Cancelling bias induced by correlation coefficient interpolation for sub-pixel image registration

• Published in: Measurement science & technology Vol. 24; no. 3; pp. 35404 - 1-10
• Main Authors: Cheng, Peng, Menq, Chia-Hsiang
• Format: Journal Article
• Language: English
• Published: IOP Publishing 01.03.2013
• Subjects: Bias; bias cancellation; Computational efficiency; Computer simulation; Correlation coefficients; digital image correlation; Fourier transform; Image registration; Interpolation; Real time; sub-pixel
• ISSN: 0957-0233; 1361-6501
• DOI: 10.1088/0957-0233/24/3/035404

Accurate sub-pixel image registration has many applications in precision engineering and manufacturing. Due to its computational efficiency, correlation-based sub-pixel image registration is especially useful for real-time applications. This paper presents a theoretical analysis of the bias induced by correlation coefficient interpolation, when employed to achieve two-dimensional sub-pixel registration resolution. An analytical model of bias in terms of true sub-pixel image shift is first derived according to the given reference image model. It is then used to establish an accurate bias map expressed explicitly in terms of sub-pixel image shift estimated from coefficient interpolation. This bias map is readily employed to eliminate the bias error and to significantly improve measurement accuracy for real-time applications. A bias cancellation scheme was implemented and verified by means of both computer simulation and experimental results. Specifically, sub-nanometre measurement precision was experimentally demonstrated using a microscopic vision system implemented for real-time motion tracking.