Perceived Image Quality of Printed Images and Their Relation to Paper Properties

In printing the final color image reproduction quality depends on the quality of the digital image as well as the properties of the printing system and the paper used. Although it is well known that the paper has a large influence on the print result it is seldom specified according to image quality attributes. Computer screens, digital cameras and printers are all technically specified with respect to resolution (number of pixels and dots per inch), gradation (bit depths) and primary color channels. The technical specification of paper on the other hand mainly includes properties of the unprinted paper that provide limited information about the appearance of the printed image. However, the characterization of paper is not as straight forward as the performance is not only related to the paper properties but also to a high extent to its interaction with the printing system. One way to indicate the color reproduction quality of images is to determine the modular transfer function (MTF). Several studies have derived the MTF of paper for certain printing situations (Bouzit 2002, Koopipat 2000 and Rogers 2000) and stated the influenced of not only the physical properties of the paper but also by the interaction between paper and ink. The most decisive properties found on paper MTF are ink penetration, ink spreading and the optical properties of the paper. Moreover, these paper properties can be associated to color rendering attribute associated with image quality such as color gradation, color gamut volume and image sharpness. In this study, these three attributes have been varied prior to printing in two sets of test images representing office paper and photo inkjet paper respectively. Color gamut volume, color gradation and sharpness were varied simultaneously according to a statistical experimental design thus producing a subset of modified versions for each image in the test set. Furthermore, a visual assessment study was carried out in order to study the effect of the modifications on the perceived impression of the printed images. Finally, the data from the visual assessment study was analyzed in order to reveal how the different attributes influenced the perceived color rendition. The results from the study showed that small changes in the varied attributes produces large response on the perceived color rendering quality and that the most important parameter is color gamut volume.