A color processing for displaying reality-based three-dimensional digital models in RTR

The color survey of plastered painted façades and monumental-historical buildings represents a difficult operation due to a lot of factors such as subjective aspects of visual perception, objective characteristics relating to sources of lighting and the way one watches something. The color survey, usually, refers to three methods: - transcript of a sample; - visual comparison; - instrumental survey. These methods, besides to present problems beyond the ability of an actual sample of existing matter, they aren’t able to ensure the correct perception of color on an RGB monitor or its faithful reproduction on a print support. No one of these methods, in fact, is able to assure a right color checking on a wide surface, and with a non-uniform color. The problem is much more sensitive when the goal is to create reality-based 3D digital models, where is more useful to identify color, texture, and reflectance properties of surfaces, trying to ensure fidelity of the perceived color, than to guarantee the color measured. The use of digital processes for the reproduction of the real color let us to identify color and diffuse reflectance extended to the whole surface artifact, just using few shots and color temperature controlled by software, in order to obtain an high accuracy color reproduction of the sample area. When we need to map 3D models with real-based images the main topic, in the acquisition phase, is to research the relationship between incident light and reflected one, in a specific point above the surface, a problem that, in its general formulation, requires knowledge and control of light sources and the environment influence to the measurements. From an operational point of view these phases are known as color processing, a set of steps that include: - color acquisition; - texture mapping pre-processing by setting off ambient light and eliminating shadows and specular reflections; - texture re-alignment on the geometric model; - texture size reduction and definition of the Level of Detail. The paper reports processes and methodologies developed in order to achieve photo-realistic 3D models using digital images projected onto the geometry of 3D digital models. It describes, therefore, the measurements procedures adopted for images acquisition, color management and color information mapping procedure on the 3D model.