Color Digitizing and Modeling of Free-form 3D Objects

This paper deals with the problem of capturing the color information of physical 3D objects thanks to a class of digitizers providing color and range data, like range finders based on structured lighting. It appears typically in a modeling procedure that aims at building a realistic virtual 3D model. The color data delivered by such scanners basically express the reflected color intensity of the object and not its intrinsic color. A consequence is therefore the existence, on the reconstructed model, of strong color discontinuities, which result from acquisitions done under different illumination conditions. The paper considers three approaches in order to remove these discontinuities and obtain the desired intrinsic color data. The first one converts the reflected color intensity into the intrinsic color by computation, using a reflectance model and known acquisition parameters. The use of simple reflectance models is considered: Lambert and Phong, respectively for perfectly diffuse and mixed diffuse and specular reflection. The second approach is a hardware solution. It aims at using a nearly constant, diffuse and omnidirectional illumination over the visible parts of the object. A third method combines the first computational approach with the use of several known illumination sources. An experimental comparison of these three approaches is finally presented.