Tool to extract contour from a image using micro Convex Hull System (microCHSys).
GitHub: https://github.com/YujiSODE/microCHSys
Copyright (c) 2023-2025 Yuji SODE <yuji.sode@gmail.com>
This software is released under the MIT License.
See LICENSE or http://opensource.org/licenses/mit-license.php
Figure 1. Image to show the algorithm in APNG.
Moore neighborhood: c0 and c1 to c8.
[c1|c2|c3]
[c4|c0|c5]
[c6|c7|c8]
8-bit patterns in the micro Convex Hull system, when c0 is in a convex hull excluding its apices.
[when c0 = 1 and linear]
B = B129 B = B66 B = B36 B = B24
B: 0b10000001, B: 0b01000010, B: 0b00100100, B: 0b00011000
100__________ 010__________ 001__________ 000__________
010__________, 010__________, 010__________, 111__________
001__________ 010__________ 100__________ 000__________
[when c0 = 1 and nonlinear]
B = B162 B = B140 B = B69 B = B49
B: 0b10100010, B: 0b10001100, B: 0b01000101, B: 0b00110001
101__________ 100__________ 010__________ 001__________
010__________, 011__________, 010__________, 110__________,
010__________ 100__________ 101__________ 001__________
B = B81 B = B76 B = B138 B = B50
B: 0b01010001, B: 0b01001100, B: 0b10001010, B: 0b00110010
010__________ 010__________ 100__________ 001__________
110__________, 011__________, 011__________, 110__________
001__________ 100__________ 010__________ 010__________
[when c0 = 1 and areal]
B = B0
B: 0b00000000
000__________
010__________
000__________
B = c0;
ifB = B&B129^B129&&B&B66^B66&&B&B36^B36&&B&B24^B24&&B&B162^B162&&B&B140^B140&&B&B69^B69&&B&B49^B49&&B&B81^B81&&B&B76^B76&&B&B138^B138&&B&B50^B50&&B^B0;
if (ifB > 0) {
/* a given cell is not in the convex hull */
B = 1;
} else {
/*a given cell is in the convex hull */
B = 0;
}