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Master Thesis - Department of Computer Science

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Prior to Matching<br />

Sensor Level Feature Level<br />

Abstract Level<br />

(i) Majority Voting<br />

(ii) Behavior Knowledge<br />

Space<br />

(iii) AND Rule<br />

(iv) OR Rule<br />

(i) Weighted Summation<br />

(ii) Concatenation<br />

Information Fusion in Biometrics<br />

(i) Sum Rule<br />

(ii) Product Rule<br />

(iii) Max Rule<br />

(iv) Min Rule<br />

(v) Weighted Sum<br />

Combination<br />

Approach<br />

Dynamic<br />

Classifier<br />

Selection<br />

After matching<br />

Rank Level Measurement Level<br />

(i) Highest Rank<br />

(ii) Borda Count<br />

(iii) Logistic<br />

Regression<br />

Class−conscious<br />

Approach<br />

Class−indifferent<br />

Approach<br />

(i) Decision Template (DT)<br />

(ii) Demster−Shafer (DS)<br />

(iii) Neural Network (NN)<br />

(i) k−NN<br />

(vi) Logistic Classifier (LOG)<br />

Decision<br />

Level<br />

Fusion<br />

(ii) Decision Trees<br />

(iii) SVM<br />

Classification<br />

Approach<br />

(iv) Linear Discriminant Classifier (LDC)<br />

(v) Quadratic Discriminant Classifier (QDC)<br />

Figure 2.11: Summary <strong>of</strong> approaches to information fusion in biometric systems.<br />

For example, the face images obtained from several cameras can be combined<br />

to form a 3D model <strong>of</strong> the face.<br />

• Feature level: Feature level fusion refers to combining different feature vec-<br />

tors that are obtained from one <strong>of</strong> the following sources: multiple sensors for<br />

the same biometric trait, multiple instances <strong>of</strong> the same biometric trait, multi-<br />

ple units <strong>of</strong> the same biometric trait or multiple biometric traits. When feature<br />

vectors are homogeneous, a single resultant feature vector can be calculated as a<br />

weighted average <strong>of</strong> the individual feature vectors. In case <strong>of</strong> non-homogeneous<br />

features, we can concatenate them to form a single feature vector which is not<br />

possible for incompatible feature sets. Attempts by Kumar et al. [66] in com-<br />

bining palmprint and hand-geometry features and by Ross and Govindarajan<br />

37

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