2.3. Contour extraction
Fig. 2 illustrates the steps taken to extract the oyster contour for analysis. Fig. 2(a) shows the original image. As mentioned previously, it is captured with a near-infrared camera and a long-pass interference filter on a black conveyor belt. Image quality, especially image contrast, is enhanced with this setup. Otsu’s method is widely used to automatically select a binarization threshold based on the shape of the image histogram (Sezgin and Sankur, 2003; Otsu, 1979). An optimal threshold separating the foreground (oyster) from the background (conveyor belt) is calculated so that their combined spread (intra-class variance) is minimal (Otsu, 1979). This algorithm assumes that the image to be binarized contains two major classes of pixels (foreground and background) and the oyster image shown in Fig. 2(a) meets this requirement.