Fundamentals of Digital Image Processing - Control of Color Imaging Systems: Analysis and Design - page 61

HPF: The weight at the center is positive, and some or all of the filter weights

around the center weight are negative. This kind of filter often creates a

sharper image by accentuating the differences among pixels. The larger the
relative contribution of the negative taps of the filter, the sharper is the

filters are referred to as HPF because they generally
boost the high-frequency components of the image. Usually, the

filtered image. These

filter taps
in both LPF and HPF sum up to 1, so as to maintain the average brightness
of the output image at the same level as the input image. Following filters

are examples of common FIR filters used in image processing:

a. LPF

2
4

3
5

2
4

3
5

12221 11111

22422 11111

1
60

1
25

h ( n, m ) ¼

, h ( n, m ) ¼ ,

24842 11111

22422 11111

12221 11111

2 3

11211

4 5

12321

1
45

h ( n, m ) ¼ 23532

12321

11211

b. HPF

2
4

3
5

þ 1 2 þ 4 2 þ 1

2 þ 4 8 þ 4 2

h ( n, m ) ¼ þ 4 8 3 8 þ 4

2 þ 4 8 þ 4 2

þ 1 2 þ 4 2 þ 1

2
4

3
5

1 1 1 1 1

1 1 1 1 1

1
4

h ( n, m ) ¼ 1 1 8 1 1

1 1 1 1 1

1 1 1 1 1