Abstract:

To rapidly and accurately acquire a clear tongue image needs adjusting and controlling of the distance between camera and the tongue. This paper elaborated the factors that influence image quality such as clarity,light reflection scale,shade scale,illumination condition and focal length and the focusing method used in adjusting the position of lens and subject. Combined with the focus technology, this paper established a mathematical model of the relation of image quality and distance of lens and subject. The procedure of auto-focus was the acquisition of the maximum value of the focusing evaluation function employing the mountainclimb searching algorithm. Unlike the traditional mountain-climb searching algorithm which was apt to disturbed by the local extremum, introduced an algorithm that preprocessing each frame of image firstly and using the two step method of rough before precision, which effectively get rid of this disturbance. It has realized by using VC++6.0 program to automatically adjust the acquisition machine to acquire the best quality picture. Experiment results showed that this method was fast, precision, strongly anti-interference and other good characteristics.

Key words: auto-focus, conic fitting algorithm, mountain-climb searching algorithm, focusing evaluation function, image pre-processing