Digital Image Processing Applications In The Auto-focus System

Auto-focusing technology is a crucial technology in the robot vision and digital video frequency system. At the same time it is also an absolutely necessary crucial technology in modern optics imaging system. With rapid development of science and technology, people think much more of auto-focusing issue. Especially for some amateur users, focusing needs long time to complete, so it wastes time and brings fatigue. Now auto-focusing technology makes focusing easy, only for a press. The intelligent focusing is most important in many ways of completing auto-focusing. It has an advantage of high speed and high precision.From the latter years of 80's, domestic and foreign scholars have made much research in the auto-focusing issue. Now with absolutely digital processing technology, there are four classes in traditional image definition clarity-evaluation-functions. They are gray-level changed function, entropy function, gradient function, frequency domain function. But traditional image definition clarity-evaluation-functions have two disadvantages. One is precise focusing factor, the other is high speed focusing factor. If image definition clarity-evaluation-functions is ideal, they should possess no departure and single peak value trait, display the polarity of out-of-focus and take on enough big SNR (Signal-to-Noise Ratio).Based on Fourier optical theory, PSF (point spread function) and OTF(optical transfer function) are introduced. Then the mechanism why digital image is focus in optics imaging system is also analyzed. Thus the arithmetic is naturally achieved.The clarity-evaluation-function of out-of-focus blurred image is a key factor for auto-focusing by using digital image processing and the accuracy and efficiency of the function need to be improved. It is found that the blurred image has large amount of pixels with low gradient while the focused image has obviously more pixels with high gradient than the blurred image after deep study of the gradients of various images. Therefore, we can threshold gradients in order to throw low gradients and remain high gradients. And then the advantages of focused image are obviously showed. A kind of...