Multisource and color lighting for detection of small protuberance

In typical machine vision problems such as quality control or object location, it is often the case that elements of interest are small protuberances over a surface. We present an innovative and robust approach aiming at detecting such protuberances. Its basic ideas are: a) to detect the shadows produced by the protuberances, b) to use several light sources simultaneously to enhance detection. Each light source produces a different set of shadows; combining the shadows produced by all light sources allows to locate the protuberance, since these shadows are the only significantly varying patterns between views. Rather than using several white light sources in sequence, it is possible to use simultaneous color sources with appropriate filters to separate the image into independent channels. The approach has been validated on a concrete problem with highly variable protuberances and non-planar surfaces. The results confirm the robustness of this approach, that could be used for other problems as well.