Active Contours: The Application of Techniques from by Andrew Blake

By Andrew Blake

Active Contours bargains with the research of relocating photos - an issue of growing to be significance in the special effects undefined. particularly it truly is interested in figuring out, specifying and studying earlier versions of various energy and utilizing them to dynamic contours. Its objective is to increase and examine those modelling instruments extensive and inside a constant framework.

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Additional resources for Active Contours: The Application of Techniques from Graphics, Vision, Control Theory and Statistics to Visual Tracking of Shapes in Motion

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The practical upshot is that with B-splines the smoothness terms can be omitted, allowing a substantial reduction in the number of nodal variables required, and improving computational efficiency considerably. For this reason, the B-spline representation of curves is used throughout this book. Details are given in chapter 3. Robustness and stability Regularising terms in the dynamical equations are helpful to stabilise snakes but are rather restricted in their action. They represent very general constraints on shape, encouraging the snake to be short and smooth.

We take each span to have unit length. 2. It shows the simplest case in which the knots are evenly spaced and the joins between polynomials are regular - that is, as smooth as possible, having d - 2 continuous derivatives. The quadratic spline, for instance, has continuous gradie;nt in the regular case. (s) ... /', .... "'\ ' \ " ". 2: (top) A single quadratic B-spline basis function Bo(s). "Knots" at s =,0,1,2,3,4 mark transitions between polynomial segments of the function. (bottom) In the regular case which has evenly spaced knots (at integral values of s), each B-spline basis function is a translated copy of the previous one.

At a regular breakpoint (single knot), the degree of smoothness is at its maximal value, that is C d - 2 - continuity of all derivatives up to the (d - 2)th. At a double knot, however, continuity is reduced to C d - 3 and generally, continuity at a knot of multiplicity m is C d - m - 1 . 7 for the quadratic case. Once a double knot has been introduced into the basis, any constructed spline function generally loses one order of continuity at that breakpoint. 8 for an illustration. If a triple knot is introduced, the function becomes discontinuous, broken into two continuous pieces, one on each side of the knot.

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