The development of global illumination and texture generation makes it possible to produce the most realistic images. However, it is still difficult or deficient so far to simulate bump texture effects while the interreflectiort of light being modeled by the present ray tracing or radioslty methods. A method of bump texture generation, being incorporated into the process of radiosity solution, is presented in the paper. The method is characterized by introduction of a perturbed radiosity map, established in the context of either progressive radiosity or standard radiosity solution. To calculate the perturbed radlosity, a concept of perturbed formfactors is proposed, and the algorithms for evaluating the perturbed form-factors are also given. As a result, a bilinearinterpolation shading scheme for perturbed surfaces is provided~ and the texturing method is easily added to a newly improved solution of progressive refinement radiosity for non-diffuse environment.