This is not a painting: Scanning and printing a painting's appearance

The appearance of a painting cannot solely be described by the depiction that it presents to the viewer. When viewing the artifact in real life, we find that the painted surface is in effect a three-dimensional landscape of paint. Paintings, “moveable, largely two-dimensional images created for the primary purpose of providing a visual experience”,1 can be created using a vast variety of materials on a range of supports. They are commonly built up as a complex stratigraphy of layers, generally consisting of a support, ground layer(s), one or multiple layers of (semi-) transparent paints, and in many cases a protective varnish layer. The current appearance of a painting is determined by the way a painter used and applied the materials, but also effects of aging, conservation and restoration treatments, which all continue to influence the physical state of a painting. Historically, cultural heritage (CH) reproductions were hand-crafted, and created for instance to disseminate or replace artworks, or to train in the skill of their creation. Also modern reproductions — or facsimiles — are still large hand-crafted, and for instance serve to provide access to (fragile) artworks or even complete (CH) sites, or to recreate their original appearance. Alternatively, reconstructions might reside only in the virtual domain. The continued development of digital imaging and digital fabrication technology (i.e. 3D printing) provides new opportunities for appearance reproduction, also suitable for application in the CH domain. If we want to replicate material appearance, we need to understand how (the appearance of) material is perceived. A material is, however, not observed directly, but has to be lighted, and via the light that is scattered by the material humans can perceive it. Appearance is therefore the light-material-confounded proximal stimulus for the human visual system (HVS). Even though we see, recognize and interact with a vast number of materials every day, and can effortlessly distinguish between them, it turns out that the perceptual mechanisms that underlie this, are still quite poorly understood, including linking individual appearance attributes to measurable and fabrication parameters. One of the consequences of this is that an integrated approach to (total) appearance reproduction, including color, topography/ texture/shape, gloss and transparency/translucency, is still lacking.