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Citation Information : International Journal of Advanced Network, Monitoring and Controls. Volume 6, Issue 1, Pages 11-17, DOI: https://doi.org/10.21307/ijanmc-2021-002
License : (CC-BY-NC-ND 4.0)
Published Online: 19-April-2021
Periocular recognition technology is a biometric recognition technology widely used in identity verification. Because of its high precision, high ease of use and high security, Periocular recognition has a broad application prospect and scientific research value. In order to solve the problem of angular rotation of eyes in practical application, this paper proposes a deep learning periocular recognition method based on multi-angle data augmentation. The method is to rotate the original data set from small angle to large angle, so that the amount of data is expanded to 7 times of the original, and the diversity of data is increased at the same time. The InceptionV3 network and MobileNetV2 lightweight network are used for experimental verification respectively, and good results are obtained from multi-angle tests, indicating that the proposed method can improve the generalization ability of the model and has good robustness.
Identity identification is a basic problem in social life , which is not only closely related to the interests of individuals, but also affected national security and social stability. This paper studies the periocular recognition technology based on deep learning, which is to use the image of the eye area to identify the identity of people. Due to the high precision, high ease of use and high security of the eye circumference , it is easy to obtain eye images, analyze various information of the eye region, and integrate their respective characteristics to achieve accurate, rapid and robust identification. Periocular recognition has important application value and theoretical value.
Research on periocular recognition started late, and Park  initially proposed that eye peripheral area could be used for identity recognition. In the following studies, they gradually found that the periocular recognition system performed better, but its performance was not stable, due to illumination and blurring, resulting in less texture information. Many researchers had designed different periocular recognition systems for this kind of problem. Kumar  had developed various biometric recognition systems using different feature sets and different classifiers to identify subjects by using some reliable segmentation methods, efficient feature extraction methods and various classifiers or classifier integration. In 2017, a hybrid method based on transformation, structure and statistics, namely deep convolutional neural networks (CNNs), was proposed by Proenca and was also used to build periocular recognition systems. At the same time, Canadian professor Hugo. Proenca  also proposed to use neural network to process the human eye areas outside the eye, and to take the features extracted from these areas as a mode of identity recognition and attribute recognition.
In order to solve the problem of angular rotation of eyes in practical application, this paper proposes a deep learning periocular recognition method based on multi-angle data augmentation. The method is to rotate the original data set from small angle to large angle, so that the data volume is expanded to 7 times of the original, and the diversity of data is increased. InceptionV3 network and MobileNetV2 lightweight network are used for experimental verification respectively, and good results are obtained, indicating the feasibility of the proposed method.
The periocular recognition method based on deep learning in this paper is divided into deep neural network training and testing, as shown in figure 1. The training part of the network including the preparation of training data, data normalization, pre-processing operations, data enhancement, as well as the construction of the network, network parameters setting and adjustment. In the test part, the test image data can be input into the trained network to obtain the classification and recognition results.
The data enhancement method in this paper increases the number of samples, makes the data more diverse, and improves the generalization ability of the model. This method also enhances the robustness of the model and increases the practicability of the system by multi-angle and large-angle rotation of the eye image in the original database. The convolutional network adopts InceptionV3 network and MobileNetV2 lightweight network to carry out convolutional operation to extract features, train them separately, and obtain two recognition models. The recognition results of the two CNN models  are obtained through experiments.
Inception module is proposed to solve the problem that the difference in image content cannot effectively extract image information. The core is to split the layered network convolution kernel into different size convolution kernels, such as 3×3 convolution kernels split into ×1,3×3 convolution kernel, increases the size of the output network layer, such as 30×30, step size is 1, use 3×3 convolution kernel, without filling, the output image size is 28×28, If 1×1 and 3×3 convolution kernels are used to extract image information, the output depth map size is 30×30 and 28×28, and the acquired image information is richer than a single convolution kernel.
The InceptionV3 network architecture  consists of 11 Inception modules with a total of 46 layers. The package contains a total of 96 convolution layers. Table I below shows the overall structure of the InceptionV3 network model. Since Google InceptionV3 is relatively complex and the raw approach to building is resource- intensive, using the TensorFlow Slim tool can greatly reduce the amount of code needed to design InceptionV3. So the TensorFlow Slim tool is used to help build the network.
In recent years, numerous researchers have put forward various lightweight network models successively, such as SqueeZenet, MobileNetV1 , ShufflenetV1 , ShufflenetV2 , and MobileNetV2 . In the above network architecture, the test results of MobileNetV2 and ShufflenetV2 models are relatively good. The MobileNetV2 model uses deep separable convolution, linear bottleneck and reverse residual structure to maintain a certain degree of accuracy while keeping the number of parameters and computational complexity low. MobileNetV2 draws lessons from the RESNET network in the MobileNetV1 model based design. MobileNetV1 is designed according to the conventional convolution neural network chain structure, such as VGGNet model is to pile up in the form of convolution layer to build a network model, therefore, to some extent, improved the accuracy, the innovation points of this model is that the standard separation convolution with depth, reduce the size of the model, to some extent, computational complexity has been reduced. In addition, two compression hyperparameters are used to further shrink the network. However, because of this, too many convolutional layers will cause the problem of gradient disappearance.
ResNet networks  have a great fluidity of information between layers due to the use of residual units. Therefore, MobileNetV2 uses the deep separable convolution base of MobileNetV1 and ResNet’s residual unit for reference. MobileNetV2 network introduces a linear bottleneck structure and combines the reverse residual structure to complete improvements in these two aspects.
Table II shows the concrete implementation structure of the core building block of MobileNetV2, which is based on the Depth Separable Convolution Block of Reverse Residual, changing the number of input characteristic channels from N to M, where S represents the step size and T represents the expansion rate. A 1×1 convolution layer was added in front of the deep separable convolution layer, and the nonlinear activation function behind the point-by-point convolution layer was deleted to change the nonlinearity into linearity. Finally, in order to realize the subsampling, the scheme adopted is to set the step size parameter in the deep convolution.
MobileNetV2 overall network structure as shown in table III, every row describes one or more than one layer of the same sequence of loop n times, all sequence of layers have the same output channel number c, the sequence of the first layer step for s, residual layer of step 1, all the size of the space convolution kernels are the specifications of the 3 x 3, expansion ratio t always used the input characteristics described in table II. The MobileNetV2 model has an initial full convolutional layer of 32 convolutional cores, and then 17 reverse residual bottleneck modules are connected. The nonlinear activation function adopts ReLu6 with good robustness in the calculation with low precision, and the size selection of convolutional cores is 3×3.
In the process of neural network training, the stability of the model is proportional to the robustness, the number, and diversity of the training set data. However, the quality of the actual eye image acquisition may be poor. Therefore, the eye image in the original database is rotated from multiple angles to make the original database more diverse . At the same time, after the multi-angle rotation expansion, the problem of an insufficient number of eye images in the original data set is also solved, so as to improve the stability of the neural network training process. The schematic diagram of a partial processing of the eye peripheral sample is shown in Figure 2 to 7. The eye peripheral sample is rotated at 30°, 60°, 90°, 120°, 150°, and 180° respectively. Without the above method, in real life, if the user is slightly tilted or the angle of the device changes, the model will not be able to correctly recognize and judge, resulting in wrong recognition results. This will greatly affect the robustness of the model.
After rotation of 30°, 60°, 90°, 120°, 150° and 180°, the data volume of each group was amplified 6 times. Before the training set, each group had 6 pieces, and after amplification, each group had 42 pieces. Before amplification, the verification set and test set were 2 pieces in each group, and after amplification, 14 pieces in each group. The total number of data sets is 42, 000.
The experiment in this paper is carried out under Linux Ubuntu 16. 04 system, using NVIDIA GeForce RTX2080Ti ×4 graphics card, Intel Xeon Gold 6254×2 CPU, 128G memory, 960G SSD hard disk +8TB mechanical hard disk. GPU acceleration is used to increase computing efficiency and speed, and CUDA10. 0 is configured. The Python environment is version 3. 6. 5, with TensorFlow as a neural network framework .
The eye peripheralr data set used in this experiment is the CASIA-IRIS-Thousand periocular image in the IRIS database CASIA-IRIS 4. 0 of Chinese Academy of Sciences. In this group, there are a total of about 1000 people’s eyes and a total of 20, 000 eyes. The eyes of about 500 people were selected. Table IV shows the sample distribution of the experimental eye peripheral data set. As shown in Figure 8, the partial eye peripheral sample of 000L category in the eye peripheral data set is shown.
After the above data augmentation, the sample of the data set changed to the eye peripheral data set amplified by rotation, as shown in Table V. 30°, 60°, 90°, 120°, 150° and 180° image datas are added in the training set, verification set and test set. Training, validation and testing experiments are performed on the amplified eye peripheral data set.
After the eye peripheralr data set is prepared, specific experimental parameters are set, as shown in Table VI: The maximum number of steps is set to 20000 rounds, the batch size is set to 24 pieces, the learning rate decay type indicates whether the learning rate drops automatically, which is set to fixed, the learning rat is set to 0. 001, RMSProp is selected by the optimizer and weight decay of all parameters in the model is set to 0. 00004. As shown in figure 9, in the training process of the periocular recognition model based on the InpetionV3 network on the eye peripheralr data training set, its loss function decreased rapidly from the beginning of training to 5000 rounds, after which the loss function value tended to be flat.
After model training, validation set is used to verify the model. The verified accuracy rate is 98%. Finally, all the samples around the eyes of the test set are tested and the accuracy rate is 98%. It can be seen that the rotating samples with small and large angles, such as 30°, 60°, 90°, 120°, 150° and 180°, can be well recognized.
MobileNetV2 is used as the recognition method of Convolutional Neural Network and InceptionV3 network. The eye peripheral data sets are all expanded eye peripheral images. A total of 1000 groups of eye peripheral samples, 42 samples for each group, 42, 000 training sets, 14, 000 verification sets and 14, 000 test sets.
The experimental parameters of the MobileNetV2 lightweight network model are set as Table VII. The maximum number of steps is set to 100000 rounds, the batch size is set to 32, the learning rate decay type indicates whether the bearning rate automatically drops, which is set to fixed, and the learning rate is set to 0. 001. RMSProp is selected by the optimizer and weight decay is set to 0. 00004 for all parameters in the model. As shown in figure 10, in the periocular recognition model based on the MobileNetV2 lightweight network, in the training process of the training set using the eye peripheralr data, the change of its loss function drops sharply at the beginning, but with the progress of training, when the iteration reaches 20000 rounds, the loss function becomes flat.
The verification accuracy of the MobileNetV2 lightweight network model is 98. 21%. The validation accuracy of the IncpetionV3 network model is 98. 55%. After the training, the model is generated. The file size generated by the IncpetionV3 network model is 93MB, and the MobileNetV2 lightweight network model is 24MB. The MobileNetV2 lightweight network model is 3. 8 times smaller than the incpetionV3 network model when the verification accuracy is only 0. 3% lower. Therefore, the periocular recognition based on lightweight convolutional neural network model is feasible.
The same method is used to test the test set. The test set samples are rotated from multiple angles to test the robustness of the model. After the rotation of the test set, the model is still able to be recognized normally. The accuracy of the IncpetionV3 network model test is 98. 5%, and the MobileNetV2 lightweight model test is 98. 4%.
The eye images of the test set are tested on the two models respectively. As shown in figure 11, when testing the samples belonging to 302R, models with or without glasses can be correctly identified and the category of the tested samples can be correctly output.
It can be found from the eye samples that failed in the test, as shown in figure 12, that the feature information of the eye can no longer be accurately extracted due to a large amount of specular reflection interference. In fact, such samples do not meet the conditions of sample collection, which will have a great impact on the recognition accuracy of the model. However, the accuracy of the IncpetionV3 network model test is 98. 5%, and the MobileNetV2 lightweight model test is 98. 4%, even when large specular interference samples are included. Therefore, it can be concluded that the model in this paper still has a good recognition effect under the interference of such factors.
Follow-up, the eye images with specular reflection that has affected the image feature information in the test set are removed. The remaining samples are being tested. The accuracy of the IncpetionV3 network model test is 99. 8%, and the MobileNetV2 test is 99. 4%. It is concluded that the accuracy of both the traditional model and the lightweight model are improved when the image samples with great influence of mirror radiation are removed.
This paper mainly studies the periocular recognition technology based on deep learning, and uses the convolutional neural network InceptionV3 model to take the eye circle image as the input of the model, greatly shortening the steps of the entire recognition process. In fact, there are few angular rotation of eyes, so the original data can be more diversified by enhancing the eye image in the original database and carrying out multi-angle rotation. Then, according to the demand of mobile terminal, the application of lightweight model MobileNetV2 is proposed, which is used as the feature extraction classification architecture, and the periocular recognition technology based on lightweight convolutional neural network model is obtained. Experimental results show that both models can achieve satisfactory results after multi-angle data augmentation.