Objective Palm vein recognition takes advantage the stability and uniqueness of human palm vein distribution for identification.The palm vein is hidden under the epidermis and cannot be photographed under visible light,and the replication of its complex structure presents difficulty.A severed palm or corpse fails certification because blood has stopped flowing,which makes palm vein recognition suitable for high-security applications.The noncontact collection in an open environment is more popular than the traditional collection method of placing the palm on a fixed bolt in the collection box.However,the opacity,inhomogeneity,and anisotropy of the skin tissue covering the palm vein cause scattering of near-infrared light.The visible light in open environments aggravates scattering and increases noise,which result in vague palm vein imaging in some people.The noncontact acquisition method increases the intraclass difference of the same sample increase due to rotation,translation,scaling,and illumination in multiple shots.The above difficulties make recog-nition challenging.A method based on unsupervised convolutional neural network was studied with aim of addressing such difficulties.Method Given that this paper requires a benchmark library to train the self-built network,a palm vein image library containing 600 images from 100 volunteers was established.Then,the program parameters were trained and adjusted using the self-built library.After several training adjustments,the optimal \and the trained network parameters were acquired.In image preprocessing,the region of interest(ROI)was extracted from all the palm vein images collected.First,the original palm vein image was denoised and binarized via low-pass filtering.Then,the palm contour was extracted via the dilation method in binary morphology.The obtained palm contour was refined into a single pixel,and the palm vein ROI was extracted using a method mentioned in literature.The extracted palm-vein ROI was adjusted based on the corre-sponding pixel size,and the mean was subtracted for normalization.A local region was extracted for each pixel in the pro-cessed ROI of the palm vein to ensure that it covers the entire ROI of the palm vein.In addition,all local regions are con-verted into vector forms.A filter of the principal component analysis was used to extract principal component information in the convolution layer to reduce the noise caused by visible light.The fixed-size Gabor filter was used to obtain prior knowl-edge on the multiscale adaptive Gabor filter to overcome the interferences resulting from image rotation,translation,scal-ing,and illumination changes on recognition and improve palm-vein stability features and recognition performance.Then,the amount of data was reduced by binarization.Finally,the adaptive K-nearest neighbors(Ada-KNN)variant classifier was used for classification and recognition.The Ada-KNN2 classifier uses heuristic learning method instead of neural net-work.With the use of density and distribution of the test point neighborhood,the specific k value suitable for the test point was determined using an artificial neural network to achieve efficient and accurate distinction between samples and solve the problem of the increased difference in the same sample image.In addition,unbalanced sample data are avoided,which a great influence on the results.Result Experimental findings show that this method can effectively increase the recognition accuracy compared with traditional and classical network methods.The equal error rates(EERs)of the three libraries were 0.289 9％,0.211 3％,and 0.158 6％,respectively.Compared with the traditional method that had the best effect on the three libraries during comparison,EER was reduced by 0.176 8％,2.466 5％,and 1.468 1％compared with the classical network method that had the best effect.EER decreased by 0.033 3％,0.233 3％,and 0.248 7％.The false rejection rate/false accept rate were 0.002 7/2.318 8,0.002 3/1.282 1,and 0.000 0/1.596 2.In addition,from the generated receiver operating characteristic curve,the advantages of the method in recognition performance can be observed more intuitively.It can distinguish and recognize similar images to a great extent and improve the overall recognition perfor-mance.The proposed method also effectively solves the problem of increased differences in similar images due to altera-tions in rotation,translation,scaling,and illumination during noncontact acquisition,which led to a decrease in the recog-nition performance.Conclusion The experimental findings underscore the effectiveness of the proposed method in addressing the aforementioned challenges.Nevertheless,the operational efficiency of this approach exhibits relative insufficiency.Conse-quently,further investigation and in-depth studies should be aimed at addressing this efficiency gap.Future research endeavors should cover strategies for the systematic enhancement of the operational efficiency without compromising the robustness and preci-sion of the recognition process.One pivotal area of exploration pertains to sample size expansion,which warrants a meticulous examination of methodologies to ensure the scalability of the proposed approach.Concurrently,optimization measures should be meticulously devised to fine tune operational aspects to achieve an optimal balance between efficiency and accuracy.
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