高效、准确的图像清晰度评价是实现自动调焦的关键。在分析了现有图像清晰度评价方法优缺点的基础上，提出了一种基于图像区域对比度的清晰度评价新方法，建立和分析了评价函数的数学模型，并对航空摄像机采集的系列图像进行实验和仿真。与其他算法比较的结果表明：该方法具有精确度高、对比度明显等优点，能够应用于实际的图像清晰度评价和自动对焦中，克服了单纯依靠计算灰度差带来的不足，具有较高的实用性和可靠性。

The accurate and efficient evaluation of image definition is a critical step in automatic focusing. In the available evaluation methods, there are a variety of limitations due to different parameters used. After analyzing the advantages and disadvantages of existing methods for image clarity evaluation, a new evaluation method for image definition based on regional contrasting is proposed based on image analysis and statistics. The mathematical model is established and analyzed, and the experimental results are given. It is proved that, this evaluation method satisfies the basic tactic requirements, and has high sensitivity and reliability in automatic focusing.