Fundamentals of Digital Image Processing - Control of Color Imaging Systems: Analysis and Design - page 86

y ( n, m ) ¼ f ( n, m ) þ s ( n, m ) ( 2 : 142 )

The halftone image is obtained by quantizing y ( n, m ) to 1 bit, that is,

1 y ( n, m ) T

g ( n, m ) ¼ ( 2 : 143 )

0 otherwise

The threshold T for an 8 bit image is 126.
Equation 2.144 is a typical halftone pattern. This halftone pattern is repeated
periodically to generate a halftone screen s ( n, m ) of the same size as the original

continuous tone image f ( n, m ) .

2 3

52 44 36 124 132 140 148 156

4 5

60 4 28 116 200 228 236 164

68 12 20 108 212 252 244 172

76 84 92 100 204 196 188 180

Halftone pattern ¼ ( 2 : 144 )

132 140 148 156 52 44 36 124

200 228 236 164 60 4 28 116

212 252 244 172 68 12 20 108

204 196 188 180 76 84 92 100

is an example, the 512 512 LENA image shown in Figure 2.56 is the input to the

halftone algorithm shown in Figure 2.55. The halftone screen is ( n, m ) is shown in

Figure 2.57 and is generated using the halftone pattern shown in Equation 2.144. The
resulting halftone image is shown in Figure 2.58.
Another common halftoning technique is error diffusion technique discussed in
Section 2.10.1.

FIGURE 2.56 Original image.