1. A method for rendering an inhomogeneous scattering medium represented by a density field comprising an approximate model density field and a residual density field, the method comprising: computing an approximate source radiance based on the approximate model density field; computing an effective exitant radiance by compositing the approximate source radiance by integrating the approximate source radiance along a view ray in both the approximate model density field and the residual density field; and rendering an image of the inhomogeneous scattering medium based on the effective exitant radiance.