Figure 4.19(b) shows the result of filtering Fig. 4.19(a) with a Butterworth highpass filter of order 2, and a value of Do equal to 5% of the vertical dimension of the padded image. Highpass filtering is not overly sensitive to the value of D0, as long as the radius of the filter is not so small that frequencies near the origin of the transform are passed .As expected ,filtered result is rather featureless, but it shows faintly the principal edges in the image .The advantage of high -emphasis filtering (with a = 0.5 and b = 2.0 in this case) is shown in the image of Fig. 4.19(c), in which the gray-level tonality due to the low-frequency components was retained. The following sequence of commands was used to generate the processed images in Fig. 4.19, where f denotes the input image the last command generated Fig. 4.19(d)]: