Gloss is an image or substrate attribute that describes how much specular reflection is observed from a surface of a substrate. Specular reflection is the mirror-like reflection of light from a surface, in which light from a single incoming direction is reflected in a single outgoing direction. Because the surface of the substrate is not always perfectly flat, the light reflected from the surface of the substrate is not similar to what would generally be reflected from a mirror. When a surface of a substrate is rough, the percentage of the light that is reflected as specular reflection is less. In general, the rougher the surface, the lesser the chance of the reflected light is going to travel in the direction of the specular reflection. By varying the roughness of the surface, different types of finishes may be achieved.
A related art gloss technology is used to generate image-wise gloss effect by printing using particular paper, ink, halftones, and manner of fusing the ink onto the paper. By adjusting these parameters, a gloss of the printed image can be modulated, creating a subtle image that may be viewed when the paper is held a certain way. The technology is referred to as glossmark, and is described in US Patent Publication No. 2004/0001233 titled “Protecting Printed items Intended For Public Exchange with Glossmarks” and US Patent Publication No. US2004/0156078 titled “Application of Glossmarks for Graphics Enhancement”. Glossmark technology is limited insofar as it can only be used to print images having a limited amount of colors with small contrast.
Another related art technology that may affect a roughness of a surface is laser engraving. Other related art image surface modification methods include laser engraving, which includes marking an object by removing material from a solid surface using a high power laser. Laser engraving requires high energy: power density and energy density. Because of the high energy required, the speed of laser engraving is slow. Further, laser engraving generates fumes and dust, which are neither environmentally nor user friendly. Finally, image resolution of laser engraving is limited.