a test patch generator for electrophotographic machines automatically adjusts test patch exposure to predetermined values regardless of operator - initiated changes in exposure settings . a main illumination source exposes an original document . integrating the main illumination source produces an electrical signal representative of the amount of such exposure . the signal is modified by a factor selected in accordance with the exposure setting , and the modified signal is used to produce a latent image test patch on a photoconductor member , the patch having an exposure value corresponding to the modified signal . once the patch is toned , a sensor can be used to measure the patch density and any necessary adjustments to the process parameters made .