A process classifies objects in a scene. The process receives a captured IR image of a scene taken by a 2-dimensional image sensor array of a camera system while one or more IR illuminators of the camera system are emitting IR light, thereby forming an IR intensity map of the scene with a respective intensity value determined for each pixel of the IR image. The process uses the IR intensity map to identify a plurality of pixels whose corresponding intensity values are within a predefined intensity range, and clusters the identified plurality of pixels into one or more regions that are substantially contiguous. The process determines that a first region of the one or more regions corresponds to a specific material based, at least in part, on the intensity values of the pixels in the first region. The process then stores information in the memory that identifies the first region.