Colour Quality Assessment Of Inks On Papers Having Different Gloss Levels

The colour printing system consists of a printer, inks and the substrate, the gamut of which indicates whether its components are qualified. As ink-jet printers become more and more popular, how to enlarge the gamut of ink-jet printing medium draws more attention in the printing industry than ever. The improvement in ink production, novel techniques applied in printing colour management and the development of the multi-primary printer can all enlarge the gamut of the printing medium.As a common substrate, paper is the essential part of the printing system, which exerts unique influence in the gamut enlargement. The gloss of paper will affect the gamut of the colour image printed on it. Normally, paper substrate with higher gloss will show higher contrast and larger gamut, compared to common matte substrate.Currently limited quantitative researches have been done in printing industry on how the change of gloss will affect the gamut of the printed image. Hereby this study on how gloss of paper substrates influence the colour qualities of printed inks would combine the assessments of gloss and colour appearance, which shall surely promote the advancement of the colour printing technology and the development of related industrial products.Based on the various instrumental measurement and massive visual assessment data under different geometries, the relationships between the measurements of the gloss meter and other instruments and the results of visual assessments were analyzed in this dissertation for specular gloss and the cases with or without the gloss effect using the colour-difference formulae of CIELAB, CIEDE2000 and CAM02-UCS. Meanwhile, the impacts of gloss on colour appearance properties were also discussed by the employment of the colour appearance model of CIECAM02.With appropriate multi-gradient gloss references, the measurement of the gloss meter had considerably good correlation with the visual assessments on specular gloss; so it is qualified to be an alternative of time consuming visual experiments for the following discussion and analysis.By the application of related colour-difference formulae and colour appearance model, the 15/0 and 0/45 were considered to be good geometries for the inspection of colour properties with and without specular gloss component, respectively, compared to other geometries equipped in the current instruments, both of which had good correlations with the corresponding visual data.Among the three colour appearance parameters, gloss had the most obvious effect on colourfulness, and lightness came the second, while hue tended to be stable. Under the geometry of 0/45 representing normal visual condition, samples with higher gloss tended to have higher colourfulness and slight lower lightness; for both geometries with gloss effect of 60/60 used in visual experiemnts and 15/0 equiped in colour measurement devices, the decrement of colourfulness and the increment of lightness for the high gloss samples were remarkable with comparison to 0/45 as the normal visual geometry.Fast judgment of specular gloss based on digital camera would have good applications not only in the assessment of influence of gloss on colour, but also for the online quality control of glossy paper production. This study also carried out some exploration and research in this area, and the experimental results indicated that the established model performed well in predicting the specular gloss of the existing samples.Finally, on the basis of summarizing the research work of this dissertation, the perspectives of the future study were also forecasted.