Preliminary analysis of image processing-based evaluation of embossing quality

Abstract

The embossing process in graphic industry utilizes custom made dies to create raised or lowered permanent relief patterns according to the design. It can be combined with other print finishing embellishments, such as foil stamping or pearlescent coating, but the simplest version of this process, the blind embossing is also a very effective technique to create a distinguished and sophisticated look. The quality control of embossing features was done only visually for a long time, but in the recent years it became an important target for graphic instrument manufacturers focusing on the embossing depth, as one of the most important parameters for high quality processing. This analysis was aiming to investigate the applicability of a simple flatbed scanner and the developed image processing algorithm for embossing quality evaluation. The results of detailed visual assessment of all scanned paper samples and the obtained values of average greyscale difference (shadow-based contrast), showed that single-level embossed samples can be realistically digitalized using a simple flatbed scanner, as an image acquisition equipment. Additionally, the proposed image feature, the shadow-based contrast had increasing tendency by increasing the applied compression force, in general, suggesting that it has a potential as an objective measure for the deformation rate in the embossing quality evaluation. The obtained results gathered for different combinations of observed parameters (paper grade, basis weight, type of test elements on the embossing dies) with the optimal compression forces, implied that the shadow-based contrast could be used as a reference parameter to ensure adequate visibility of embossed elements by defining the minimum value of needed contrast.