Master Thesis - Department of Computer Science
Master Thesis - Department of Computer Science
Master Thesis - Department of Computer Science
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for a face. This was illustrated by experimentation in [94] where the reconstruction<br />
<strong>of</strong> a face image from subbands upto a certain level, below that <strong>of</strong> the original face<br />
image at the root, provides better performance for face recognition. It is thus <strong>of</strong>ten<br />
necessary to eliminate the details for the representation <strong>of</strong> a face, and in such cases<br />
the subband face is obtained by partial reconstruction. In this chapter, we provide an<br />
algorithm to obtain optimum subject-specific subbands on the basis <strong>of</strong> minimization<br />
<strong>of</strong> four different criteria. Results <strong>of</strong> our experimentation presented in section 3.4<br />
will validate a hypothesis that “subband face representation provides efficient face<br />
recognition”. Our approach is different from that suggested in [36, 40, 26, 140] where<br />
the individual subbands <strong>of</strong> the face image have been used as features separately<br />
or unified by subspace analysis techniques for face recognition. None <strong>of</strong> the past<br />
approaches deals with a method to reconstruct a subband face using IDWT (synthesis<br />
filter bank).<br />
Face image<br />
Subband faces<br />
LSA (Linear Subspace Analysis):<br />
Subbands<br />
DWT IDWT<br />
LSA<br />
PCA, LDA, 2D−PCA, 2D−LDA, DCV.<br />
(a)<br />
Features<br />
(b)<br />
Subband selection<br />
Find nearest<br />
neighbor<br />
Templates from<br />
training set<br />
Subband face<br />
Distance<br />
Figure 3.1: (a) Block diagram for generating subband face. The face image is decom-<br />
posed using Discrete Wavelet Transform (DWT) into subbands. Selected subbands<br />
are used to reconstruct the subband face using inverse DWT. (b) Subband faces are<br />
projected onto a lower dimension featurespace using PCA or LDA (or their variants)<br />
and matched using the nearest neighbor strategy.<br />
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