In video surveillance, face recognition (FR) systems seek to detect individuals of interest appearing over a distributed network of cameras. Still-to-video FR systems match faces captured in videos under challenging conditions against facial models, often designed using one reference still per individual. Although CNNs can achieve among the highest levels of accuracy in many real-world FR applications, state-of-the-art CNNs that are suitable for still-to-video FR, like trunk-branch ensemble (TBE) CNNs, represent complex solutions for real-time applications. In this paper, an efficient CNN architecture is proposed for accurate still-to-video FR from a single reference still. The CCM-CNN is based on new cross-correlation matching (CCM) and triplet-loss optimization methods that provide discriminant face representations. The matching pipeline exploits a matrix Hadamard product followed by a fully connected layer inspired by adaptive weighted cross-correlation. A triplet-based training approach is proposed to optimize the CCM-CNN parameters such that the inter-class variations are increased, while enhancing robustness to intra-class variations. To further improve robustness, the network is fine-tuned using synthetically-generated faces based on still and videos of non-target individuals. Experiments on videos from the COX Face and Chokepoint datasets indicate that the CCM-CNN can achieve a high level of accuracy that is comparable to TBE-CNN and HaarNet, but with a significantly lower time and memory complexity. It may therefore represent the better trade-off between accuracy and complexity for real-time video surveillance applications.

Video-based face recognition (FR) is a challenging task in real-world applications. In still-to-video FR, probe facial regions of interest (ROIs) are typically captured with lower-quality video cameras under unconstrained conditions, where facial appearances vary according to pose, illumination, scale, expression, etc. These video ROIs are typically compared against facial models designed with high-quality reference still ROI of each target individual enrolled to the system. In this paper, an efficient Canonical Face Representation CNN (CFR-CNN) is proposed for accurate still-to-video FR from a single sample per person, where still and video ROIs are captured in different conditions. Given a facial ROI captured under unconstrained video conditions, the CRF-CNN reconstructs it as a high-quality canonical ROI for matching that corresponds to the conditons of reference still ROIs (e.g., well-illuminated, sharp, frontal views with neutral expression). A deep autoencoder network is trained using a novel weighted loss function that can robustly generate similar face embeddings for the same subjects. Then, during operations, those face embeddings belonging to pairs of still and video ROIs from a target individual are accurately matched using a fully-connected classification network. Experimental results obtained with the COX Face and Chokepoint datasets indicate that the proposed CFR-CNN can achieve convincing level of accuracy. The computational complexity (number of operations, network parameters and layers) is significantly lower than state-of-the-art CNNs for video FR, and suggests that the CFR-CNN represents a cost-effective solution for real-time applications.

Growing number of surveillance and biometric applications seek to recognize the face of individuals appearing in the viewpoint of video cameras. Systems for video-based FR can be subjected to challenging operational environments, where the appearance of faces captured with video cameras varies significantly due to changes in pose, illumination, scale, blur, expression, occlusion, etc. In particular, with still-to-video FR, a limited number of high-quality facial images are typically captured for enrollment of an individual to the system, whereas an abundance facial trajectories can be captured using video cameras during operations, under different viewpoints and uncontrolled conditions. This paper presents a deep learning architecture that can learn a robust facial representation for each target individual during enrollment, and then accurately compare the facial regions of interest (ROIs) extracted from a still reference image (of the target individual) with ROIs extracted from live or archived videos. An ensemble of deep convolutional neural networks (DCNNs) named HaarNet is proposed, where a trunk network first extracts features from the global appearance of the facial ROIs (holistic representation). Then, three branch networks effectively embed asymmetrical and complex facial features (local representations) based on Haar-like features. In order to increase the discriminativness of face representations, a novel regularized triplet-loss function is proposed that reduces the intra-class variations, while increasing the inter-class variations. Given the single reference still per target individual, the robustness of the proposed DCNN is further improved by fine-tuning the HaarNet with synthetically-generated facial still ROIs that emulate capture conditions found in operational environments. The proposed system is evaluated on stills and videos from the challenging COX Face and Chokepoint datasets according to accuracy and complexity. Experimental results indicate that the proposed method can significantly improve performance with respect to state-of-the-art systems for video-based FR.

Recognizing the face of target individuals in a watch-list is among the most challenging applications in video surveillance, especially when enrollment is based on one reference still facial image. Besides the limited representativeness of facial models used for matching, the appearance of faces captured in videos varies due to changes in illumination, pose, scales, etc., and to camera inter-operability. A multi-classifier system is proposed in this paper for robust still-to-video face recognition (FR) based on multiple diverse face representations. An individual-specific ensemble of exemplar-SVMs (e-SVMs) classifiers is assigned to each target person, where each classifier is trained using a high-quality reference face still versus many lower-quality faces of non-target individuals captured in videos. Diverse face representations are generated from different patches isolated in facial images and face descriptors that are robust to various nuisance factors (e.g., illumination and pose) commonly encountered in surveillance environments. Discriminant feature subsets, training samples, and ensemble fusion functions are selected using faces of non-target individuals captured in videos of the scene. Experiments on videos from the Chokepoint dataset reveal that the proposed ensemble of e-SVMs outperforms state-of-the-art FR systems specialized for the single sample per person problem.

Still-to-video face recognition (FR) is an important function in watch list screening, where faces captured over a network of video surveillance cameras are matched against reference stills of target individuals. Recognizing faces in a watch list is a challenging problem in semi -- and unconstrained surveillance environments due to the lack of control over capture and operational conditions, and to the limited number of reference stills. This paper provides a performance baseline and guidelines for ensemble-based systems using a single high-quality reference still per individual, as found in many watch list screening applications. In particular, modular systems are considered, where an ensemble of template matchers based on multiple face representations is assigned to each individual of interest. During enrollment, multiple feature extraction (FE) techniques are applied to patches isolated in the reference still to generate diverse face-part representations that are robust to various nuisance factors (e.g., illumination and pose) encountered in video surveillance. The selection of relevant feature subsets, decision thresholds, and fusion functions of ensembles are achieved using faces of non-target individuals selected from reference videos (forming a universal background model). During operations, a face tracker gradually regroups faces captured from different people appearing in a scene, while each user-specific ensemble generates a decision per face capture. This leads to robust spatio-temporal FR when accumulated ensemble predictions surpass a detection threshold. Simulation results obtained with the Chokepoint video dataset show a significant improvement to accuracy, (1) when performing score-level fusion of matchers, where patches-based and FE techniques generate ensemble diversity, (2) when defining feature subsets and decision thresholds for each individual matcher of an ensemble using non-target videos, and (3) when accumulating positive detections over multiple frames.