I am trying to track small object in videos using LK but the problem is, some time the object does not appear in the frames !

How can I track an object that does not appear in few frames ?? how can I approximate it is place automatically ,,,

I am trying to find the object using Optical flow LK ... but this technique lost when my object does not appear

Any suggestion ideas ???


1 Answer 1


The short answer is: use your optical flow algorithm to get the best-fit warping of some number of previous images into your current image. Then assume that your object is moving on a line through the images, and do some kind of robust best-fit to that line. When the object reappears it is more likely to be near the predicted projection of the line than not.

You didn't give enough specifics in your question to really say more than that.

I assume by "LK" you mean "the Lucas-Kanade optical flow algorithm?" But what are you really doing? Are you taking image pyramids of each image and then doing multiple iterations of warping at each level of the pyramid? Are you really doing the simplest form of Lucas-Kanade or are you actually doing one of the varieties of Kanade-Lucas-Tomasi where you are concentrating on "corners"?

What is your description of an "object"? Is it really just a "feature" (a corner point) or a small set of features?

You may need to use a more accurate and robust optical flow algorithm. For example, some variation that does dense estimation (rather than the sparse estimation done by Lucas-Kanade) and that uses more robust distance metrics than least squares.

For example:

Secrets of optical flow estimation and their principles Sun, D., Roth, S., and Black, M. J., IEEE Conf. on Computer Vision and Pattern Recog., CVPR, June 2010.

  • $\begingroup$ Hi.. Thanks for your replay ... Actually I am trying to find a small object in X-ray images which is epiglottis !!! ... I wanna track it is movement from videos of x-ray images.. I am taking input from the user which is the place of the tip of the epiglottis ... then I wanna find it in all other frames ... yes I am using Optical Flow LK as you said ... but this algorithm cannot find the object when it does not appear in some frames !!! ... Also I do not know how can I approximate the place ! ... $\endgroup$
    – seereen
    May 18, 2013 at 21:09
  • $\begingroup$ Epiglottis does not have any special feature !! ... not corner of edge or anything ... but optical flow find it in the first half of the movement because it is still appear ,,, $\endgroup$
    – seereen
    May 18, 2013 at 21:13
  • $\begingroup$ how can I approximate the place ? ... any help will b so appreciated :D $\endgroup$
    – seereen
    May 18, 2013 at 21:13
  • $\begingroup$ Now I'm confused. How is LK "finding" the tip of the epiglottis in the frames where it is visible? All LK tells you is what parts of the image are moving. $\endgroup$ May 19, 2013 at 1:43
  • $\begingroup$ I give LK the location of the tip only to find it in next frame .... it is working with me but only when the tip is visible .... $\endgroup$
    – seereen
    May 19, 2013 at 1:52

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