Lighting for automated visual inspection: theory and practice for transparent and glossy objects

Finn Johannessen

doi:10.1117/12.196086

23 November 1994 Lighting for automated visual inspection: theory and practice for transparent and glossy objects

Finn Johannessen

Proceedings Volume 2249, Automated 3D and 2D Vision; (1994) https://doi.org/10.1117/12.196086
Event: Optics for Productivity in Manufacturing, 1994, Frankfurt, Germany

Abstract

The overall performance of computer vision systems for automated visual inspection depends to a large extent on the quality of the lighting. This is especially the case when objects containing transparent and glossy parts have to be inspected, due to their special optical properties, which give rise to particular problems as well as possibilities. A typical aspect of this type of objects is, that the resulting image has a high dependency on the directional properties of the illumination, i.e. from where the light comes. This paper describes how a systematic search for the optimum lighting can be undertaken by making a classification and survey of the possible types of lighting that can be made with elementary shapes of light sources. For a series of different types of lighting created with these sources the resulting images for a typical object, chiefly transparent, are shown. In addition to the directional properties, some effects of polarization is treated. The images exhibit great differences both in general appearance and in ability to reflect the features to be inspected, whether these are shape, defects or contaminants. This shows, that there is a great variation in the possible ways to illuminate objects of this type, and it stresses the importance of optimizing the lighting to the particular task. Finally a case story with an object made from different materials, opaque and transparent, is treated. As is often experienced in practice, the best illumination results as a compromise between some more or less contradictory demands.

Citation Download Citation

Finn Johannessen "Lighting for automated visual inspection: theory and practice for transparent and glossy objects", Proc. SPIE 2249, Automated 3D and 2D Vision, (23 November 1994); https://doi.org/10.1117/12.196086

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