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dynamic range and, in addition, detail amplified for human viewing as 
demonstrated by the set in Fig. 4 (a-f), and in Fig. 5 a,b. Note the 
simultaneous emergence of detail in both the bright and dark regions. 
These examples 
Fig. 4. 
A set of aerial images, (a, 
c, e), enhanced for higher 
visibility of detail: (b, d, 
f), with some detail lost in 
the printing process. A 
magnified patch of moiré 
pattern (g) is low pass 
filtered for spatial carrer 
suppression (h). Relative 3 
x 3 coefficients (Real, 
1983) from top to bottom on 
the right are: 
b d 
  
- 5-2 5.2 Q i5 0 
-2 3: -2 «5 pues 
-2 2 2 0-5 0 
f h 
  
2 -4 2 3 3 3 
-& 1 -4 3 58543 G h 
2 + 2% CE 
illustrate high pass spatial filtering. Low pass spatial filtering is usually 
employed for some forms of noise rejection. Fig. 4(g) is part of a magnified 
patch of moiré pattern exhibiting some horizontally oriented "noise" which 
results from the grating carrier frequency. Setting the filter coefficients 
to positive values, Fig. 4(h), is analogous to defocussing the image, thereby 
suppressing this carrier to some degree.