Chapter 21
Image Manipulation
Like sounds, digital images are discretized versions of their analog coun-
terparts. Regular samples of color (instead of air pressure) are stored in a
two-dimensional grid (instead of a one-dimensional array). Access to these
samples allows us to change them in a variety of ways.
The following program requires image.py from Listing 24.3 to be in the same
folder or directory.
Listing 21.1: Two-Tone Image
1 # twotone.py
2
3 from image import ImagePPM
4
5 def luminance(c):
6 r, g, b = c
7 return 0.2
*
r + 0.7
*
g + 0.1
*
b
8
9 def twotone(c, bright, cutoff, dark):
10 return bright if luminance(c) > cutoff else dark
11
12 def f(c):
13 return ...
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