Quantified and perceived unevenness of solid printed areas

Abstract

Mottling is one of the most severe printing defects in modern offset printing using coated papers. It can be defined as undesired unevenness in perceived print density. In our studies, we have implemented two methods known from the literature to quantify print mottle: the standard method for prints from office equipment and the bandpass method specially designed for mottling. Our goal was to study the performance of the methods when compared to human perception. For comparisons, we used a test set of 20 grey samples which were assessed by professional and non-professional people, and the artificial methods. The results show that the bandpass method can be used to quantify mottling of grey samples with a reasonable accuracy. However, we propose a modification to the bandpass method. The enhanced bandpass method utilizes a contrast sensitivity function for the human visual system directly in the frequency domain and the function parameters are optimized based on the human assessment. This results a significant improvement in the correlation to human assessment when compared to the original bandpass method. © Springer-Verlag Berlin Heidelberg 2005.