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《Optics and Precision Engineering》 2004-05
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Experimental research and analysis of automatic focusing function for imaging measurement

ZHAO Hui, BAO Ge-tang, TAO Wei (Department of Instrumentation Engineering, Shanghai Jiao Tong University, Shanghai 200030,China)  
Several general automatic focusing functions for imaging measurement are put forward, compared and analyzed in defail. The main parameters of automatic focusing, including sensitivity, consistency, stability and calculating speed, were tested and validated through a series of experiments under different conditions, such as different lighting or different background. The results of experiments show that in the background lighting, the gray functions all have better performance than others, the Variance function and the sum of gray-change function have a large focusing range, good linearity and low sensitivity, so they are propitious to focusing in large range with lower accuracy. The Laplacian and Tenengrad functions both have sharp peak, good sensitivity and small focusing range, which make them applicable to accurate focusing in small range. But in reflection lighting, only the Tenengrad and Brenner functions have fine single peak and low sensitivity. All of these focusing functions will be disabled when the complex backgrounds exist. So, when it comes to practical application, background lighting should be chosen instead of reflection lighting, also interference coming from background should be reduced to minimum level.
【CateGory Index】: TP391.41
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