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In this section, we describe a contour based algorithm to estimate a
pose of the articulated object. This algorithm uses the definition of
the model, but does not use the values in the model so we can easily
change the target object without modifying the algorithm.
Each part in the model is taken up one by one and its rotation angles
are determined based on the overlap relationship between the contour
of the silhouette and that of the projected region on the image plane.
Suppose a set has the parts whose rotation angles have been
determined and a set has the parts whose parent part belongs
to . The rest parts belong to a set . At the beginning
only contains the root part and all other parts are in .
- Selection of the Part
Select a Part i in . If there is no part in , the
algorithm terminates. Make a new candidate-list for Part i. A
candidate in the candidate-list represents a possible pose of Part
i, and has at most three rotation angle values which are quantized
by a certain unit interval. The unit size defines the resolution of
the pose estimation. A candidate can not have values that make the
projected region of Part i stray out from the silhouette. If there
exist no candidates in the candidate-list, go to Step
3.
- Estimation of the angles
To find the best pose of Part i, the system measures the length of
the contour where the contour of the silhouette overlaps with that of
the projected region for each candidate in the candidate-list. The
candidate with the largest overlap is adopted as the estimated result.
The rotation angles are fixed to the values of the candidate, and then
it is removed from the candidate-list. Move Part i from to
, and the children of Part i in are moved to . Go to Step 1.
- Backtracking
Backtrack from Part i to the root part until Part j, which
keeps at least one candidate in the candidate-list, is found. Move all
of its children descendants into . For Part j,
execute the same algorithm as Step 2. Go to Step
1.
Since it is not clear what kind of criterion is necessary to select
the part in Step 1, our method here selects it
arbitrarily. We are currently investigating this problem.
Next: Experimental Results
Up: Contour Based Method
Previous: Model
Yoshinari Kameda
Thu Apr 3 22:11:48 JST 1997