Game Development Reference
In-Depth Information
1)
Approximating the camera geometry by some simpler model, such as
orthographic model (Lee & Huang, 1990), affine model (Tomasi & Kanade,
1991), or paraperspective model (Weinshall, 1993). A unification possibility
was discussed in Quan & Triggs (2000);
2)
A priori
information about the possible scene type (Xu, Terai & Shum,
2000) or certain properties of the relative poses of available 3-D scene
points (Boufama, Mohr & Veillon, 1993); or
3)
Constraints on the variation of the camera parameters. The constraints
employed can be represented by:
•
Restricted relative poses of all cameras, such as pure translation, pure
rotation, or planar motion (Moons, Gool, Proesmans & Pauwels,
1996).
•
Intrinsic parameters that have been revealed by passive calibration in
advance (Spet-sakis & Aloimonos, 1990) or by the first three views
on-line (Horn, 1991).
•
The assumption that all (or most) cameras have the same but unknown
intrinsic parameters (Triggs, 1998). In this case, Euclidean recon-
struction is achievable.
•
Varying intrinsic camera parameters subject to certain restrictions. In
Heyden & ÅströM (1999), some of the intrinsic parameters are
allowed to vary while others are fixed. Pollefeys et al. (1999) suggest
that one can neglect the skew parameter if one wants to vary all
intrinsic parameters.
Various combinations of the above-mentioned
a priori
information or con-
straints have also been investigated for self-calibration. For self-calibration, the
most frequently employed equation and concept are the Kruppa equation and the
absolute conic, respectively (Hartley & Zisserman, 2000).
Face Model Reconstruction and
Telepresence Applications
In this section, two applications that utilize the camera calibration results are
presented and analyzed. First, we will discuss 3-D face model reconstruction
and, second, a virtual telepresence application. For each application, the neces-
sary techniques involved are introduced and typical outcomes are presented. In
these two applications, general-purpose techniques are employed. However,
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