 The Lambertian reflectance model is widely used for
modeling illumination variations and is a good approximation for diffuse object surfaces.The DLN is a hybrid undirected-directed generative model that combines DBNs with the Lambertian reflectance model.In the DLN, the visible layer consists of image pixel intensities v ∈ RNv, where Nv is the number of pixels in the image.