目的 指纹图像增强是自动指纹识别系统中的重要环节，是获取可靠的指纹细节特征的基础。为了弥补指纹图像的质量缺陷，实现对低质量指纹图像的有效增强，提出一种基于块质量评价和块频谱匹配滤波器的块频谱扩散指纹增强方法。方法 首先，基于块内点方向一致性参数，给出了块质量评价结果；然后，研究了复合窗口频谱扩散特性，完成了基于一次模糊K均值聚类、一阶自适应带宽的2维巴特沃斯带通滤波器和2维高斯窗的块频谱匹配滤波器设计；最后，依据块质量等级的高低，应用块频谱匹配滤波器对复合窗口的块频谱进行滤波增强。结果 选取FVC 2004指纹库中的大量指纹图像进行了实验，实验结果表明，该方法对高质量和低质量指纹图像均有良好的增强效果。结论 本文方法对指纹的脊线方向和频率等参数依赖较弱，拥有很强的容错能力。实验结果验证了该方法在指纹图像增强中的有效性，可适用于高质量和低质量的指纹图像增强。

Objective The enhancement of fingerprint plays an important role in automatic fingerprint identification system. It is the foundation that extracts fingerprint minutiae reliably. In order to make up for the defects of fingerprint image and enhance low quality fingerprint image effectively,this paper proposes a novel algorithm by using spectrum diffusion to enhancing the fingerprint image. The basic idea of the algorithm is to enhance the fingerprint by using block quality assessment and block spectrum matched filter in the frequency domain. Method First,the quality assessment result of block image is obtained according to the point direction coherence parameter. Second,this paper studies the diffusion characteristics of composite window spectrum,and then design out a block spectrum matched filter based on linear fuzzy k-means clustering and 2D Butterworth band-pass filter of one order adaptive bandwidth and two-dimensional Gaussian window. At last,the composite window spectrum is enhanced by block spectrum matched filter according to the block quality grade. Result Experiments on the database of FVC 2004 show that,compared with the previously proposed enhancement methods,the proposed method is more accurate and more robust against noise,and has a prominent effect on both low quality and high quality fingerprint image. Conclusion This paper presents a fingerprint enhancement using filter method of weak parameters dependencies in frequency domain. This method is of good fault tolerant. The experimental results show that both high quality and low quality fingerprint image can be enhanced effectively.