Lighting Design for Industrial Machine Vision

Abstract

The purpose of the lighting in an industrial machine vision application is to produce an image that is well matched to the camera and vision system. The brightest areas of the scene should cause a sensor illuminance that is just below the camera's saturation level and the video signal from the darkest significant areas of the scene should lie just above the vision system's noise level. This paper describes the fundamental principles and the techniques used to design lighting that meets these requirements. The camera's transfer function, the vision system's noise level, and the relative lens aperture are used to calculate optimal luminances for the brightest and darkest areas in the scene. The necessary reflectivity coefficients for the objects in the scene are measured and lighting is designed which produces the correct object luminances in both the specular highlights and the diffuse background areas of the scene. We show how to specify the light sources required to produce the lighting and present an example of printed circuit board inspection. The burden that this design method places on the vision algorithms is also discussed.