[Insight-users] Motion Estimation, urgent help

[Luis Ibanez]

Hi Jayant,

The only LevelSet filter in ITK that requires
seed points is the FastMarching ImageFilter.

ShapeDetection and GeodesicActiveContours
use an initial level set. (The examples in
the software guide use a FastMarching filter
in order to provide this initialization, but
this is just one among many possible options.)

CannyEdgeDetectionLevelSet uses an input
image and computes from it the Canny edges
then attracts the zero set to the Canny edges.

ThresholdLevelSet use two thresholds to binarize
an input image and then use the edges as attractors
for the zero set.

Do you need this motion tracking to go fast ?
let's say at video rates ? 30Hz ?, 10 Hz ?


How big are your images ?
regular video like 640 x 480 ?

If you do an initial segmentation in one of the
first frames, you could take advantage of the
fact that most ITK level set filters use narrow
banding and therefore you could use the current
narrow band after convergence in one image in
order to follow to the next frame. Then use the
evolution of the Narrow band as output of the
motion estimation.

You could also modify the DemonsDeformable
registration in order to compute displacement
vectors between two consecutive frames.  Demons
is based on the concept of optical flow that is
commonly used in motion tracking and video
compression.  Note that this may require some
programming effort on your part.

Do you know the shape of the object that you expect
to track ? or is this just a motion detection
system like the ones used for tele-surveillance ?

If you know something about the shapes of the moving
objects you could also explore the use of SpatialObjects
to-Image registration, since by registering a
SpatialObject shape to the subject that you want
to track as seen in the first frame, you could then
use this position as initialization for registering
the same shape against frame 2, then the resulting
value will be used for registering againg frame 3
and so on.  The SpatialObject registration will
probably be the fastest option (at run time) since
a minimum number of image pixels need to be probed.
Note that this technique has been used in ITK for
image guided surgery.


Regards,


    Luis


----------------------
Jayant Chauhan wrote:

> Hey Fellas
> I am working on a project on Motion estimation and tracking, following 
> the works of Nikos Paragios and Denise Ritchie, using Geodesic Active 
> Regions and Level Set Methods. Has anyone worked on this ??!! Please let 
> me know. My problem is that, since we have a sequence of frames, we use 
> the difference image between 2 consecutive frames, and start of with the 
> initial contour to be the image boundary, and we propagate it inwards 
> bla...bla...blah.  As in chapter 9 of ITK guide, all implemented filters 
> need seed points. But in my case we have to do without the seed points, 
> they are not required. Also my speed function is a funtion of the 
> curvature as well as the gradient of the difference image. Can anyone 
> please help me out with it, I am completely new
> with ITK.
> 
> I have to implement this and not much time, most time spent of the 
> mathematics and formulating a scheme of my own.
> 
> with regards
> 
> Jayant Chauhan
> 
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