数字图像的清晰度评价一直是各类数字成像系统的一个关键问题，而在已有的一些的评价参数中，由于评价方法不同，均存在一些局限性，为此，针对图像的清晰程度提出一种新的评价方法，目的在于能够快速、准确地评价数字图像的清晰度。该评价方法评价参数可通过改进边缘锐度算法(EAV)得到，然后与机测MTF值的变化趋势一起做曲线回归分析，以便和其他传统清晰度评价参数做对比。通过上百幅各类数字图像的测试，结果表明，该评价参数与数字成像系统的MTF值变化有着很好的正相关关系，其不仅能够更准确地反应数字图像清晰度变化的趋势，而且便于简捷、快速地应用于各类数字图像的清晰度评价。

Evaluation of definition for gray scale digital image is an important aspect of digital imaging system. Thus, in order to evaluate the definition of a gray scale image accurately and effectively, we present a new approach based on EVA method which, while retaining important features of existing method, overcomes some of their limitation. With curvilinear regression analysis we can prove that the result of the new approach is high correlation with MTF measured by optical instrument, in other words, the new method is sensitive to the change of image definition. When compared with traditional method, the result of analysis can also show that the new method is better than traditional method, such as entropy, to assess gray scale digital image definition. Experiments using hundreds of many kinds of gray scale digital image and the result of this new approach is well accurate to the change of definition of digital image. Form these we can also draw a conclusion that the new approach can be well applied to many kinds of gray scale digital image accurately and effectively.