The Research Of Fingerprint Image Preprocessing Algorithm

Fingerprint recognition techniques become one of the most extensive identification and recognition techniques currently because its invariability. It is used broad in AFTS system, the control of gate system, computer safety system, network safety system and check on work attendance system etc. The fingerprint image preprocessing is the first step of automatic fingerprint identification system. Its quality affects directly the result of automatic identification system.Based on a lot of experiments, using technology of image processing and pattern recognition, the theory and methods of automatic identification are investigated and the automatic fingerprint preprocessing identification system is developed. At the same time, the key problems are discussed and some new methods are presented aiming at the status now in this field. The main contents are fingerprint image segmentation, minutiae extraction, thinning etc. The main jobs are as follows:(1)A fingerprint image segmentation algorithm based on the frequency of gray levels and 12-directional image is presented. The threshold can be selected naturally according to the image in this method and the difficulties in selecting the threshold are avoided. The fingerprint images with any difference in ridge and vale gray levels can all be segmented accurately. Experiments show that the method is 5.7875% lower in p error than squares difference and5.6625% lower in p error than directional image method. Moreover, the method is more robust because the difference of ridge and vale gray levels, orientation information isn't rigorous.(2)The method of ridges extraction is studied by experiments and amelioration. The direction of current block is changed according to the direction around the block, because the variety of fingerprint image direction is smooth. The eight-direction smoothing and enhancing filter are also proposed. As a result, the ridges can be extracted correctly.(3)The method of fingerprint image thinning is researched. Erasing the current point is decided according to the eight points around the current point. This method is simple and the results of thinning are very ideal.