VIDEO WEB INSPECTION SYSTEM EMPLOYING FILTERING AND THRESHOLDING TO DETERMINE SURFACE ANOMALIES

Method and apparatus for inspecting the surface of a moving web of homogeneous material for anomalies, the apparatus including a light source for illuminating the web surface and a light sensitive detector for receiving data from the web surface. The data is representative of the light reflected from the surface, as the light is affected by surface anomalies and background information. Computational means are provided for receiving output data from the detector in response to the data the detector receives from the web surface, and for processing the output data in a manner that determines the presence of surface anomalies. The computation means includes a plurality of filters for transforming the surface data in a manner that effects substantial elimination of the background information, and means for establishing threshold levels for background information. In addition, automatic means is provided for modifying the threshold levels in response to changes in the reflectance, frequency, or contrast of background information received by the detector and forwarded to the computation means.