中文摘要：

指纹纹线的方向和频率是图像滤波的两个主要参数，梯度方向图算法可以得到较好的纹线方向，灰度频率场的算法受峰值计算的复杂性影响，容易造成滤波效果不好。把梯度方向场划分为不同的方向分量，在分量上对差分二值图像进行亚像素的纹线频率计算，最后合成到频率场中，使滤波效果得到了全面的提升．实验表明，亚像素频率的精确计算，能够显著提高识别系统的性能。

英文摘要：

Orientation and frequency are two main parameters for fingerprint filtering.With the gradient orientation field algorithm,preferable texture orientation field can be obtained.The grey frequency field is influenced significantly by the complexity of peak value calculation, resulting in unsatisfactory filtering results.This paper divides the gradient orientation filed into different components, calculates the sub-pixel texture frequency of the differential binary image in each of the components, and combines the sub-pixel frequency into a frequency field, improves the overall filtering results significantly.Experiments show that the accurate sub-pixel frequency calculation can improve the performance of Automated Fingerprint Identification Systam（AFIS） remarkably.