To keep image captured by optical measuring system in focus, pixel-based auto-focusing is a long-standing topic in the literatures. Sharpness function is the mathematical description of image sharpness. It plays an important role for realizing robust auto-focusing of optical measuring system. In optical tracking measuring system, the size of moveable object image always is variational. Under this condition, the existing sharpness functions will not work well for autofocus system. In this paper, an efficient sharpness function based on the number of variable threshold gradients is proposed. This auto-focus algorithm calculates the number of gradients bigger than threshold, while threshold is variable according to image. By using this auto-focus algorithm to optical measuring system, the robust and reliability of autofocus system are improved. Practical applications illuminate the proposed approach is feasible and effective.

Date Published: 20 May 2009
PDF: 5 pages
Proc. SPIE 7283, 4th International Symposium on Advanced Optical Manufacturing and Testing Technologies: Optical Test and Measurement Technology and Equipment, 728344 (20 May 2009); doi: 10.1117/12.828802

Published in SPIE Proceedings Vol. 7283:
4th International Symposium on Advanced Optical Manufacturing and Testing Technologies: Optical Test and Measurement Technology and Equipment
Yudong Zhang; James C. Wyant; Robert A. Smythe; Hexin Wang, Editor(s)