Edited by author 10-08-2002 03:54 AM
Andrew: The paper says that 3 different approaches can be taken to choose the regions/segments:
1) Color Based segmentation
2) Egde based triangulation.
3) Point based triangulation.

However, only color based segmentation is used partly because it is easy to implement and party because it is reliable.

Color segmentation is a well studied field and usually we dont ask the question " how accurate it is" but "how much segmentation". Your question now becomes very pertinent and it indeed IS one of the primary aspects of the paper. The answer is : We want to "over-segment" the image by which I mean we would like to segment even regions which look homogeneous if possible. This ensures that even curved surfaces are modeled as piecewise planar ( just as in graphics most curved objects are composed of triangles which are planar) and we dont smooth out the curve by planar approximation.