Dynamic range in automated visual web inspection

We analyze the factors affecting the dynamic range of an automated visual web inspection system and characterize the dependence of the image quality on the performance of the imaging unit. The objective is to form a basis for the systematic design and evaluation of imaging in web inspection. The major noise sources are reviewed and a simple method for the determination of the noise generated in the imaging unit of a web inspection system is proposed. In addition to this, the effects of the nonlinearity in the system response and of the optical characteristics to the attainable dynamic range are discussed. In the paper several measured characteristics of exemplary web inspection imaging units are presented. The results of these measurements sketch the order of the effect of various factors on the dynamic range in actual inspection applications. Finally, an analysis of the dynamic range in a paper inspection application is presented in order to illustrate the relationship between the properties of the imaging unit and the performance of the inspection system. (C) 1998 Society of Photo-Optical Instrumentation Engineers. [S0091-3286(98)04501-2].