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Master Thesis - Department of Computer Science

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(a) (b)<br />

Figure A.2: Input fingerprint images.<br />

(a) (b)<br />

Figure A.3: Normalized images <strong>of</strong> two input fingerprints shown in Fig. A.2.<br />

where M0 and V AR0 are the desired mean and variance values, respectively. Nor-<br />

malization is a pixel-wise operation. It does not change the clarity <strong>of</strong> the ridge and<br />

valley structures. It reduces the variations in gray-level values along ridges and val-<br />

leys, which facilitates the subsequent processing steps. Fig A.3 shows the result <strong>of</strong><br />

normalization on two different fingerprint images shown in Fig A.2.<br />

A.1.3 Orientation Image<br />

The orientation image represents an intrinsic property <strong>of</strong> the fingerprint images and<br />

defines invariant coordinates for ridges and valleys in a local neighborhood. By view-<br />

ing a fingerprint image as an orientated texture, a least mean square orientation<br />

estimation algorithm is given below:<br />

1. Divide G into blocks <strong>of</strong> size W × W (16 × 16).<br />

125

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