam.

[monu vdvdsag]

http://ideone.com/vD7DXU Please put your palm touching webcam (so as to cover it fully) & then play this script , you will get error. If u dont cover webcam fully , magically no error anywhere!

[Image Analyst]

I guess it's just a choice they made. What do you do if your user asks for the largest blob when the image is totally black/false/0 and there is not even a single blob. Do you return a black image, or do you throw an error. I guess they decided to throw an error.

Put it in a try catch

try
  b = bwfiltarea(b, 1);
catch
  message = sprintf('Warning: there are no blobs to return to you');
  uiwait(warndlg(message));
end