Since diffuse reflections are direction insensitive, the paper is segmented from the drum by finding regions which exhibit less change in intensity when the lighting direction is changed. Each stack of drums will contain a single drum size. Each drum has a homogeneous paint color. However, there is no restrictions on or requirement for apriori knowledge of the specific color. Projected laser dots are easily discernible on flat-painted surface.
Specular reflections are easily discernible on glossy-painted surfaces.
The height of the camera with respect to the floor is known. An image will contain the horizontal center and either the top or bottom edge of a drum. Each of these steps is described below. The process of finding the center of the drum starts by imaging the laser dots projected onto the surface of the drum. For each combination of 3 dots, the virtual vertical cylinder on which the dots lie is found.