Pretreatment Of The Fingerprint Image Based On Gray-scale Characteristics

In practice, due to kinds of cause, a 10 percentage of acquired fingerprint images are of poor quality by fingerprint image collecting in the system of automated finger identification. It's hard to extract the minutia from the poor quality fingerprint, and also the accuracy of minutia is affected. In order to ensure that the performance of the quality of input fingerprint image, a series of processes are needed to enhance the quality of fingerprint image.The paper discussed the fingerprint image preprocessing. The main research are as following: In the step of the segmentation, after analysis the method of segmentation based on gray-scale statistic, the segmentation use the ratio of the adaptive average value and standard deviation as the threshold of standard and then import the boundary of tracking after discussing the relation of remain region and effective region. And then the fingerprint enhancement is discussed from the side of direction computation and process of filtering, after comparing some methods of directional image computation, an improved method is proposed based on joint cutting method, designing a set of directional template to filter the fingerprint image. The set of methods can enhance the quality of fingerprint image effectively. After comparing and analyzing some methods of binarization and thinning, locally adaptive thresholding is chosen to binarize the enhanced image, and combining the quick thinning algorithm and improved OPTA thinning for the process of thinning.Experiments show that the methods of preprocessing in this paper have good results, which have effectively divided foreground form the fingerprint image and computed direction of fingerprint under the circumstance of voice. And after enhancement, the information on the ridgeline is effectively enhanced, while the vertical is weakened. The skeleton after thinning is convenient to extracting character form it.