中文摘要：

针对目前常用的图像清晰度评价方法存在的问题，分析了影响图像质量评价的因素，提出了基于图像对比度变化率的评价方法和基于自相关原理的评价函数改进算法，有效地避免了由于噪声干扰而出现的调焦函数曲线局部尖峰现象。实验结果表明，本文提出的评价函数的调焦曲线具有调焦性能好、抗干扰能力强和实时性好等优点。

英文摘要：

Aimed at the existent problems of the common image definition evaluation methods, the factors affecting image evaluation quality are analyzed, and an evaluation method based on the variety of image gray contrast and an improved algorithm of the image definition function based on autocorrelation are presented. The two methods effectively avoid the local peaks of the focusing curves caused by the noise disturbance. Experimental results indicate that the focusing curves of their evaluation functions have good focusing performance, the stronger antidisturbance and the better real time characterics.