Keywords: focus value curve, focus measure, auto focus, sub-window, best-focused lens position
Received June 10, 2008; revised October 27, 2008; accepted November 12, 2008.
Communicated by H. Y. Mark Liao.
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LI-CHENG CHIU AND CHIOU-SHANN FUH
Department of Computer Science and Information Engineering
National Taiwan University
Taipei, 106 Taiwan
This paper models focus value curve from point light source to focus measure calculation.
This model shows that focus values of one object in a scene will form a single
peak bell-shaped curve in camera. Our proposed auto focus method adopts this model
with focus sub-window selection to predict the peak of focus value curve. Accurate prediction
for the best-focused lens position will greatly shorten search time. Besides, the
period of focus value feedback from camera chip is further considered to determine lens
step in one period to optimize practical time consumption. Through experiments, our
model for focus value curve is correct and proposed auto focus method efficiently shortens
overall search time.
Received June 10, 2008; revised October 27, 2008; accepted November 12, 2008.
Communicated by H. Y. Mark Liao.