Method and device for determining a contour in a space of image parameter values
First Claim
1. Method for determining a contour in a space of image parameter values, comprising the following steps implemented on a computer:
- accessing a memory storing image parameter values in a space in the form of a matrix of pixel values;
defining a plurality of initial vertices being located on a seed contour in said space, said vertices being connected by edges to neighbouring vertices;
evaluating an energy function comprising an internal portion which is a function of a curvature at each of the vertices and an external portion determined by the variation of the image parameter values at the location of each of said vertices;
determining a final contour by continuously varying the position of the vertices till the energy function reaches a minimum, characterised in that,for each of the vertices the internal portion of the energy function is dependent on the angle between the edges at the respective vertex and in that the external portion of the energy function is determined by the variation of the image parameter values in a single direction that bisects the angle between the edges at the respective vertex.
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Abstract
In a space having image parameter values, a contour (10) is defined consisting of vertices (11, 12, 13) connected by edges (14, 15, 16). By variation of the position and number of the vertices as a function of the variation of image parameter values in the space, the contour (10) is determined to follow features in the density variation. The movement of vertices is restricted to a direction (Pi) perpendicular to the local direction (ti) of the contour (10). For smoothing the contour (10), an internal force or energy is defined at each of the vertices (11, 12, 13) which force or energy depends on the angle (ci) between the edges at the vertex, or of the variation of the angles along a sequence of adjacent vertices. A direct interaction between vertices is thereby avoided.
114 Citations
20 Claims
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1. Method for determining a contour in a space of image parameter values, comprising the following steps implemented on a computer:
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accessing a memory storing image parameter values in a space in the form of a matrix of pixel values; defining a plurality of initial vertices being located on a seed contour in said space, said vertices being connected by edges to neighbouring vertices; evaluating an energy function comprising an internal portion which is a function of a curvature at each of the vertices and an external portion determined by the variation of the image parameter values at the location of each of said vertices; determining a final contour by continuously varying the position of the vertices till the energy function reaches a minimum, characterised in that, for each of the vertices the internal portion of the energy function is dependent on the angle between the edges at the respective vertex and in that the external portion of the energy function is determined by the variation of the image parameter values in a single direction that bisects the angle between the edges at the respective vertex. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19)
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9. Arrangement for determining a contour in a space of image parameter values, the arrangement comprising
a memory for storing image parameter values in said space in the form of a matrix of pixel values; -
a display for displaying a two-dimensional image determined from said pixel values; a pointing device for indicating initial vertex positions in the displayed image for defining a seed contour; a computer, having access to said memory and said vertex positions, for evaluating an energy function comprising an internal portion which is a function of a curvature at each of the vertices and an external portion determined by a variation of image parameter values at the location of each of said vertices; the computer being arranged for determining a final contour by continuously varying the position of the vertices till the energy function reaches a minimum, while for each of the vertices the internal portion of the energy function is dependent on the angle between the edges at the respective vertex and in that the external portion of the energy function is determined by the variation of image parameter values in a single direction that bisects the angle between the edges at the respective vertex. - View Dependent Claims (20)
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Specification