Method and apparatus for constraint-based texture generation

Abstract

A method and apparatus for texture mapping a surface. The method is applicable to texture mapping either a two-dimensional representation (image) of a three-dimensional surface as well as a three-dimensional computer model of a three-dimensional surface, such as a triangular wire mesh model. In one embodiment, the texture mapping process involves user-specification of a plurality of constraints, including texture flow constraints, texture discontinuities, and surface underfolds. A triangular wire mesh model of the surface to be textured is generated. The mesh allows a continuous texture distribution to be specified as a linear interpolation of texture values at the triangular vertices. User-specified constraints are preserved as edges within the triangular mesh. The triangular mesh is used to compute a weighted energy functional expressed in terms of nodal texture values. The global value of this functional serves as a measure of how closely the user-specified and physics-based constraints are met by a particular texture distribution. The optimal texture distribution is found by determining the set of nodal values which minimizes this functional, through an iterative process that is recursively applied to each nodal value using the results of a previous iteration. In accordance with one aspect of the invention, the results of previous optimizations may be used as the starting point for subsequent refinements of the texture distribution, in the event that greater levels of photorealisim are necessary. During this recursive procedure the triangular mesh is progressively refined using an adaptive subdivision procedure which allows local texture variations to be more accurately expressed whilst optimizing the overall mesh density against calculational efficiency.

1 . A method for creating a texture map for a three-dimensional surface, comprising
 (a) defining a triangular mesh model of said surface;   (b) providing at least one user-specified texture constraint;   (c) computing a weighted energy functional for said triangular mesh, said weighted energy functional comprising a plurality of nodal texture values computed in accordance with said at least one user-specified texture constraint;   (d) iteratively recomputing said nodal texture values to converge said weighted energy functional toward a minimum value.   
   
   
       2 . A method in accordance with  claim 1 , wherein said at least one user-specified texture constraint comprises a texture flow constraint. 
   
   
       3 . A method in accordance with  claim 2 , wherein said at least one user-specified texture constraint further comprises a texture discontinuity. 
   
   
       4 . A method in accordance with  claim 3 , wherein said at least one user-specified texture constraint further comprises a texture underfold constraint. 
   
   
       5 . A method in accordance with  claim 4 , wherein said at least one user-specified texture constraint further comprises a texture height profile constraint. 
   
   
       6 . A method in accordance with  claim 1 , wherein said step (b) of providing at least one user-specified texture constraint comprises the steps of:
 (b)(1) displaying a two-dimensional image of said surface on a computer display;   (b)(2) using a user-input device to superimpose a free-form line on said image.   
   
   
       7 . A method in accordance with  claim 6 , wherein said free-form line approximates the flow of said texture on said surface. 
   
   
       8 . A method in accordance with  claim 6 , wherein said free-form line corresponds to the location of a discontinuity in said texture. 
   
   
       9 . A method in accordance with  claim 6 , wherein said free-form line corresponds to the location of an underfold in said surface. 
   
   
       10 . A method in accordance with  claim 6 , wherein said free-form line corresponds to the location of a height profile in said surface. 
   
   
       11 . A method in accordance with  claim 1 , wherein said energy functional approximates the total strain energy for said triangular mesh.