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32 Chapter 2 ■ Edge-Detection Techniques

No added noise σ= 3 σ= 9 σ= 18
SNR = 6 SNR = 2 SNR = 1

ET1-
Step edge
at j = 127,
delta = 18

ET2-
Step edge
at i = 127,
delta = 18

ET3-
Step edge
at i = j,
delta = 18

ET4-
2 part
stair, each
delta = 9

ET5-
3 part
stair, each
delta = 6

CHESS-real
sampled
image.

Figure 2.8: Standard test images for edge-detector evaluation. There are three step edges
and two stairs, plus a real sampled image; all have been subjected to normally distributed
zero mean noise with known standard deviations of 3, 9, and 18.