Abstract: Wavelet radiosity is, by its nature, restricted to parallelograms or triangles. This paper presents an innovative technique enabling wavelet radiosity computations on planar surfaces of arbitrary shape, including concave contours or contours with holes. This technique replaces the need for triangulating such complicated shapes, greatly reducing the complexity of the wavelet radiosity algorithm and the computation time. It also gives a better approximation of the radiosity function, resulting in better visual results. Our technique works by separating the radiosity function from the surface geometry, extending the radiosity function defined on the original shape onto a simpler domain -- a parallelogram -- better behaved for hierarchical refinement and wavelet computations.