Teun Baar

Printing gloss effects in a 2.5D system

An important aspect for print quality assessment is the perceived gloss level across the printout. There exists a strong relationship between the surface roughness of a printout and the amount of specular reflection which is perceived as gloss variations. Different print parameters influence the surface roughness of the printouts such as the paper substrate, the type of inks and the print method. The lack of control over the print’s surface roughness may result in artefacts such as bronzing and differential gloss. Employing a 2.5D or relief printing system, we are able to control the printout roughness by manipulating the way the ink is deposited in a layer-by-layer basis. By changing the deposition time in between two layers of white ink and the order on which the pixels are printed, we achieve different gloss levels from a matte to a glossy appearance that can be controlled locally. Understanding the relationship between different printing parameters and the resulting gloss level allows us: to solve differential gloss artefacts (to obtain a print with a full gloss or matte finish) and to use the local gloss variations to create reflection effects in the printouts. Applications related to security printing have also been explored. Our results showed a reduced level of gloss toward a matte appearance as the ink deposition time between the layers was increased, allowing more time for the ink to dry between passes. We measured the gloss levels using a gloss meter and a psychophysical experiment was conducted to validate our measurements and observations.

Reproducing oil paint gloss in print for the purpose of creating reproductions of Old Masters

In the field of Fine Art reproduction, 3D scanning plus 3D printing, combined with dedicated software, now allows to capture and reproduce the color and texture of oil paintings. However, for life-like reproduction of the material appearance of such paintings, the typical gloss and translucency must also be included, which is currently not the case. The aim of this paper is to elaborate on the challenges and results of capturing and reproducing oil paint gloss (next to texture and color) using a scanning and printing system. A sample was hand-made using oil paint and acrylic varnish, and its gloss was then reproduced. A gloss map of the painted sample was acquired using a high end DLSR camera and a simple acquisition protocol. Next, Océ High Resolution 3D printing technology was used to create samples with spatially varying gloss. For this, two different strategies were combined: (1) multilevel half-toning of the colors was used to reproduce matte color layers, and (2) varnish was half-toned on top in increasing coverage to recreate increasing gloss levels. This paper presents an overview of the state-of-the-art literature in gloss reproduction and perception, our process of reproduction as well as the visual evaluation of the quality of the created reproduction.

A survey of 3D image quality metrics for relief print evaluation

This paper aims to give a survey of research related to the assessment of image quality metrics of 2.5D and 3D prints. Future research will focus on the ability of combining relief and glossiness in printouts created by a prototype printer that uses multiple layers of ink and varnish. Reproducing these relief or 2.5D surfaces brings out the challenge of evaluating the quality of the outcome. Although, for some decades, active research has been done on 2D image quality assessment, quality evaluation of images in a higher dimension is yet in an early stage. Currently, there are no image quality metrics defined for relief prints and much about their perception is still unknown. As a first step to come up with such metrics, the following survey explores research on the quality assessment of 3D prints, objects, computer simulations and television to relate to future image quality metrics for relief prints.

Towards gloss control in fine art reproduction

The studies regarding fine art reproduction mainly focus on the accuracy of colour and the recreation of surface texture properties. Since reflection properties other than colour are neglected, important details of the artwork are lost. For instance, gloss properties, often characteristic to painters and particular movements in the history of art, are not well reproduced. The inadequate reproduction of the different gloss levels of a piece of fine art leads to a specular reflection mismatch in printed copies with respect to the original works that affects the perceptual quality of the printout. We used different print parameters of a 3D high resolution printing setup to control the gloss level on a printout locally. Our method can be used to control gloss automatically and in crucial applications such as fine art reproduction.

Image ghosting reduction in lenticular relief prints

Commonly known lenticular prints use a lens-like system superimposed on a standard 2D print to control the light sent into each direction. Thanks to our 2.5D or relief printing system, we are capable of creating a lenticular effect embedded directly on the prints that does not require the use of a system of lenses. On a zigzag-shaped surface composed of continuous small triangles two source images are interlaced and printed on the sides of the triangular structures, each side corresponding to one of the two intended views. The effect of crosstalk or ghosting is often encountered in lenticular prints. Ghosting occurs when some parts of one source image remain visible for the illumination or viewing direction corresponding to the other source image. In this work, we use an image-content-driven technique that identifies the regions in the source images that are prone to cause ghosting for a given set of viewing angles. For the purpose of eliminating this artefact, a model of the ghosting effect appearance is implemented and used for compensation. We have observed improvements in the quality of the lenticular effect, however the impact on the quality of the prints still needs to be evaluated.