which typically exhibits 2 prominent peaks. The uppermost peak in the right
corresponds to the background pixels, while the second highest peak in the left corresponds to
the foreground regions, including skin regions. Based on the peak value and its width, adaptive
threshold values [Cr1, Cr2] and [Cb1, Cb2] can be selected as the intersections of probability
distribution functions in a mixture of Gaussians whose parameters can be estimated using an EM
algorithm. Then all pixels can be classified to have skin tone if its values (Cr, Cb) fall within the
ranges, i.e. and . Figure 14(b) &Figure 14(e) illustrates the CbCr
color range that's used for threshold: the Cb lower threshold ( =107) is at the bottom and the
upper threshold ( =122) is at the top; the Cr lower threshold ( =138) is left and the upper
threshold ( =151) is right. The segmented results of Cb and Cr components with adaptive
histogram segmentation are shown in Figure 14(c) &Figure 14(f)