A nonlinear model for holographic recording materials is used to evalu
ate the signal-to-noise ratio in diffuse-object holograms. A compariso
n of this model with the linear model proposed by Upatnieks and Leonar
d [J. Opt. Sec. Am. 60, 297 (1970)] shows that our model justifies the
experimental results obtained for dieletric holograms at high density
before bleaching.