US 11,900,634 B2
Method for adaptively detecting chessboard sub-pixel level corner points
Wei Zhong, Liaoning (CN); Deyun Lv, Liaoning (CN); Weiqiang Kong, Liaoning (CN); Risheng Liu, Liaoning (CN); Xin Fan, Liaoning (CN); Zhongxuan Luo, Liaoning (CN); and Shengquan Li, Liaoning (CN)
Assigned to DALIAN UNIVERSITY OF TECHNOLOGY, Liaoning (CN); and PENG CHENG LABORATORY, Guangdong (CN)
Appl. No. 17/604,185
Filed by DALIAN UNIVERSITY OF TECHNOLOGY, Liaoning (CN); and PENG CHENG LABORATORY, Guangdong (CN)
PCT Filed Mar. 5, 2020, PCT No. PCT/CN2020/077959
§ 371(c)(1), (2) Date Oct. 15, 2021,
PCT Pub. No. WO2021/138990, PCT Pub. Date Jul. 15, 2021.
Claims priority of application No. 202010027812.0 (CN), filed on Jan. 10, 2020.
Prior Publication US 2022/0198712 A1, Jun. 23, 2022
Int. Cl. G06T 7/80 (2017.01); H04N 17/00 (2006.01); G06V 10/75 (2022.01)
CPC G06T 7/80 (2017.01) [G06V 10/75 (2022.01); H04N 17/002 (2013.01)] 5 Claims
OG exemplary drawing
 
1. A method for adaptively detecting chessboard sub-pixel level corner points, comprising the following steps:
1) setting marks: setting marks on a chessboard to mark position of an initial unit grid;
2) shooting an image: using a camera to collect an image of a chessboard calibration target, and conducting preliminary image processing;
3) detecting the marks: detecting pixel coordinates of the marks set in step 1) by a mark detection algorithm;
4) using the marks: calculating pixel coordinates of four corner points of the initial unit grid defined by the marks according to the pixel coordinates detected in step 3), calculating sub-pixel level corner point coordinates by iteration and conducting verification;
5) expanding outwards: calculating a homography matrix H according to the sub-pixel level corner point coordinates of the four corner points in step 4) and world coordinates thereof in a world coordinate system; multiplying the homography matrix H with world coordinates of four corner points of an adjacent unit grid of the marked unit grid in the world coordinate system to calculate sub-pixel level corner point coordinates of the other two unknown corner points of the adjacent unit grid;
6) adaptively adjusting: counting side lengths of the adjacent unit grid obtained in the process of expanding outwards in step 5), and dynamically adjusting size of an iteration window for calculating sub-pixel level corner points to increase accuracy of sub-pixel level corner point detection.