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Face Detection and Modeling for Recognition - Biometrics Research ...

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segment. The other term favors an upright face, <strong>and</strong> is a projection of a vector ⃗v 2<br />

(from the mouth to the midpoint of the two eyes) along the vertical axis ( ⃗u 2 ) of the<br />

image plane. The exponential function, shown in Fig. 3.14, is designed such that the<br />

attenuation has the maximal value of 1 when θ 1 = θ 2 = 0 ◦ (i.e., when eyes <strong>and</strong> mouth<br />

<strong>for</strong>m a letter “T” or equivalently the face is upright), <strong>and</strong> it decreases to below 0.5<br />

at θ 1 = θ 2 = 25 ◦ . The quality of face boundary, q(i, j, k), can be directly obtained<br />

from the votes received by the best elliptical face boundary in the Hough trans<strong>for</strong>m.<br />

Eye i<br />

V 2<br />

u 1<br />

Eye j<br />

u 2<br />

1<br />

V 1<br />

2<br />

1<br />

Mouth k<br />

Figure 3.13. Geometry of an eye-mouth triangle, where ⃗v 1 = −⃗v 2 ; unit vectors ⃗u 1 <strong>and</strong><br />

⃗u 2 are perpendicular to the interocular segment <strong>and</strong> the horizontal axis, respectively.<br />

Figure 3.14. Attenuation term, e −3(1−cos2 (θ r(i,j,k))) , plotted as a function of the angle<br />

θ r (in degrees) has a maximal value of 1 at θ r = 0 ◦ , <strong>and</strong> a value of 0.5 at θ r = 25 ◦ .<br />

81

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