An MTF Analysis of Papers

摘要

Resolution and tone reproduction characteristics of all hardcopy images on paper are significantly influenced by the way light scatters in the paper. However, little has been published on experimental techniques for measuring light scattering and resolution characteristics of paper. Three experimental techniques are discussed in the current work. The first is a direct measure of paper MTF by microdensitometric scans of illuminated edges projected onto the paper. This technique is tedious and of intrinsically low precision. The second technique is based on Kubelka-Munk theory and derives MTF behavior from the Kubelka-Munk equations and experimental measurements of paper reflectance. This technique has the advantage of relating paper MTF to the fundamental metrics of light scattering and light absorption. However, the accuracy of the technique is questionable due to the assumptions intrinsic to Kubelka-Munk theory. The third technique involves modeling the Yule-Nielsen effect of optical dot gain and fitting the model to experimental data. The data are generated by image analysis of idealized halftone patterns formed by placing high-resolution halftone line screens in close mechanical contact with the paper under analysis. This technique is shown to provide estimates of paper MTF with significantly higher precision than traditional microdensitometry scans of illuminated edges. Experimental data are collected for a wide variety of hardcopy substrates, and the results are used to examine some of the assumptions inherent in applying Kubelka-Munk theory to papers.