Rapid Automatic Lighting Control of a Mixed Light Source for Image Acquisition using Derivative Optimum Search Methods

¹ Smart Manufacturing Technology Group, KITECH, 35-3, HongCheon, IpJang, CheonAn, ChungNam, 331-825, South Korea
² UTRC, KAIST, 23, GuSung, YouSung, DaeJeon, 305-701, South Korea

^a e-mail: htkim@kitech.re.kr
^b e-mail: yong00@kaist.ac.kr
^c e-mail: stkim@kitech.re.kr
^d e-mail: jongseok@kitech.re.kr
^e e-mail: kcjin@kitech.re.kr
^f e-mail: memslee@kitech.re.kr

Abstract

Automatic lighting (auto-lighting) is a function that maximizes the image quality of a vision inspection system by adjusting the light intensity and color.In most inspection systems, a single color light source is used, and an equal step search is employed to determine the maximum image quality. However, when a mixed light source is used, the number of iterations becomes large, and therefore, a rapid search method must be applied to reduce their number. Derivative optimum search methods follow the tangential direction of a function and are usually faster than other methods. In this study, multi-dimensional forms of derivative optimum search methods are applied to obtain the maximum image quality considering a mixed-light source. The auto-lighting algorithms were derived from the steepest descent and conjugate gradient methods, which have N-size inputs of driving voltage and one output of image quality. Experiments in which the proposed algorithm was applied to semiconductor patterns showed that a reduced number of iterations is required to determine the locally maximized image quality.