Fig. 1. Scheme of the sorting machine.
3.2. Inspecting unit and computer vision system
The prototype used two progressive scan cameras to acquire 512 384 pixel RGB (Red, Green and Blue) images with a
resolution of 0.70 mm/pixel. Both cameras were connected to a 28 J. Blasco et al. / Journal of Food Engineering 90 (2009) 27–34 computer, the so-called ‘‘vision computer” (Pentium 4 at 3.0 GHz), by means of a single frame grabber that digitised the images and stored them in the computer’s memory. The illumination system consisted of two 40 w daylight compact fluorescent tubes located on both sides of each conveyor belt, thus making a total of 14 tubes. Tubes were used together with high frequency electronic ballast to avoid the flicker effect. This illumination was powerful enough and did not produce shadows. The influence of bright spots in the scene caused by direct lighting on wet surfaces, which could
alter the perception of the colour by the inspection system, was minimised by using cross-polarised filters placed above the lamps and on the camera lenses. The scene captured by each camera had a length of approximately 360 mm along the direction of the movement of the objects and a width that allowed the system to inspect three conveyor belts at the same time. The entire system was housed in a stainless steel chamber. A picture of the whole prototype is shown in Fig. 2.