Figure 10 The left side shows very thick edges around the triangle and rectangle. The right side shows the result of eroding any 1 that has three 0 neighbors

00000000000000000000  00000000000000000000
00000001000000000000  00000000000000000000
00000011100000000000  00000001000000000000
00000111110000000000  00000011100000000000
00001110111000000000  00000100010000000000
00011100011100000000  00001100011000000000
00111111111110000000  00011110111100000000
01111111111111000000  00111111111110000000
11111111111111100000  00011111111111000000
00001111111111111100  00000111111111111000
00001111111111111100  00000111111111111000
00001111111111111100  00000111000000111000
00001110000000011100  00000110000000011000
00001110000000011100  00000100000000001000
00001110000000011100  00000110000000011000
00001111111111111100  00000110000000111000
00001111111111111100  00000111111111111000
00001111111111111100  00000000000000000000
00000000000000000000  00000000000000000000
00000000000000000000  00000000000000000000