Differential Spectra - A New Method for Print Quality Analysis from Pictures, 1996 International Printing & Graphic Arts Conference Proceedings

B. Foyn, O. Levhaugen, O. Solheim

The Norwegian Pulp and Paper Research Institute

This paper presents a novel technique of measuring print quality where the analysis can be carried out from pictures. It is based on information theory and visual perception, and incorporates the fact that the human eye is not equally sensitive to all frequencies in graylevel change in print. Using cross correlation, identical parts of a reference image, typically, the original, and an image of a printed picture are picked out. Calculating the difference between the power spectra of the two images, the degradation of the reference picture can be measured. The differential spectrum may be multiplied with the human contrast transfer function (CTF) to improve the visual significance of the results. Results show a good correlation to visually evaluated print quality preferences, and show that it is possible to measure the visual appearance of print quality from pictures.