Specular-Reduced Imaging for Inspection of Machined Surfaces

Specular surfaces pose difficulties for machine vision. In some applications, this may be further complicated by the presence of marks from a machining process. We propose a system that directly illuminates machined specular surfaces with a programmable array of high-power light-emitting diodes. A novel approach is described in which the angle of the incident light is varied over a series of images from which a specular-reduced median image is computed. A quality factor is used to quantitatively characterize the degree to which these specular-reduced median images approximate a diffusely lit image, and this quality factor is shown to depend linearly on the number of specular images used to produce the single specular-reduced median image. Defects such as porosity and scratches are shown to be identifiable in the specular-reduced median images of machined surfaces.