On estimation of perceived mottling prior to printing

Print mottle is one of the most significant defects in modern offset printing influencing overall print quality. Mottling can be defined as undesired unevenness in perceived print density. Previous research in the field considered designing and improving perception models for evaluating print mottle. Mottle has traditionally been evaluated by estimating the reflectance variation in the print. In our work, we present an approach of estimating mottling effect prior to printing. Our experiments included imaging non printed media under various lighting conditions, printing the samples with sheet fed offset printing and imaging afterwards. For the preprint examinations we used a set of preprint images and for the outcome testing we used high resolution scans. For the set of papers used in experiment only uncoated mechanical speciality paper showed a good chance of print mottle prediction. Other tested paper types had a low correlation between non-printed and printed images. The achieved results allow predicting the amount of mottling on the final print using preprint area images for a certain paper type. Current experiment settings suited well for uncoated paper, but for the coated samples other settings need to be tested. The results show that the estimation can be made on the coarse scale and for better results extra parameters will be required, i.e., paper type, coating, printing process in question.