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Method for Occlusions Preserving Surfaces and Occlusions Breaking Surfaces [1, 6]

Image Segmentation
The image range can be segmented by extracting depth discontinuities either across each coordinate axis [1], or between neighbouring fitted 3D surfaces [6]. The case of depth discontinuities is represented in figure 3, while the case of 3D surfaces is represented in figure 4.

The extracted surfaces are further segmented by analysing their surface orientation. This process is called fold edge detection. The result of this detection is shown in figure 5. The right-hand figure shows that a fold edge detection leads to a more accurate detection.

  figure73
Figure 3: A Range image (left) and corresponding extracted regions after labelling (right).

  figure84
Figure 4: The first segmentation.

  figure95
Figure 5: An intensity image (left) and its corresponding range image (center-left). The same image after depth discontinuity processing (center-right) and additional partitioned using fold edges (right).

Surface Fitting
The extracted surfaces are then fitted by parametric surface shapes in order to obtain good comparative measures. Experiments have shown that planes, cylinders and spheres are usually sufficient to describe most of the simple surfaces in architectural scenes. The following table shows the parameters associated with each surface type.

Surface type Description
Planar surface normal tex2html_wrap_inline586
displacement disp
Cylindrical point on axis p
(circular) unit vector of axis tex2html_wrap_inline592
radius r
Spherical centre c
radius r

For two surfaces to be contiguous, they must be first of the same type. The surface parameters introduced above can be used for comparison. The following table gives the parameters and the thresholds used for determining whether two surfaces match or not.

Surface type Requirements for matching
Plane tex2html_wrap_inline600
tex2html_wrap_inline602
Cylinder tex2html_wrap_inline604
tex2html_wrap_inline606
tex2html_wrap_inline608
tex2html_wrap_inline610
Sphere tex2html_wrap_inline612
tex2html_wrap_inline610

next up previous
Next: Method for Occlusions Breaking Up: Occlusion Understanding Previous: Occlusion Understanding

Bob Fisher
Thu Jan 17 16:45:14 GMT 2002