How can I find the starting point of the flows in optical flow?

I am performing smoke detection using optical flow. How can we find the starting point of acting?

vidReader = VideoReader('test1.avi', 'CurrentTime', 1);

% opticFlowLK = opticalFlowLK('NoiseThreshold', 0.009);
% opticFlowFarneback = opticalFlowFarneback;
opticFlow = opticalFlowHS;
opticFlowLKDoG = opticalFlowLKDoG('NumFrames', 3);

while hasFrame(vidReader)
    frameRGB = readFrame(vidReader);
    frameGray = rgb2gray(frameRGB);

      flow = estimateFlow(opticFlow, frameGray); 
      m = flow.Magnitude;

      figure(1);
      imshow(frameRGB);
      hold on
      plot(flow,'DecimationFactor',[5 5],'ScaleFactor', 100);
      hold off

      %pause(0.1);
  end

[KSSV]

Any pictorial example?

[Jae Min Lee]

I uploaded a picture.

[KSSV]

How did you draw those blur arrows

[Jae Min Lee]

I uploaded the source code.

Answer 1

[Bjorn Gustavsson]

Well, in principle you can determine sources and sinks of a flow by looking at its divergence. Regions with divergence larger than zero are sources, smaller than zero sinks. This is valid for a 3-D flow in 3-D, or a 2-D flow in 2-D - you, however, have 2-D images of 3-D flow so extra caution has to be taken. But since we're already on our way - you might get something out of trying to look at divergences of your optical flow, you most likely should do whole lot of low-pass filterings on the divergence and perhaps the flow-vectors.

If that fails you could have a look at Helmholtz decomposition and further on, if you can get some more robust estimates.

Let us know how you proceedings go. Good luck!

HTH

[Jae Min Lee]

Thank you very much!

Answer 2

[KSSV]

Check this variable flow. This should be having your location coordinates, from here you can pick the initial point.

[Jae Min Lee]

Thank you for your reply. But I don't understand. Can you give me a little detail?

[KSSV]

As I don't have data in hand....I don't know how the flow variable is.