1. A diagnostic system for diagnosing the cause of banding defects in a document processing system comprising: a scanner for generating image data by digitizing hardcopy samples obtained by printing or copying a test pattern on said document processing system an image quality analysis module adapted to receive said image data and to detect the presence of banding defects, said image quality analysis module further analyzing said image data relating to a detected banding defect to obtain quantified parameters of said banding defect and extracting key features from said quantified parameters; a diagnostic engine adapted to receive and analyze said key features, said diagnostic engine further identifying one or more malfunctions which are possible causes of said defect based on said analysis of said key features; a repair planning module adapted to receive the malfunctions identified by said diagnostic engine and select, from a plurality of service procedures, one or more of said procedures which are likely to correct said malfunction; a memory module for storing data and algorithms relating to said diagnostic system; a diagnostic control module adapted to control and coordinate the operation of said modules.