Image Quality Metrics for Printers and Media

The most common computer peripheral used in office applications is the non-impact printer. The resolution, performance, and cost of these devices have improved dramatically during the 1990’s with output image quality emerging as a significant differentiator between competitive products. Just as printer manufacturers have become more aware of these developments, paper manufacturers have also begun to develop special purpose papers formulated to accept ink, wax or toner with little or no substrate-induced image degradation or distortion. These and other developments have created increased demand from imaging R&D and manufacturing quality engineers for precise tools to evaluate image quality in a non-subjective and repeatable manner. Just as importantly, these tools must be able to perform measurements in a timely manner in order to keep pace with ever shortening product development cycles. This paper will present a series of specific metrics that can be used for quantifying printed image quality for printer and paper manufacturers. Specifically we will present a methodology for evaluating color registration, resolution, text quality, dot quality, line quality and other image quality attributes. In addition we will discuss methods by which manufacturers have achieved fully automated image quality testing and the benefits achieved by automated testing in the areas of process monitoring and production quality. Typical Image Quality Tests Among the multitude of image quality tests available, there are a few that are particularly well suited to evaluate mediadependent image quality issues. These tests include: • Dot Quality (including tests for dot placement accuracy and variations in dot formation) • Halftone Quality (including tests for area coverage) • Line Quality (including tests for sharpness and edge noise as well as detectability tests for negative lines) • Text Quality (including tests for connectivity and edge degradation) • Color Quality (including tests for color registration and CIE L* a* b* measurements) • Smear/Overspray • Spatial Resolution 18 Figure 1a. Various levels of dot quality Figure 1b. Example of a dot quality test report