Printed image appearance changes when lit
US researchers have developed a special paper that can be used with existing printers to create images of scenes whose reflectance properties are preserved.
The appearance of an object changes when it is lit from different directions, providing a perceptual cue to its shape and the material from which it is made. Unfortunately, when printed on paper, the effect is lost. A photographic print represents just one appearance of a scene, regardless of the ambient lighting used when the print is viewed.
The appearance of objects in a scene depends upon the incident illumination, the surface Bi-directional Reflectance Distribution Function (BRDF) -- a function that defines how light is reflected from the surface of the objects -- and the orientation of the surface of the objects themselves. But typical printers cannot print images which react to incident illumination because they use inks with a limited range of BRDFs and print on paper which is flat.
Now, however, researchers at the multimedia communications and networking lab within Hewlett-Packard Laboratories (Palo, Alto, CA, USA), at the University of California Santa Cruz (Santa Cruz, CA, USA) and at 3M (St. Paul, MN, USA), have developed a special paper that can be used with existing printers to create images of scenes whose reflectance properties are preserved.
The paper itself sports a hexagonal array of spherical depressions that have a specularly reflective surface. By selectively printing opaque or partially opaque ink on portions of that surface, the researchers have shown that the appearance of the images that are created can be controlled as a function of the direction in which the paper is lit.
At the present time, they have demonstrated that the technique can be used to create monochrome images, but they believe that the technique could be extended to produce color images as well.
The researchers recently described their work in detail in a paper “Printing Reflectance Functions” which was published in the May 2012 ACM Transactions on Graphics. The paper itself can be downloaded here.
-- Dave Wilson, Senior Editor, Vision Systems Design