Feature Extraction and Image Processing

Flexible shape extraction (snakes and other techniques) 235

linearisation of the coverage of the space in between the two contours, but these can make

implementation much more complex.

The approach again uses regularisation, where the snake energy is a discrete form to

Equation 6.40 so the energy at a snake point (unlike earlier formulations, e.g. Equation

6.11) is

E(v

i

) = −E

int

(v

i

) + (1 – −)E

ext

(v

i

) (6.43)

where the internal energy is formulated as

E

i

i

i

i

ii

int

+1 –1

+1 –1

2

() =

| – 2 + |

| – |

v

vvv

vv

(6.44)

The numerator expresses the curvature, seen earlier in the Greedy formulation. It is scaled

by a factor that ensures the contour is scale invariant with ...