Image Processing Reference
In-Depth Information
Figure 3.5
Median filtering in a 3 × 3 window. The median filter reduces the error on the first
pass but has little further effect on the second. While much of the noise is removed, the text is
damaged.
Figure 3.6
Optimum filtering. The results of applying the optimum filter within a 3
×
3 and 5
×
5 window are shown. They result in much lower errors than the median filters. The damage to
the text is much less than for the median filters in Fig. 3.5.
ing the error to 144 pixels. For comparison, the optimum filter in a 5 × 5 window
was also designed and applied. It had an error of just 23 pixels. The results of filter-
ing with these optimum filters are shown in Fig. 3.6.
In order to investigate why the optimum filter is so much better than the me-
dian, the filters implemented in a five-point cross will be analyzed. The results of
these filters are shown in Fig. 3.7. The optimum filter
ψ
opt
gives an error of 360 pix-
