Projective analysis of 2-D images

The use of the heatlike equation has been extended to the projective case in order to find a projective analysis of curves and images; unfortunately, this formulation leads to a fifth-order partial differential equation (PDE) that is not easy to implement. Thanks to the use of a three-dimensional (3-D) homogeneous representation of a picture, we present an alternative. Roughly speaking, it is a kind of decomposition of the heatlike formulation with well-posed second-order PDEs. The number of parameters goes from one to three (the scale parameter and two direction parameters). Moreover, this study allows us to propose a simplified multiscale analysis, which is given by an unique PDE (one parameter), for the subgroup of the projective transformations associated, up to a nonzero scalar factor, to an orthogonal 3/spl times/3 matrix.