2.3.2. Parameter selection
The initial response of the pixel in ROI was determined by two parameters – the radius of the circular neighborhood rd and the intensity contrast threshold t, according to Eq. (8). In a gray-level image, the radius of the circular neighborhood rd is related to the maximum width of lines of interest, while the intensity contrast threshold t is defined as the standard deviation of ROI (Liu et al., 2007). In this study, marbling was extracted from digital color images or sample images instead of the gray-level image. Accordingly, the radius of the circular neighborhood rd was related to the maximum width of lines of interest among all three channels of the image. The intensity contrast threshold at each channel, ICTc, was defined by: