在对Maio与Maltoni于1997年提出的指纹特征灰度图直接提取算法进行分析的基础上，提出了一种改进的指纹特征提取算法，即在前景模板分割部分采用Canny算子和数学形态学相结合的方法；在终结点判定部分提出跟踪角度和灰度变化相结合的新方法；在滤波和去除伪节点等方面也进行了改进。实验证明，这些改进在很大程度上克服了原算法阈值过多，易提取出虚假脊线的问题。这样不仅使算法健壮性和准确性得到了很大的提高，而且更有利于实际应用。

Minutiae has been comsidered as the most distinctive feature of a fingerprint and thus widely used in finger reconition/verification.Instead of using those conventional extraction methods based on binarization and ridgeline thinning,D.Maio and D.Maltoni proposed a totally different approach to detect the minutiae directly in gray-scale images in 1997.In this approach minutiae were extracted based on ridge tracing directly in gray images,so it showed more robust performance by avoiding the errors introduced by binarization and thinning.However,there are also drawbacks of this approach,such as the difficulties to decide the 7 thresholds,inaccurate ridge ending determination and etc.In this paper,an approach with several important improvements on D.Maio and D.Maltoni's method is presented.A novel method based on canny operator and morphology is used for fingerprint foreground segmentation,and both ridge tracing angle and the change of gray-level are introduced into the stop criteria of ending point.Other improvements include the selection of a better filter,and a post-processing to eliminate the spurious ridgelines and false minutiae by considering the length of ridgeline and the local structure of ridgelines where minutiae are detected.The efficiency and robustness of the proposed algorithm have been shown in the experiments.