Research on CMOS Image Preprocess Methods for Auto-Focusing System

The image preprocess is the first course after image sampling in an auto-focusing system based on the definition recognition technology. The image preprocess includes converting image data format, filtering for noise removal, reducing ray disturbing and so on. Considering the features of CMOS sensor´s imaging, the paper discusses the image quantization method and the image format converting method, and analyzes the effects of applying the linear transform and histogram equilibrium of image gray value for the auto-focusing system with a CMOS image sensor. At the last, the discussion on the filtering method for noise removal was made. And the mean filter of neighborhoods and the median filter are optional to reduce positive noise. But according to the result of the experiments, the former will weaken the image edge and will not be good for reducing noise of spiced salts. The latter has a good effect to reduce positive noise and to conserve the image edge. As for the reduction of multiple noises, the homomorphic filter can be chosen, which separates signal and noise, filters noise, and then restores original signal. The filter´s effect is determined by its design.