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pythonopencvopticalflow
rishran
rishran

Reputation: 660

OpenCV running optical flow on particular rectangles

I am using OpenCV's Optical Flow module. I understand the examples in the documentation but those take the entire image and then get the optical flow over the image.

I only want to pass it over some parts of an image. Is it possible to do that? If yes, how do I go about it?

Thanks!

Upvotes: 0

Views: 596

Answers (1)

JDBones
JDBones

Reputation: 495

Yes, it's possible. cv2.calcOpticalFlowPyrLK() will be the optical flow function you need. Before you make that function call, you will have to create an image mask. I did a similar project, but in C++, though I can outline the steps for you:

  • Create an empty matrix with same width and height of your images
  • Using the points from your ROI, create a shape out of it (I did mine using cv2.fillPoly()) and fill the inside of the shape with white (Your image mask should only be comprised of black and white color)
  • If you are planning on using corners as features, then call cv2.goodFeaturesToTrack() and pass in the mask you've made as one of its arguments.
  • If you're using the Feature2D module to detect features, you can use the same mask to only extract the features in that masked area.
  • By this step, you should now have a collection of features/points that are only within the bounds of the shape! Call the optical flow function and then process the results.

I hope that helps.

Upvotes: 1

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