ABSTRACT
In any visual inspection problem the quality of the lighting is paramount: Too often key features are obscured by glare, or the intensity of light reaching the detector is insufficient. This chapter discusses the purposes of lighting and provides background for the detection of black skin and blood spots in cod fish fillets. There are four main problems using front lighting in the detection of blood spots and ventral skin. These are: glinting, shadows, unsharp edges between the different features and the flesh, and unsharp edges between the flesh and the transport belt. Depending on the nature of the features to be inspected, the designer must first choose one of the following techniques in order to solve the spatial distribution problem. These are: front lighting, back lighting, and structured lighting. When designing the optical subsystem, one must try to reduce the demands on the image processor to a trivial level by giving to it the best possible images to analyze.
