Abstract: The high dimensionality of the BRDF makes it difficult to use measured data for hardware rendering. Common solutions to overcome this problem include expressing a BRDF as a sum of basis functions or factorizing it into several functions of smaller dimensions which can be sampled into a texture.

In this paper we will focus on homomorphic factorization, which can be accelerated by preinverting the constraint matrix if the sampling pattern and the layout of the samples in the representation are fixed. Applying the preinverted constraint matrix is very fast and can be used to calculate factorization and material maps at interactive rates. We use this to derive shaders from painted examples. The technique presented in this paper allows interactive definition of materials, and, although based on physical parameters, this method can realize a variety of non-photorealistic effects.