1. A method of detecting banding defects in the output of an image output device comprising the steps of: generating a test pattern at a known time; analyzing the test pattern to generate spectral banding defect records; storing the spectral banding defect records in memory linked to a time stamp indicating known time when the test pattern was generated; repeating the generating, analyzing and storing steps at a plurality of different known times to generate a database of time stamped spectral banding defect records; reconstructing an isolated spectrum from each spectral banding defect record in the database; constructing a cumulative spectrum by probabilistic summation of isolated spectra; analyzing the cumulative spectrum using an image quality assessment/analysis engine.