The high image quality of recent xerographic and direct marking products are achieved in part by accurately placing marks on the paper to microns precision at substrate speeds of up to 500 mm/sec. Accurate measurement techniques are required to develop products with this capability. Measurements of the positions of marks on paper to sub-micron precision can be achieved by printing and scanning specific test patterns. Even though scanner resolutions are tens of microns, the measurement precision is increased orders of magnitude by using various signal processing techniques and massive statistical averaging on the hundreds of megabytes of information. Examples include (1) measurement and adjustment of an LED bar imager to achieve uniform images, (2) measurement of beam positions and intensities due to imperfections in motor polygon assemblies and multiple beam images, and (3) signal processing techniques to compensate for imperfections in contact image sensors.