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Master Thesis - Department of Computer Science

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3.1 (a) Block diagram for generating subband face. The face image is de-<br />

composed using Discrete Wavelet Transform (DWT) into subbands.<br />

Selected subbands are used to reconstruct the subband face using in-<br />

verse DWT. (b) Subband faces are projected onto a lower dimension<br />

featurespace using PCA or LDA (or their variants) and matched using<br />

the nearest neighbor strategy. . . . . . . . . . . . . . . . . . . . . . . 47<br />

3.2 Two dimensional discrete wavelet transform (DWT) for an image: The<br />

low pass filter h(.) and the high pass filter g(.) are applied along the<br />

rows initially followed by downsampling by a factor <strong>of</strong> two. This is<br />

followed by filtering using h(.) and g(.) along the columns and down-<br />

sampled by factor <strong>of</strong> two. . . . . . . . . . . . . . . . . . . . . . . . . 49<br />

3.3 (a) Original face, (b) the level-1 wavelet decomposition <strong>of</strong> the face<br />

image into subbands A, H (top) and V , D (bottom) and (c) level-<br />

3 dyadic wavelet decomposition. All subband signals are normalized<br />

individually. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50<br />

3.4 Two dimensional inverse discrete wavelet transform (IDWT) for an<br />

image. The rows are initially upsampled by factor <strong>of</strong> two and filtered<br />

using low pass h(.) and high pass g(.) filters. This is followed by upsam-<br />

pling along columns by a factor <strong>of</strong> two and applying the low pass h(.)<br />

and high pass g(.) filters along the columns to get the reconstructed<br />

image. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51<br />

3.5 Reconstruction <strong>of</strong> a subband face using two dimensional Inverse Dis-<br />

crete Wavelet Transform (IDWT) from level-2 subbands. The approx-<br />

imation at level-2, LL2, is suppressed (by replacing with zeros) while<br />

reconstructing the approximation at level-1, LL1. This is further used<br />

to generate the subband face at level-0. . . . . . . . . . . . . . . . . . 52<br />

3.6 (a), (b), (c): Typical examples <strong>of</strong> sample face images from the Yale,<br />

PIE and ORL face databases. The respective subband faces (a1-c1),<br />

(a2-c2) and (a3-c3) with the approximations at level-4, level-5 and<br />

level-6 suppressed. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53<br />

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