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Master Thesis - Department of Computer Science

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maximum values <strong>of</strong> l and k (L and K, respectively) depend on original image size and<br />

the subspace method used.<br />

The terms Goat and Lamb originated from speaker verification [34] and then prop-<br />

agated in the field <strong>of</strong> biometry [107]. Goats are the group <strong>of</strong> subjects that are hard<br />

to authenticate and generate the majority <strong>of</strong> false rejects. The group <strong>of</strong> subjects<br />

that are easy to imitate and cause false acceptance are regarded as Lambs. Appro-<br />

priate subband for a person gathers all common intra-class detail features specific<br />

to a subject as well as eliminates the common inter-class structural features present<br />

across subjects. So, it can be stated that a proper subband face has the power to<br />

extract features that are invariant within a subject and at the same time discriminant<br />

across different subjects. Goatishness and labmishness measures for each person are<br />

calculated from the genuine and impostor distributions obtained from the confusion<br />

matrix on a validation set.<br />

Formally, let n and p be the number <strong>of</strong> samples per subject used for training and<br />

validation, respectively. The columns and rows <strong>of</strong> a confusion matrix correspond to<br />

the training and validation samples for different classes arranged sequentially. So a<br />

confusion matrix (CM) can be organized as follows,<br />

⎡<br />

m(11)(11) ⎢ . . . m(11)(1j) . . . m(11)(1n) . . . m(11)(ij) . . . m(11)(Cn)<br />

⎢ . . . . . . . . . . . . . . . . . . . . . . . . . . .<br />

⎢ m(1s)(11) . . . m(1s)(1j) . . . m(1s)(1n) . . . m(1s)(ij) . . . m(1s)(Cn)<br />

⎢ . . . . . . . . . . . . . . . . . . . . . . . . . . .<br />

⎢<br />

CM = ⎢ m(1p)(11) . . . m(1p)(1j) . . . m(1p)(1n) . . . m(1p)(ij) . . . m(1p)(Cn)<br />

⎢ . . . . . . . . . . . . . . . . . . . . . . . . . . .<br />

⎢ m(rs)(11) . . . m(rs)(1j) . . . m(rs)(1n) . . . m(rs)(ij) . . . m(rs)(Cn)<br />

⎢ . . . . . . . . . . . . . . . . . . . . . . . . . . .<br />

⎣<br />

m(Cp)(11) . . . m(Cp)(1j) . . . m(Cp)(1n) . . . m(Cp)(ij) . . . m(Cp)(Cn)<br />

(3.1)<br />

An element m(rs)(ij) represents the similarity measure (score value) between s th<br />

validation sample from class r and j th training sample from class i and takes value in<br />

the range <strong>of</strong> [0, 1]. Now the genuine and impostor score sets for class i, denoted as<br />

54<br />

⎤<br />

⎥<br />

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