An electrophotographic color proof generating apparatus includes a charger station, an exposure station, a toning station, and a dryer station. A system electronically controls and monitors the quality of the proofs being generated by the electrophotographic process. The process parameters of electrostatic voltage and transmission density are sensed from test patches, sometimes referred to as control patches. The parameters are monitored by the control electronics used to regulate imaging subassemblies and to track film and toner characteristics to provide optimum image density on the photoconductor. It is the purpose of the process control algorithm that resides in the control electronics to control the proofing process to achieve the desired aim transmission density on the photoconductor. The slope of the Density/Delta-V curve and the density (DMAXNET) are used to predict the working delta-V aim which governs toning control. Any deviation from that density causes the control electronics to adjust the charger grid voltage and the toner electrode bias to bring the test patch back to the required aim density. The voltage read by a first electrometer is an indication of charging efficiency and when compared to the voltage read by a second electrometer, the voltage decay rate may be determined. These electronic voltage readings are used to determine film characteristics of speed and minimum exposure voltage.