Evaluation of perceptual resolution of printed matter (Fogra L-Score evaluation)

摘要

A new method has been developed to address the objective evaluation of perceived resolution of printed matter. To achieve this, a psychophysical experiment has been designed and conducted that ranked typical test prints representing the manifold of printing processes and substrates. A scanner based method has been developed that computes a score value between 0 and 100 termed Fogra L-Score. It is based on the idea to identify a predefined signal in an image (print). The predefined signal is a perfect representation of the "perceived resolution domain" by means of a test target (RIT ConRes-target) that covers systematic variations of the two governing parameters of perceived resolution namely contrast and spatial resolution. The printed images to be evaluated have been scanned and pre-processed. The level of closeness between the reference (digital representation) and the printed matter (scanned print) have been determined by a 2-dimensional normalized cross-correlation (on the CIEL*-channel). The resulting correlation coefficients have been compared against findings of the performed psychophysical experiment. Finally a framework will be presented that also allows for spatial filtering to address different intended viewing distances as well as chromatic test charts.