Low-level feature extraction (including edge detection) - Feature Extraction and Image Processing - page 111

-1 0 1 -1 -2 -1

-2 0 2 0 0 0

-1 0 1 1 2 1

(a) -Mx (b) -My

Figure 4.12 Inverted templates for Sobel operator

in Figures 4.13 (a) and (b), respectively, where inverting the Mx template does not highlight
discontinuity at the corners. (The edge magnitude of the Sobel applied to the square is not
shown, but is similar to that derived by application of the Prewitt operator, Figure 4.9 (b).)

sobel_vec 0,0 , sobel_vec 0, 1
(a) Mx, My

- sobel_vec 0,0 , sobel_vec 0, 1
(b) - Mx, My

- sobel_vec 0,0 T , - sobel_vec 0, 1 T
(d) - My, - Mx

sobel_vec 0,0 T , sobel_vec 0, 1 T
(c) My, Mx

Figure 4.13 Alternative arrangements of edge direction