A basic PMS system uses lighting from four or more directions to cast a directional shadow around raised or sunken features on an object. The illumination may be a ring light with four 90 degree quadrants, an array of four bar lights, or any other arrangement that produces directional lighting. The feature map can be applied through different algorithms to show surface details that are hard to find or can't be detected in pure visual or machine vision images.
Tire inspection with PMS
The images in this example were captured with four long bar lights arranged in a square pattern around the tire.
The quadrants were fired in sequence to create the East, South, North, West images on the left.