A new effect during light propagation simulation in the Fresnel region is discovered. Image multiplying and high-frequency noise effects are caused by the sampling of the complex light field. Image multiplying is observed in the case of the standard integral calculation. High-frequency noise is observed in the convolution approach. These effects are observed in a computer simulation only and do not exist in nature. The analysis of these effects enable us to define the range of the numerical algorithms application. © 2003 Society of Photo-Optical Instrumentation Engineers.