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1. End-to-end Off-angle Iris Recognition Using CNN Based Iris Segmentation

   Jalilian, E; Karakaya, M; Uhl, A. (January 2020, 2020 International Conference of the Biometrics Special Interest Group (BIOSIG))

   null (Ed.)

   While deep learning techniques are increasingly becoming a tool of choice for iris segmentation, yet there is no comprehensive recognition framework dedicated for off-angle iris recognition using such modules. In this work, we investigate the effect of different gaze-angles on the CNN based off-angle iris segmentations, and their recognition performance, introducing an improvement scheme to compensate for some segmentation degradations caused by the off-angle distortions. Also, we propose an off-angle parameterization algorithm to re-project the off-angle images back to frontal view. Taking benefit of these, we further investigate if: (i) improving the segmentation outputs and/or correcting the iris images before or after the segmentation, can compensate for off-angle distortions, or (ii) the generalization capability of the network can be improved, by training it on iris images of different gaze-angles. In each experimental step, segmentation accuracy and the recognition performance are evaluated, and the results are analyzed and compared. 

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2. CNN‐based off‐angle iris segmentation and recognition

   https://doi.org/10.1049/bme2.12052  

   Jalilian, Ehsaneddin; Karakaya, Mahmut; Uhl, Andreas (June 2021, IET Biometrics)

   null (Ed.)

   Accurate segmentation and parameterization of the iris in eye images still remain a significant challenge for achieving robust iris recognition, especially in off‐angle images captured in less constrained environments. While deep learning techniques (i.e. segmentation‐based convolutional neural networks (CNNs)) are increasingly being used to address this problem, there is a significant lack of information about the mechanism of the related distortions affecting the performance of these networks and no comprehensive recognition framework is dedicated, in particular, to off‐angle iris recognition using such modules. In this work, the general effect of different gaze angles on ocular biometrics is discussed, and the findings are then related to the CNN‐based off‐angle iris segmentation results and the subsequent recognition performance. An improvement scheme is also introduced to compensate for some segmentation degradations caused by the off‐angle distortions, and a new gaze‐angle estimation and parameterization module is further proposed to estimate and re‐project (correct) the offangle iris images back to frontal view. Taking benefit of these, several approaches (pipelines) are formulated to configure an end‐to‐end framework for the CNN‐based offangle iris segmentation and recognition. Within the framework of these approaches, a series of experiments is carried out to determine whether (i) improving the segmentation outputs and/or correcting the output iris images before or after the segmentation can compensate for some off‐angle distortions, (ii) a CNN trained on frontal eye images is capable of detecting and extracting the learnt features on the corrected images, or (iii) the generalisation capability of the network can be improved by training it on iris images of different gaze angles. Finally, the recognition performance of the selected approach is compared against some state‐of‐the‐art off‐angle iris recognition algorithms. 

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3. Off-angle iris recognition using single and multiple deep learning frameworks

   https://doi.org/10.1117/12.2662862  

   Chavarro, David; Karakaya, Mahmut (June 2023, Multimodal Image Exploitation and Learning)

   Agaian, Sos S.; DelMarco, Stephen P.; Asari, Vijayan K. (Ed.)

   Iris recognition is a widely used biometric technology that has high accuracy and reliability in well-controlled environments. However, the recognition accuracy can significantly degrade in non-ideal scenarios, such as off-angle iris images. To address these challenges, deep learning frameworks have been proposed to identify subjects through their off-angle iris images. Traditional CNN-based iris recognition systems train a single deep network using multiple off-angle iris image of the same subject to extract the gaze invariant features and test incoming off-angle images with this single network to classify it into same subject class. In another approach, multiple shallow networks are trained for each gaze angle that will be the experts for specific gaze angles. When testing an off-angle iris image, we first estimate the gaze angle and feed the probe image to its corresponding network for recognition. In this paper, we present an analysis of the performance of both single and multimodal deep learning frameworks to identify subjects through their off-angle iris images. Specifically, we compare the performance of a single AlexNet with multiple SqueezeNet models. SqueezeNet is a variation of the AlexNet that uses 50x fewer parameters and is optimized for devices with limited computational resources. Multi-model approach using multiple shallow networks, where each network is an expert for a specific gaze angle. Our experiments are conducted on an off-angle iris dataset consisting of 100 subjects captured at 10-degree intervals between -50 to +50 degrees. The results indicate that angles that are more distant from the trained angles have lower model accuracy than the angles that are closer to the trained gaze angle. Our findings suggest that the use of SqueezeNet, which requires fewer parameters than AlexNet, can enable iris recognition on devices with limited computational resources while maintaining accuracy. Overall, the results of this study can contribute to the development of more robust iris recognition systems that can perform well in non-ideal scenarios. 

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4. Fragile Bits in Off-angle Iris Recognition

   https://doi.org/10.1109/IWBF50991.2021.9465098  

   Karakaya, Mahmut (May 2021, 2021 IEEE International Workshop on Biometrics and Forensics)

   null (Ed.)

   As an emerging biometric research, standoff iris recognition systems focus on recognition of non-cooperative subjects in much less constrained environments where their captured images are likely to be non-ideal including being off-angle. Iris biometrics convert unwrapped iris textures into binary iris codes to compare them with other saved codes by measuring their Hamming Distances. The similarity calculation assumes an equal contribution of each individual pixel in iris codes. However, previous studies showed that some pixels (aka. fragile bits) are more error prone than others even in frontal iris images. In addition, off-angle iris images are affected by several challenging factors including corneal refraction and limbus occlusion. These challenges in off-angle images also increase the fragility of bits in iris codes. This paper first presents the pixel inconsistency in iris codes of off-angle images using elliptical segmentation and normalization. The pixel fragility is a result of iris codes warping due to the refraction of light in cornea and occlusion of iris texture at limbus. As another contribution, we propose to identify these fragile pixels in iris codes using edge detection and eliminating them in Hamming distance calculation by masking these fragile bits. Based on the results, the proposed method improves the recognition performance in off-angle iris images where the average genuine Hamming distance score reduced from 0.3082 to 0.1244 and the equal error rate is lowered 19%. 

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5. Gaze-angle Impact on Iris Segmentation using CNNs

   https://doi.org/10.1109/BTAS46853.2019.9185970  

   Jalilian, E.; Uhl, A.; Karakaya, M. (October 2019, IEEE International Conference on Biometrics Theory Applications and Systems)

   Emerging standoff iris recognition systems operate under unconstrained conditions and the iris images captured by these systems are more subject to off-angle acquisition distortions. While deep learning techniques (e.g. convolutional neural networks (CNNs)) are increasingly becoming a tool of choice for iris segmentation tasks, yet there is a significant lack of information about how these distortions affect the performance of such networks. In this work, we thoroughly discuss the general effect of different gaze angles on ocular biometrics and relate the findings to off-angle iris segmentation using CNNs. In particular, we conduct systematical analysis on the impact of different gaze angles on segmentation performance of two CNNs with different architectures. The networks’ performance turns out to have a direct relation to the closeness of gaze-angles in the training and testing images, and it declines as the gaze angles diverge. We further investigate the effect of (i) increasing the quantity of iris training data in case of gaze angles in training and test data match, and (ii) considering iris training data consisting of several distinct gaze-angles (we obtain promising results using the second configuration). Finally, we compare our results to those of some classical iris segmentation algorithms, where the CNNs are found to outperform the classical algorithms. 

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