Towards a Fast and Accurate Face Recognition System from Deep Representations

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The key components of a machine perception algorithm are feature extraction followed by classification or regression. The features representing the input data should have the following desirable properties: 1) they should contain the discriminative information required for accurate classification, 2) they should be robust and adaptive to several variations in the input data due to illumination, translation/rotation, resolution, and input noise, 3) they should lie on a simple manifold for easy classification or regression. Over the years, researchers have come up with various hand crafted techniques to extract meaningful features. However, these features do not

perform well for data collected in unconstrained settings due to large variations in appearance and other nuisance factors.

Recent developments in deep convolutional neural networks (DCNNs) have shown impressive performance improvements in various machine perception tasks such as object detection and recognition. DCNNs are highly non-linear regressors because of the presence of hierarchical convolutional layers with non-linear activation. Unlike the hand crafted features, DCNNs learn the feature extraction and feature classification/regression modules from the data itself in an end-to-end fashion. This enables the DCNNs to be robust to variations present in the data and at the same time improve their discriminative ability. Ever-increasing computation power and availability of large datasets have led to significant performance gains from DCNNs. However, these developments in deep learning are not directly applicable to the face analysis tasks due to large variations in illumination, resolution, viewpoint, and attributes of faces acquired in unconstrained settings. In this dissertation, we address this issue by developing efficient DCNN architectures and loss functions for multiple face analysis tasks such as face detection, pose estimation, landmarks localization, and face recognition from unconstrained images and videos.

In the first part of this dissertation, we present two face detection algorithms based on deep pyramidal features. The first face detector, called DP2MFD, utilizes the concepts of deformable parts model (DPM) in the context of deep learning. It is able to detect faces of various sizes and poses in unconstrained conditions. It reduces the gap in training and testing of DPM on deep features by adding a normalization layer to the DCNN. The second face detector, called Deep Pyramid Single Shot Face Detector (DPSSD), is fast and capable of detecting faces with large scale variations (especially tiny faces). It makes use of the inbuilt pyramidal hierarchy present

in a DCNN, instead of creating an image pyramid. Extensive experiments on publicly available unconstrained face detection datasets show that both these face detectors are able to capture the meaningful structure of faces and perform significantly better than many traditional face detection algorithms.

In the second part of this dissertation, we present two algorithms for simultaneous face detection, landmarks localization, pose estimation and gender recognition using DCNNs. The first method called, HyperFace, fuses the intermediate layers of a DCNN using a separate CNN followed by a multi-task learning algorithm that operates on the fused features. The second approach extends HyperFace to incorporate additional tasks of face verification, age estimation, and smile detection, in All-In-One Face. HyperFace and All-In-One Face exploit the synergy among the tasks which improves individual performances.

In the third part of this dissertation, we focus on improving the task of face verification by designing a novel loss function that maximizes the inter-class distance and minimizes the intraclass distance in the feature space. We propose a new loss function, called Crystal Loss, that adds an L2-constraint to the feature descriptors which restricts them to lie on a hypersphere of a fixed radius. This module can be easily implemented using existing deep learning frameworks. We show that integrating this simple step in the training pipeline significantly boosts the performance of face verification. We additionally describe a deep learning pipeline for unconstrained face identification and verification which achieves state-of-the-art performance on several benchmark datasets. We provide the design details of the various modules involved in automatic face recognition: face detection, landmark localization and alignment, and face identification/verification. We present experimental results for end-to-end face verification and identification on IARPA Janus Benchmarks A, B and C (IJB-A, IJB-B, IJB-C), and the Janus Challenge Set 5 (CS5).

Though DCNNs have surpassed human-level performance on tasks such as object classification and face verification, they can easily be fooled by adversarial attacks. These attacks add a small perturbation to the input image that causes the network to mis-classify the sample. In the final part of this dissertation, we focus on safeguarding the DCNNs and neutralizing adversarial attacks by compact feature learning. In particular, we show that learning features in a closed and bounded space improves the robustness of the network. We explore the effect of Crystal Loss, that enforces compactness in the learned features, thus resulting in enhanced robustness

to adversarial perturbations. Additionally, we propose compact convolution, a novel method of convolution that when incorporated in conventional CNNs improves their robustness. Compact convolution ensures feature compactness at every layer such that they are bounded and close to each other. Extensive experiments show that Compact Convolutional Networks (CCNs) neutralize multiple types of attacks, and perform better than existing methods in defending adversarial attacks, without incurring any additional training overhead compared to CNNs.