@article{choi_wong_su_wu_2023, title={Analysis of ENF Signal Extraction From Videos Acquired by Rolling Shutters}, volume={18}, ISSN={["1556-6021"]}, DOI={10.1109/TIFS.2023.3287132}, abstractNote={Electric network frequency (ENF) analysis is a promising forensic technique for authenticating multimedia recordings and detecting tampering. The validity of the ENF analysis heavily relies on the capability of extracting high-quality ENF signals from multimedia recordings. This paper analyzes and compares two representative methods for extracting ENF signals from visual signals acquired by cameras using the rolling-shutter mechanism. The first method proposed in prior work, direct concatenation, ignores the idle period of each frame. The second method proposed in this paper, periodic zeroing-out, inserts zeros to missing sample points instead of ignoring the idle period. Our theoretical analyses of using multirate signal processing reveal and experiments confirm that while the first method can extract ENF signals without knowing the exact value of camera read-out time, there exists some mild distortion to extracted ENF signals. In contrast, the second method taking the read-out time as the additional input is capable of extracting distortion-free ENF signals, and its frequency component of the highest strength is always located at the nominal frequency. Additionally, we examine aliased DC and negative ENF components caused by the two methods and show that their impact on the accuracy of frequency estimation is minimum. This paper facilitates the fundamental understanding of extracting ENF signals from videos. The research findings imply that the periodic zeroing-out method offers more accurate frequency estimates, but the performance improvement is moderate.}, journal={IEEE TRANSACTIONS ON INFORMATION FORENSICS AND SECURITY}, author={Choi, Jisoo and Wong, Chau-Wai and Su, Hui and Wu, Min}, year={2023}, pages={4229–4242} }
 @article{zhao_wong_2023, title={Automated measures of sentiment via transformer- and lexicon-based sentiment analysis (TLSA)}, volume={11}, ISSN={["2432-2725"]}, DOI={10.1007/s42001-023-00233-8}, journal={JOURNAL OF COMPUTATIONAL SOCIAL SCIENCE}, author={Zhao, Xinyan and Wong, Chau-Wai}, year={2023}, month={Nov} }
 @inproceedings{yue_jin_wong_baron_dai_2023, title={Gradient obfuscation gives a false sense of security in federated learning}, booktitle={USENIX Security Symposium 2023}, author={Yue, Kai and Jin, Richeng and Wong, Chau-Wai and Baron, Dror and Dai, Huaiyu}, year={2023}, month={Aug} }
 @article{cao_goenka_wong_rajwade_baron_2023, title={Group Testing With Side Information via Generalized Approximate Message Passing}, volume={71}, ISSN={["1941-0476"]}, url={https://doi.org/10.1109/TSP.2023.3287671}, DOI={10.1109/TSP.2023.3287671}, abstractNote={Group testing can help maintain a widespread testing program using fewer resources amid a pandemic. In a group testing setup, we are given <inline-formula><tex-math notation="LaTeX">$n$</tex-math></inline-formula> samples, one per individual. Each individual is either infected or uninfected. These samples are arranged into <inline-formula><tex-math notation="LaTeX">$m < n$</tex-math></inline-formula> pooled samples, where each pool is obtained by mixing a subset of the <inline-formula><tex-math notation="LaTeX">$n$</tex-math></inline-formula> individual samples. Infected individuals are then identified using a group testing algorithm. In this article, we incorporate side information (SI) collected from contact tracing (CT) into nonadaptive/single-stage group testing algorithms. We generate different types of CT SI data by incorporating different possible characteristics of the spread of disease. These data are fed into a group testing framework based on generalized approximate message passing (GAMP). Numerical results show that our GAMP-based algorithms provide improved accuracy.}, journal={IEEE TRANSACTIONS ON SIGNAL PROCESSING}, author={Cao, Shu-Jie and Goenka, Ritesh and Wong, Chau-Wai and Rajwade, Ajit and Baron, Dror}, year={2023}, pages={2366–2375} }
 @article{mathew_tian_wong_ho_milton_wu_2023, title={Remote Blood Oxygen Estimation From Videos Using Neural Networks}, volume={27}, ISSN={["2168-2208"]}, DOI={10.1109/JBHI.2023.3236631}, abstractNote={Peripheral blood oxygen saturation (SpO<inline-formula><tex-math notation="LaTeX">$_{2}$</tex-math></inline-formula>) is an essential indicator of respiratory functionality and received increasing attention during the COVID-19 pandemic. Clinical findings show that COVID-19 patients can have significantly low SpO<inline-formula><tex-math notation="LaTeX">$_{2}$</tex-math></inline-formula> before any obvious symptoms. Measuring an individual's SpO<inline-formula><tex-math notation="LaTeX">$_{2}$</tex-math></inline-formula> without having to come into contact with the person can lower the risk of cross contamination and blood circulation problems. The prevalence of smartphones has motivated researchers to investigate methods for monitoring SpO<inline-formula><tex-math notation="LaTeX">$_{2}$</tex-math></inline-formula> using smartphone cameras. Most prior schemes involving smartphones are contact-based: They require using a fingertip to cover the phone's camera and the nearby light source to capture reemitted light from the illuminated tissue. In this paper, we propose the first convolutional neural network based noncontact SpO<inline-formula><tex-math notation="LaTeX">$_{2}$</tex-math></inline-formula> estimation scheme using smartphone cameras. The scheme analyzes the videos of an individual's hand for physiological sensing, which is convenient and comfortable for users and can protect their privacy and allow for keeping face masks on. We design explainable neural network architectures inspired by the optophysiological models for SpO<inline-formula><tex-math notation="LaTeX">$_{2}$</tex-math></inline-formula> measurement and demonstrate the explainability by visualizing the weights for channel combination. Our proposed models outperform the state-of-the-art model that is designed for contact-based SpO<inline-formula><tex-math notation="LaTeX">$_{2}$</tex-math></inline-formula> measurement, showing the potential of the proposed method to contribute to public health. We also analyze the impact of skin type and the side of a hand on SpO<inline-formula><tex-math notation="LaTeX">$_{2}$</tex-math></inline-formula> estimation performance.}, number={8}, journal={IEEE JOURNAL OF BIOMEDICAL AND HEALTH INFORMATICS}, author={Mathew, Joshua and Tian, Xin and Wong, Chau-Wai and Ho, Simon and Milton, Donald K. and Wu, Min}, year={2023}, month={Aug}, pages={3710–3720} }
 @article{kashyap_ravichandiran_wang_baron_wong_wu_franzon_2023, title={Thermal Estimation for 3D-ICs through Generative Networks}, ISSN={["2164-0157"]}, DOI={10.1109/3DIC57175.2023.10154977}, abstractNote={Thermal limitations play a significant role in modern integrated chips (ICs) design and performance. 3D integrated chip (3DIC) makes the thermal problem even worse due to a high density of transistors and heat dissipation bottlenecks within the stack-up. These issues exacerbate the need for quick thermal solutions throughout the design flow. This paper presents a generative approach for modeling the power to heat dissipation for a 3DIC. This approach focuses on a single layer in a stack and shows that, given the power map, the model can generate the resultant heat for the bulk. It shows two approaches, one straightforward approach where the model only uses the power map and the other where it learns the additional parameters through random vectors. The first approach recovers the temperature maps with 1.2 C° or a root-mean-squared error (RMSE) of 0.31 over the images with pixel values ranging from -1 to 1. The second approach performs better, with the RMSE decreasing to 0.082 in a 0 to 1 range. For any result, the model inference takes less than 100 millisecond for any given power map. These results show that the generative approach has speed advantages over traditional solvers while enabling results with reasonable accuracy for 3DIC, opening the door for thermally aware floorplanning.}, journal={2023 IEEE INTERNATIONAL 3D SYSTEMS INTEGRATION CONFERENCE, 3DIC}, author={Kashyap, Priyank and Ravichandiran, Prasanth P. and Wang, Lee and Baron, Dror and Wong, Chau-Wai and Wu, Tianfu and Franzon, Paul D.}, year={2023} }
 @article{tian_wong_ranadive_wu_2022, title={A Multi-Channel Ratio-of-Ratios Method for Noncontact Hand Video Based SpO(2) Monitoring Using Smartphone Cameras}, volume={16}, ISSN={["1941-0484"]}, DOI={10.1109/JSTSP.2022.3152352}, abstractNote={Blood oxygen saturation (SpO<inline-formula><tex-math notation="LaTeX">$_2$</tex-math></inline-formula>) is an important indicator forpulmonary and respiratory functionalities. Clinical findings on COVID-19 show that many patients had dangerously low blood oxygen levels not long before conditions worsened. It is therefore recommended, especially for the vulnerable population, to regularly monitor the blood oxygen level for precaution. Recent works have investigated how ubiquitous smartphone cameras can be used to infer SpO<inline-formula><tex-math notation="LaTeX">$_2$</tex-math></inline-formula>. Most of these works are contact-based, requiring users to cover a phone’s camera and its nearby light source with a finger to capture reemitted light from the illuminated tissue. Contact-based methods may lead to skin irritation and sanitary concerns, especially during a pandemic. In this paper, we propose a noncontact method for SpO<inline-formula><tex-math notation="LaTeX">$_2$</tex-math></inline-formula> monitoring using hand videos acquired by smartphones. Considering the optical broadband nature of the red (R), green (G), and blue (B) color channels of the smartphone cameras, we exploit all three channels of RGB sensing to distill the SpO<inline-formula><tex-math notation="LaTeX">$_2$</tex-math></inline-formula> information beyond the traditional ratio-of-ratios (RoR) method that uses only two wavelengths. To further facilitate an accurate SpO<inline-formula><tex-math notation="LaTeX">$_2$</tex-math></inline-formula> prediction, we design adaptive narrow bandpass filters based on accurately estimated heart rate to obtain the most cardiac-related AC component for each color channel. Experimental results show that our proposed blood oxygen estimation method can reach a mean absolute error of 1.26% when a pulse oximeter is used as a reference, outperforming the traditional RoR method by 25%.}, number={2}, journal={IEEE JOURNAL OF SELECTED TOPICS IN SIGNAL PROCESSING}, author={Tian, Xin and Wong, Chau-Wai and Ranadive, Sushant M. and Wu, Min}, year={2022}, month={Feb}, pages={197–207} }
 @article{yue_jin_wong_dai_2022, title={Communication-Efficient Federated Learning via Predictive Coding}, volume={16}, ISSN={["1941-0484"]}, DOI={10.1109/JSTSP.2022.3142678}, abstractNote={Federated learning can enable remote workers to collaboratively train a shared machine learning model while allowing training data to be kept locally. In the use case of wireless mobile devices, the communication overhead is a critical bottleneck due to limited power and bandwidth. Prior work has utilized various data compression tools such as quantization and sparsification to reduce the overhead. In this paper, we propose a predictive coding based compression scheme for federated learning. The scheme has shared prediction functions among all devices and allows each worker to transmit a compressed residual vector derived from the reference. In each communication round, we select the predictor and quantizer based on the rate–distortion cost, and further reduce the redundancy with entropy coding. Extensive simulations reveal that the communication cost can be reduced up to 99% with even better learning performance when compared with other baseline methods.}, number={3}, journal={IEEE JOURNAL OF SELECTED TOPICS IN SIGNAL PROCESSING}, author={Yue, Kai and Jin, Richeng and Wong, Chau-Wai and Dai, Huaiyu}, year={2022}, month={Apr}, pages={369–380} }
 @article{holder_rahman_summers_roberts_wong_bozkurt_2022, title={Contact-Free Simultaneous Sensing of Human Heart Rate and Canine Breathing Rate for Animal Assisted Interactions}, DOI={10.1145/3565995.3566039}, abstractNote={Animal Assisted Interventions (AAIs) involve pleasant interactions between humans and animals and can potentially benefit both types of participants. Research in this field may help to uncover universal insights about cross-species bonding, dynamic affect detection, and the influence of environmental factors on dyadic interactions. However, experiments evaluating these outcomes are limited to methodologies that are qualitative, subjective, and cumbersome due to the ergonomic challenges related to attaching sensors to the body. Current approaches in AAIs also face challenges when translating beyond controlled clinical environments or research contexts. These also often neglect the measurements from the animal throughout the interaction. Here, we present our preliminary effort toward a contact-free approach to facilitate AAI assessment via the physiological sensing of humans and canines using consumer-grade cameras. This initial effort focuses on verifying the technological feasibility of remotely sensing the heart rate signal of the human subject and the breathing rate signal of the dog subject while they are interacting. Small amounts of motion such as patting and involuntary body shaking or movement can be tolerated with our custom designed vision-based algorithms. The experimental results show that the physiological measurements obtained by our algorithms were consistent with those provided by the standard reference devices. With further validation and expansion to other physiological parameters, the presented approach offers great promise for many scenarios from the AAI research space to veterinary, surgical, and clinical applications.}, journal={NINTH INTERNATIONAL CONFERENCE ON ANIMAL-COMPUTER INTERACTION, ACI 2022}, author={Holder, Timothy and Rahman, Mushfiqur and Summers, Emily and Roberts, David and Wong, Chau-Wai and Bozkurt, Alper}, year={2022} }
 @article{yue_jin_wong_dai_2022, title={Federated Learning via Plurality Vote}, volume={12}, ISSN={["2162-2388"]}, DOI={10.1109/TNNLS.2022.3225715}, abstractNote={Federated learning allows collaborative clients to solve a machine-learning problem while preserving data privacy. Recent studies have tackled various challenges in federated learning, but the joint optimization of communication overhead, learning reliability, and deployment efficiency is still an open problem. To this end, we propose a new scheme named federated learning via plurality vote (FedVote). In each communication round of FedVote, clients transmit binary or ternary weights to the server with low communication overhead. The model parameters are aggregated via weighted voting to enhance the resilience against Byzantine attacks. When deployed for inference, the model with binary or ternary weights is resource-friendly to edge devices. Our results demonstrate that the proposed method can reduce quantization error and converges faster compared to the methods directly quantizing the model updates.}, journal={IEEE TRANSACTIONS ON NEURAL NETWORKS AND LEARNING SYSTEMS}, author={Yue, Kai and Jin, Richeng and Wong, Chau-Wai and Dai, Huaiyu}, year={2022}, month={Dec} }
 @article{choi_wong_hajj-alunado_wa_ren_2022, title={Invisible Geolocation Signature Extraction From a Single Image}, volume={17}, ISSN={["1556-6021"]}, DOI={10.1109/TIFS.2022.3185775}, abstractNote={Geotagging images of interest are increasingly important to law enforcement, national security, and journalism. Today, many images do not carry location tags that are trustworthy and resilient to tampering; and landmark-based visual clues may not be readily present in every image, especially in those taken indoors. In this paper, we exploit an environmental signature from the power grid, the electric network frequency (ENF) signal, which can be inherently captured in a sensing stream at the time of recording and carries useful time&#x2013;location information. Compared to the recent art of extracting ENF traces from audio and video recordings, it is very challenging to extract an ENF trace from a single image. We address this challenge by first mathematically examining the impact of the ENF embedding steps such as electricity to light conversion, scene geometry dilution of radiation, and image sensing. We then incorporate the verified parametric models of the physical embedding process into our proposed entropy minimization method. The optimized results of the entropy minimization are used for creating a two-level ENF presence&#x2013;classification test for region-of-capturing localization. It identifies whether a single image has an ENF trace; if yes, whether it is at 50 or 60 Hz. We quantitatively study the relationship between the ENF strength and its detectability from a single image. This paper is the first comprehensive work to bring out a unique forensic capability of environmental traces that shed light on an image&#x2019;s capturing location.}, journal={IEEE TRANSACTIONS ON INFORMATION FORENSICS AND SECURITY}, author={Choi, Jisoo and Wong, Chau-Wai and Hajj-AlunadO, Adi and Wa, Min and Ren, Yanpin}, year={2022}, month={Jun}, pages={2598–2613} }
 @article{abdelkhalek_baron_wong_2022, title={Mismatched Estimation in the Distance Geometry Problem}, ISSN={["1058-6393"]}, DOI={10.1109/IEEECONF56349.2022.10051876}, abstractNote={We investigate mismatched estimation in the context of the distance geometry problem (DGP). In the DGP, for a set of points, we are given noisy measurements of pairwise distances between the points, and our objective is to determine the geometric locations of the points. A common approach to deal with noisy measurements of pairwise distances is to compute least-squares estimates of the locations of the points. However, these least-squares estimates are likely to be suboptimal, because they do not necessarily maximize the correct likelihood function. In this paper, we argue that more accurate estimates can be obtained when an estimation procedure that uses the correct likelihood function of noisy measurements is performed. Our numerical results demonstrate that least-squares estimates can be suboptimal by several dB.}, journal={2022 56TH ASILOMAR CONFERENCE ON SIGNALS, SYSTEMS, AND COMPUTERS}, author={Abdelkhalek, Mahmoud and Baron, Dror and Wong, Chau-Wai}, year={2022}, pages={1031–1035} }
 @article{kashyap_choi_dey_baron_wong_wu_cheng_franzon_2022, title={Modeling of Adaptive Receiver Performance Using Generative Adversarial Networks}, ISSN={["2377-5726"]}, url={http://dx.doi.org/10.1109/ectc51906.2022.00307}, DOI={10.1109/ECTC51906.2022.00307}, abstractNote={As the development of IBIS Algorithmic Modeling Interface (IBIS-AMI) models gets complex and requires time-consuming simulations, a data-driven and domain-independent approach can have tremendous value. This paper presents a data-driven approach to modeling a high-speed serializer/deserializer (SerDes) receiver through generative adversarial networks (GANs). In this work, the modeling considers multiple channels, random bitstreams, and varying decision feedback equalizer (DFE) tap values to predict an accurate bit error rate (BER) contour plot. We employ a discriminator structure that improves the training to generate a contour plot that makes it difficult to distinguish the ground truth. The generated plots’ bathtub curves strongly correlate to the ground truth bathtub curves and have a root-mean-squared error (RMSE) of 0.014, indicating a good fit.}, journal={IEEE 72ND ELECTRONIC COMPONENTS AND TECHNOLOGY CONFERENCE (ECTC 2022)}, publisher={IEEE}, author={Kashyap, Priyank and Choi, Yongjin and Dey, Sumon and Baron, Dror and Wong, Chau-Wai and Wu, Tianfu and Cheng, Chris and Franzon, Paul D.}, year={2022}, pages={1958–1963} }
 @inproceedings{neural tangent kernel empowered federated learning_2022, booktitle={International Conference on Machine Learning (ICML)}, year={2022}, month={Jul} }
 @article{kashyap_gajjar_choi_wong_baron_wu_cheng_franzon_2022, title={RxGAN: Modeling High-Speed Receiver through Generative Adversarial Networks}, url={http://dx.doi.org/10.1145/3551901.3556480}, DOI={10.1145/3551901.3556480}, abstractNote={Creating models for modern high-speed receivers using circuit-level simulations is costly, as it requires computationally expensive simulations and upwards of months to finalize a model. Added to this is that many models do not necessarily agree with the final hardware they are supposed to emulate. Further, these models are complex due to the presence of various filters, such as a decision feedback equalizer (DFE) and continuous-time linear equalizer (CTLE), which enable the correct operation of the receiver. Other data-driven approaches tackle receiver modeling through multiple models to account for as many configurations as possible. This work proposes a data-driven approach using generative adversarial training to model a real-world receiver with varying DFE and CTLE configurations while handling different channel conditions and bitstreams. The approach is highly accurate as the eye height and width are within 1.59% and 1.12% of the ground truth. The horizontal and vertical bathtub curves match the ground truth and correlate to the ground truth bathtub curves.}, journal={MLCAD '22: PROCEEDINGS OF THE 2022 ACM/IEEE 4TH WORKSHOP ON MACHINE LEARNING FOR CAD (MLCAD)}, publisher={ACM}, author={Kashyap, Priyank and Gajjar, Archit and Choi, Yongjin and Wong, Chau-Wai and Baron, Dror and Wu, Tianfu and Cheng, Chris and Franzon, Paul}, year={2022}, pages={167–172} }
 @article{goenka_cao_wong_rajwade_baron_2021, title={CONTACT TRACING ENHANCES THE EFFICIENCY OF COVID-19 GROUP TESTING}, DOI={10.1109/ICASSP39728.2021.9414034}, abstractNote={Group testing can save testing resources in the context of the ongoing COVID-19 pandemic. In group testing, we are given n samples, one per individual, and arrange them into m < n pooled samples, where each pool is obtained by mixing a subset of the n individual samples. Infected individuals are then identified using a group testing algorithm. In this paper, we use side information (SI) collected from contact tracing (CT) within nonadaptive/single-stage group testing algorithms. We generate data by incorporating CT SI and characteristics of disease spread between individuals. These data are fed into two signal and measurement models for group testing, where numerical results show that our algorithms provide improved sensitivity and specificity. While Nikolopoulos et al. utilized family structure to improve nonadaptive group testing, ours is the first work to explore and demonstrate how CT SI can further improve group testing performance.}, journal={2021 IEEE INTERNATIONAL CONFERENCE ON ACOUSTICS, SPEECH AND SIGNAL PROCESSING (ICASSP 2021)}, author={Goenka, Ritesh and Cao, Shu-Jie and Wong, Chau-Wai and Rajwade, Ajit and Baron, Dror}, year={2021}, pages={8168–8172} }
 @article{kashyap_pitts_baron_wong_wu_franzon_2021, title={High Speed Receiver Modeling Using Generative Adversarial Networks}, ISSN={["2165-4107"]}, DOI={10.1109/EPEPS51341.2021.9609124}, abstractNote={This paper presents a generative approach to modeling a high-speed receiver with a time series input. The model is not built with domain knowledge but learned from a wide range of channel conditions and input bitstreams to generate an eye diagram. The generated eye diagrams are similar to the simulated eye diagrams for the same scenario. We also developed a neural network model to evaluate the generated eye diagram's relevant characteristics, such as eye height and width. The generated eye diagrams are within 7% and 3% error to the ground-truth in eye height and eye width, respectively, based on our evaluation neural network.}, journal={IEEE 30TH CONFERENCE ON ELECTRICAL PERFORMANCE OF ELECTRONIC PACKAGING AND SYSTEMS (EPEPS 2021)}, author={Kashyap, Priyank and Pitts, W. Shepherd and Baron, Dror and Wong, Chau-Wai and Wu, Tianfu and Franzon, Paul D.}, year={2021} }
 @article{zhu_tian_wong_wu_2021, title={Learning Your Heart Actions From Pulse: ECG Waveform Reconstruction From PPG}, volume={8}, ISSN={["2327-4662"]}, DOI={10.1109/JIOT.2021.3097946}, abstractNote={This article studies the relation between electrocardiogram (ECG) and photoplethysmogram (PPG) and investigates the inference of the ECG waveforms from the PPG signals that can be obtained from affordable wearable Internet-of-Things (IoT) devices for mobile health. In order to address this inverse problem, a transform is proposed to map the discrete cosine transform (DCT) coefficients of each PPG cycle to those of the corresponding ECG cycle based on the proposed cardiovascular signal model. The proposed method is evaluated with different morphologies of the PPG and ECG signals on three benchmark data sets with a variety of combinations of age, weight, and health conditions under several training setups. The experimental results show that the proposed method can achieve a high prediction accuracy greater than 0.92 in averaged correlation for each data set when the model is trained subjectwise. With a signal processing and learning system that is designed synergistically, we are able to reconstruct ECG signals by exploiting the relation of these two types of cardiovascular measurement. The reconstruction capability of the proposed method can enable low-cost ECG screening from affordable wearable IoT devices for continuous and long-term monitoring. This work opens up a new research direction to transfer the clinical ECG knowledge base to build a knowledge base for PPG and sensing data from wearable devices.}, number={23}, journal={IEEE INTERNET OF THINGS JOURNAL}, author={Zhu, Qiang and Tian, Xin and Wong, Chau-Wai and Wu, Min}, year={2021}, month={Dec}, pages={16734–16748} }
 @article{liu_wong_2021, title={On Microstructure Estimation Using Flatbed Scanners for Paper Surface-Based Authentication}, volume={16}, ISSN={["1556-6021"]}, url={http://dx.doi.org/10.1109/tifs.2021.3071585}, DOI={10.1109/TIFS.2021.3071585}, abstractNote={Paper surfaces under the microscopic view are observed to be formed by intertwisted wood fibers. Such structures of paper surfaces are unique from one location to another and are almost impossible to duplicate. Previous work used microscopic surface normals to characterize such intrinsic structures as a “fingerprint” of paper for security and forensic applications. In this work, we examine several key research questions of feature extraction in both scientific and engineering aspects to facilitate the deployment of paper surface-based authentication when flatbed scanners are used as the acquisition device. We analytically show that, under the unique optical setup of flatbed scanners, the specular reflection does not play a role in norm map estimation. We verify, using a larger dataset than prior work, that the scanner-acquired norm maps, although blurred, are consistent with those measured by confocal microscopes. We confirm that, when choosing an authentication feature, high spatial-frequency subbands of the heightmap are more powerful than the norm map. Finally, we show that it is possible to empirically calculate the physical dimensions of the paper patch needed to achieve a certain authentication performance in equal error rate (EER). We analytically show that log(EER) is decreasing linearly in the edge length of a paper patch.}, journal={IEEE TRANSACTIONS ON INFORMATION FORENSICS AND SECURITY}, publisher={Institute of Electrical and Electronics Engineers (IEEE)}, author={Liu, Runze and Wong, Chau-Wai}, year={2021}, pages={3039–3053} }
 @inproceedings{wu_wong_zhao_liu_2021, title={Toward Effective Automated Content Analysis via Crowdsourcing}, url={http://dx.doi.org/10.1109/icme51207.2021.9428220}, DOI={10.1109/icme51207.2021.9428220}, abstractNote={Many computer scientists use the aggregated answers of online workers to represent ground truth. Prior work has shown that aggregation methods such as majority voting are effective for measuring relatively objective features. For subjective features such as semantic connotation, online workers, known for optimizing their hourly earnings, tend to deteriorate in the quality of their responses as they work longer. In this paper, we aim to address this issue by proposing a quality-aware semantic data annotation system. We observe that with timely feedback on workers’ performance quantified by quality scores, better informed online workers can maintain the quality of their labeling throughout an extended period of time. We validate the effectiveness of the proposed annotation system through i) evaluating performance based on an expert-labeled dataset, and ii) demonstrating machine learning tasks that can lead to consistent learning behavior with 70%–80% accuracy. Our results suggest that with our system, researchers can collect high-quality answers of subjective semantic features at a large scale.}, booktitle={IEEE International Conference on Multimedia and Expo (ICME)}, publisher={IEEE}, author={Wu, Jiele and Wong, Chau-Wai and Zhao, Xinyan and Liu, Xianpeng}, year={2021}, month={Jul} }
 @article{zhu_chen_wong_wu_2020, title={Adaptive Multi-Trace Carving for Robust Frequency Tracking in Forensic Applications}, url={http://dx.doi.org/10.1109/tifs.2020.3030182}, DOI={10.1109/tifs.2020.3030182}, abstractNote={In the field of information forensics, many emerging problems involve a critical step that estimates and tracks weak frequency components in noisy signals. It is often challenging for the prior art of frequency tracking to i) achieve a high accuracy under noisy conditions, ii) detect and track multiple frequency components efficiently, or iii) strike a good trade-off of the processing delay versus the resilience and the accuracy of tracking. To address these issues, we propose Adaptive Multi-Trace Carving (AMTC), a unified approach for detecting and tracking one or more subtle frequency components under very low signal-to-noise ratio (SNR) conditions and in near real time. AMTC takes as input a time-frequency representation of the system’s preprocessing results (such as the spectrogram), and identifies frequency components through iterative dynamic programming and adaptive trace compensation. The proposed algorithm considers relatively high energy traces sustaining over a certain duration as an indicator of the presence of frequency/oscillation components of interest and track their time-varying trend. Extensive experiments using both synthetic data and real-world forensic data of power signatures and physiological monitoring reveal that the proposed method outperforms representative prior art under low SNR conditions, and can be implemented in near real-time settings. The proposed AMTC algorithm can empower the development of new information forensic technologies that harness very small signals.}, journal={IEEE Transactions on Information Forensics and Security}, publisher={Institute of Electrical and Electronics Engineers (IEEE)}, author={Zhu, Qiang and Chen, Mingliang and Wong, Chau-Wai and Wu, Min}, year={2020} }
 @article{lai_claffey_chen_zhang_wu_chau-wai_wang_au_liu_2020, title={Method, apparatus, and system for object tracking sensing using broadcasting}, note={US Patent 10,742,475}, author={Lai, Hung-quoc Duc and Claffey, David N and Chen, Chen and Zhang, Feng and Wu, Chenshu and Chau-Wai, WONG and Wang, Beibei and Au, Oscar Chi-lim and Liu, KJ Ray}, year={2020}, month={Aug} }
 @article{liu_wong_2020, title={On Microstructure Estimation Using Flatbed Scanners for Paper Surface Based Authentication}, journal={arXiv preprint arXiv:2008.13000}, author={Liu, Runze and Wong, Chau-Wai}, year={2020} }
 @article{zhao_yang_wong_2019, title={Analyzing Trend for US Immigrants' e-Health Engagement from 2008 to 2013}, volume={34}, ISSN={["1532-7027"]}, DOI={10.1080/10410236.2018.1475999}, abstractNote={ABSTRACT Our study examines the trend of U.S. immigrants’ engagement in various e-health activities and how immigrants’ use of e-health technologies is associated with their cultural characteristics over years. Aggregating three national representative samples of U.S. immigrants from the Health Information National Trends Survey (HINTS) conducted between 2008 and 2013, our results from trend analyses and logistic regressions revealed that the U.S. immigrants exhibited an increasing trend on two types of e-health engagement: tracking personal health information online and communicating with a doctor online. But we did not find any significant change in the other two e-health activities throughout these years: the percentage of immigrants who sought a health provider online remained moderate (about 37%), whereas the percentage of immigrants who joined an online support group kept low (about 5%). Furthermore, immigrants of different race/ethnicity or length of residence in the United States showed different trends of e-health engagement. Asian immigrants and immigrants with 13–34 years of residence were more proactive to engage in various e-health activities. Our study informs the practice aiming to enhance U.S. immigrants’ Internet use for better health-related outcomes.}, number={11}, journal={HEALTH COMMUNICATION}, author={Zhao, Xinyan and Yang, Bo and Wong, Chau-Wai}, year={2019}, month={Sep}, pages={1259–1269} }
 @article{xu_zhang_chen_wang_wu_zhang_chau-wai_claffey_chen_lai_et al._2019, title={Apparatus, systems and methods for event recognition based on a wireless signal}, note={US Patent 10,374,863}, publisher={Google Patents}, author={Xu, Qinyi and Zhang, Feng and Chen, Chen and Wang, Beibei and Wu, Chenshu and Zhang, Hangfang and Chau-Wai, WONG and Claffey, David N and Chen, Chun-I and Lai, Hung-Quoc Duc and et al.}, year={2019}, month={Aug} }
 @article{zhang_chen_xu_wang_wu_zhang_chau-wai_claffey_chen_lai_et al._2019, title={Apparatus, systems and methods for fall-down detection based on a wireless signal}, note={US Patent 10,397,039}, publisher={Google Patents}, author={Zhang, Feng and Chen, Chen and Xu, Qinyi and Wang, Beibei and Wu, Chenshu and Zhang, Hangfang and Chau-Wai, WONG and Claffey, David N and Chen, Chun-I and Lai, Hung-Quoc Duc and et al.}, year={2019}, month={Aug} }
 @inproceedings{zhu_tian_wong_wu_2019, title={ECG reconstruction via PPG: A pilot study}, DOI={10.1109/BHI.2019.8834612}, abstractNote={In this paper, the relation between electrocardiogram (ECG) and photoplethysmogram (PPG) signals is studied, and the waveform of ECG is inferred via the PPG signals. In order to address this inverse problem, a transform is proposed to map the discrete cosine transform (DCT) coefficients of each PPG cycle to those of the corresponding ECG cycle. The resulting DCT coefficients of the ECG cycle are inversely transformed to obtain the reconstructed ECG waveform. The proposed method is evaluated on a benchmark dataset of subjects with a variety of combinations of age and weight. Experimental results show that the proposed method can achieve a high accuracy at 0.98 in averaged correlation.}, booktitle={IEEE/EMBS International Conference on Biomedical & Health Informatics (BHI)}, author={Zhu, Qiang and Tian, Xin and Wong, Chau-Wai and Wu, Min}, year={2019} }
 @inproceedings{choi_wong_2019, title={ENF Signal Extraction for Rolling-shutter Videos Using Periodic Zero-Padding}, booktitle={IEEE International Conference on Acoustics, Speech and Signal Processing (ICASSP)}, author={Choi, Jisoo and Wong, Chau-Wai}, year={2019}, pages={2667–2671} }
 @article{wong_2019, title={Efficient Video Data Structure and Compression Scheme for Fabric Wicking Phenomenon Studies}, DOI={10.1109/MIPR.2019.00084}, abstractNote={The physiological comfortableness of clothes is heavily attributed to the wicking phenomenon of fabrics. We have been working with textile scientists to automate a newly designed video-based test method that targets at analyzing the yarn-level wicking behaviors of fabrics. To access yarn-level wicking information, we need an efficient video data structure that allows the retrieval of the color information at each pixel along the time. In this paper, we propose using the volume of blocks as the basic storage unit rather than using the frame as most off-the-shelf video codecs do. The proposed data structure allows quick retrieval of time series data and can achieve a balance between the time overhead and memory overhead. We also propose a compression scheme specially designed for the proposed data structure. Experimental results show that the proposed data structure and compression scheme can store the video information in manageable file size while providing visual quality at a customized level.}, journal={2019 2ND IEEE CONFERENCE ON MULTIMEDIA INFORMATION PROCESSING AND RETRIEVAL (MIPR 2019)}, author={Wong, Chau-Wai}, year={2019}, pages={415–418} }
 @article{hajj-ahmad_wong_gambino_zhu_yu_wu_2019, title={Factors Affecting ENF Capture in Audio}, volume={14}, ISSN={["1556-6021"]}, DOI={10.1109/TIFS.2018.2837645}, abstractNote={The electric network frequency (ENF) signal is an environmental signature that can be captured in audiovisual recordings made in locations where there is electrical activity. This signal is influenced by the power grid in which the recording is made, and recent work has shown that it can be useful toward a number of forensics and security applications. An under-studied area of ENF research is the factors that can affect the capture of ENF traces in media recordings. Not all recordings made in the areas of electrical activity will carry prominent ENF traces, and the strengths by which the ENF traces are captured can vary from one recording to another. A thorough understanding of the factors that can affect the capture of ENF traces in recordings is essential to understanding the applicability of ENF-based approaches and can help inform related studies in the future. This paper carried out a study on such factors, with a focus on audio signals. The impact of the characteristics of an audio recorder and the environment and manner of recording on the intrinsically captured ENF are shown and analyzed.}, number={2}, journal={IEEE TRANSACTIONS ON INFORMATION FORENSICS AND SECURITY}, publisher={IEEE}, author={Hajj-Ahmad, Adi and Wong, Chau-Wai and Gambino, Steven and Zhu, Qiang and Yu, Miao and Wu, Min}, year={2019}, month={Feb}, pages={277–288} }
 @article{zhu_tian_wong_wu_2019, title={Learning Your Heart Actions From Pulse: ECG Waveform Reconstruction From PPG}, volume={10}, url={http://dx.doi.org/10.1101/815258}, DOI={10.1101/815258}, abstractNote={Abstract}, journal={bioRxiv}, publisher={Cold Spring Harbor Laboratory}, author={Zhu, Qiang and Tian, Xin and Wong, Chau-Wai and Wu, Min}, year={2019}, month={Oct}, pages={815258} }
 @article{zhang_lai_chen_chau-wai_wang_chen_au_han_liu_2019, title={Method, apparatus, and system for object tracking and navigation}, note={US Patent 10,270,642}, publisher={Google Patents}, author={Zhang, Feng and Lai, Hung-Quoc Duc and Chen, Chun-I and Chau-Wai, WONG and Wang, Beibei and Chen, Chen and Au, Oscar Chi-Lim and Han, Yi and Liu, KJ Ray}, year={2019}, month={Apr} }
 @article{zhang_chen_xu_wang_wu_zhang_chau-wai_claffey_chen_lai_et al._2019, title={Method, apparatus, server and system for real-time vital sign detection and monitoring}, note={US Patent 10,495,725}, publisher={Google Patents}, author={Zhang, Feng and Chen, Chen and Xu, Qinyi and Wang, Beibei and Wu, Chenshu and Zhang, Hangfang and Chau-Wai, WONG and Claffey, David N and Chen, Chun-I and Lai, Hung-Quoc Duc and et al.}, year={2019}, month={Dec} }
 @article{chen_zhang_xu_wang_wu_zhang_wong_claffey_chen_lai_et al._2019, title={Method, apparatus, server and system for vital sign detection and monitoring}, note={US Patent App. 16/200,608}, author={Chen, Chen and Zhang, Feng and Xu, Qinyi and Wang, Beibei and Wu, Chenshu and Zhang, Hangfang and Wong, Chau-Wai and Claffey, David N and Chen, Chun-i and Lai, Hung-quoc Duc and et al.}, year={2019}, month={May} }
 @inproceedings{liu_wong_2019, title={Video-Based Wetting Detection For Blended Fabrics}, url={http://dx.doi.org/10.1109/ieeeconf44664.2019.9048999}, DOI={10.1109/ieeeconf44664.2019.9048999}, abstractNote={Textile scientists are seeking for automated ways to understand the wicking phenomenon of blended fabrics from recorded videos at the pixel level. In response to such need, we design a video-based method for detecting pixels that will become wet and for estimating the timestamps of wetting events, which is the first step toward characterizing the wicking phenomenon. Since the wicking behaviors of the blended fabrics can be very different from one yarn to another within a small spatial region, simple frame-level thresholding with morphological preprocessing steps does not fit this application scenario. In this paper, we analyze for each pixel the color variation along the time for the wetting event detection. We develop an iterative merging algorithm rooted from the likelihood ratio test to obtain a coarse-level timestamp. The timestamp is then refined using a parametric curve fitted to a small neighborhood. Experimental results show that our automated method can achieve satisfactory wetting detection performance when the generated binary wetting-event video is compared with the raw wicking video.}, booktitle={53rd Asilomar Conference on Signals, Systems, and Computers}, publisher={IEEE}, author={Liu, Xianpeng and Wong, Chau-Wai}, year={2019}, month={Nov} }
 @inproceedings{zhu_chen_wong_wu_2018, title={Adaptive multi-trace carving based on dynamic programming}, DOI={10.1109/ACSSC.2018.8645216}, abstractNote={In this paper, we study the problem of tracking multiple frequency components in a noisy signal using a spectrogram-based method. Previous approaches such as image processing based or hidden Markov model based methods may not be capable of tracking multiple frequency components, may require extensive training, and may be time-consuming. To address these issues, we propose an accurate and efficient method named Adaptive Multi-Trace Carving (AMTC) for tracking multiple frequency traces by iterative forward and backward dynamic programming and adaptive trace compensation. Experimental results reveal that the proposed method outperforms the state-of-the-art methods especially under low SNR conditions.}, booktitle={52nd Asilomar Conference on Signals, Systems, and Computers}, author={Zhu, Qiang and Chen, Mingliang and Wong, Chau-Wai and Wu, Min}, year={2018}, pages={1716–1720} }
 @article{zhao_yang_wong_2018, title={Analyzing trend for US immigrants’ e-Health engagement from 2008 to 2013}, journal={Health communication}, publisher={Routledge}, author={Zhao, Xinyan and Yang, Bo and Wong, Chau-Wai}, year={2018} }
 @article{wu_wong_2018, title={Counterfeit detection scheme using paper surfaces and mobile cameras}, note={US Patent App. 15/775,977}, author={Wu, Min and Wong, Chau-Wai}, year={2018}, month={Nov} }
 @article{froehlich_atkins_wong_su_yin_2018, title={Encoding and decoding perceptually-quantized video content}, note={US Patent 9,936,199}, author={Froehlich, Jan and Atkins, Robin and Wong, Chau-Wai and Su, Guan-Ming and Yin, Peng}, year={2018}, month={Apr} }
 @inproceedings{liu_wong_wu_2018, title={Enhanced Geometric Reflection Models for Paper Surface Based Authentication}, DOI={10.1109/WIFS.2018.8630759}, abstractNote={Paper under the microscopic view has a rough surface formed by intertwisted wood fibers. Such roughness is unique on a specific location of the paper and is almost impossible to duplicate. Previous work has shown that commodity scanners and cameras are capable of capturing such intrinsic roughness in term of surface normal vectors for security and forensics applications. In this paper, we examine several candidate mathematical models for camera captured images of paper surfaces and compare the modeling accuracies with reference to the measurement by the confocal microscopy. Experimental results show that the model with distinct intensity bias for images captured from different viewpoints can provide the closest result to the confocal measurement. We discover that high-frequency subbands of reconstructed 3D surfaces are more powerful than the norm map in describing the uniqueness of a physical surface. We show through a practical paper surface based authentication system that incorporating these findings can improve the discrimination performance.}, booktitle={IEEE International Workshop on Information Forensics and Security (WIFS)}, author={Liu, Runze and Wong, Chau-Wai and Wu, Min}, year={2018}, pages={1–7} }
 @inproceedings{wong_hajj-ahmad_wu_2018, title={Invisible geo-location signature in a single image}, booktitle={IEEE International Conference on Acoustics, Speech and Signal Processing (ICASSP)}, author={Wong, Chau-Wai and Hajj-Ahmad, Adi and Wu, Min}, year={2018}, pages={1987–1991} }
 @article{zhao_zhan_wong_2018, title={Segmenting and Understanding Publics in a Social Media Information Sharing Network: An Interactional and Dynamic Approach}, volume={12}, DOI={10.1080/1553118x.2017.1379013}, abstractNote={ABSTRACT This study segments social media publics and analyzes their informational behaviors during organizational crises. With a public-centric perspective, our study highlights how social media publics interact with each other (i.e., interdependence) and share different information through crisis stages (i.e., dynamics). Following the situational approach to segmentation, we identify different types of social media publics (i.e., influentials, broadcasters, and followers) based on their informational behaviors and their positions in an information sharing network. Crisis managers are recommended to pay more attention to publics with higher influence, namely key influentials and broadcasters. In addition, we try to understand social media publics’ changing concerns by analyzing whether and how publics share messages of different themes and forms in different stages of a crisis. Crisis managers are recommended to customize crisis communication content to fit publics’ needs, prioritize organizational resources, and maximize positive communication effect. With big data from Chipotle’s E. coli crisis, we analyzed the Twitter activities surrounding this crisis over a 6-month period. Our segmentation receives initial support from the network analysis and content analysis on the Twitter data, which lays the foundation for effective social media crisis management.}, number={1}, journal={International Journal of Strategic Communication}, publisher={Routledge}, author={Zhao, Xinyan and Zhan, Mengqi and Wong, Chau-Wai}, year={2018}, pages={25–45} }
 @article{su_wong_chou_kottayil_2018, title={Signal reshaping approximation}, note={US Patent 10,080,026}, author={Su, Guan-Ming and Wong, Chau-Wai and Chou, Hsuan-Ting and Kottayil, Navaneeth KAMBALLUR}, year={2018}, month={Sep} }
 @article{wong_wu_2017, title={Counterfeit Detection Based on Unclonable Feature of Paper Using Mobile Camera}, volume={12}, DOI={10.1109/tifs.2017.2694404}, abstractNote={This paper studies the authentication problem of specific pieces of paper using mobile imaging devices. Prior work showing high matching accuracy has used the normal vector field, which serves as a unique, microscopic, physically unclonable feature of paper surfaces, estimated by consumer grade scanners. Industrial cameras were also used to capture the appearance of the surface rendered after the normal vector field based on the laws of optics under a semi-controlled lighting condition. In comparison, past explorations based on mobile cameras were very limited and have not had substantial success in obtaining consistent appearance images due to the uncontrolled nature of the ambient light. We show in this paper that images captured by mobile cameras can be used for authentication when the camera flashlight is exploited for creating a semi-controlled lighting condition. We have proposed new algorithms to demonstrate that the normal vector field of paper surface can be estimated by using multiple camera-captured images of different viewpoints. Perturbation analysis shows that the proposed method is robust to inaccurate estimates of camera locations, and a matching accuracy of  $10^{-\textrm {4}}$  in equal error rate can be achieved using 6 to 8 images under a lab-controlled ambient light environment. Our findings can relax the restricted imaging setups and enable paper authentication under a more casual, ubiquitous setting with a mobile imaging device, which may facilitate duplicate detection of paper documents and counterfeit mitigation of merchandise packaging.}, number={8}, journal={IEEE Transactions on Information Forensics and Security}, publisher={Institute of Electrical and Electronics Engineers (IEEE)}, author={Wong, Chau-Wai and Wu, Min}, year={2017}, month={Aug}, pages={1885–1899} }
 @inproceedings{zhao_zhan_wong_2017, title={Evolving publics, evolving messages: Analyzing publics’ information sharing network in a social-mediated crisis}, booktitle={67th Annual Conference of International Communication Association (ICA’17)}, author={Zhao, Xinyan and Zhan, Mengqi and Wong, Chau-Wai}, year={2017} }
 @inproceedings{zhu_wong_fu_wu_2017, title={Fitness Heart Rate Measurement Using Face Videos}, DOI={10.1109/ICIP.2017.8296632}, abstractNote={Recent studies showed that subtle changes in human's face color due to the heartbeat can be captured by digital video recorders. Most existing work focused on still/rest cases or those with relatively small motions. In this work, we propose a heart-rate monitoring method for fitness exercise videos. We focus on designing a highly precise motion compensation scheme with the help of the optical flow, and use motion information as a cue to adaptively remove ambiguous frequency components for improving the heart rates estimates. Experimental results show that our proposed method can achieve highly precise estimation with an average error of 1.1 beats per minute (BPM) or 0.58% in relative error.}, booktitle={IEEE International Conference on Image Processing (ICIP)}, author={Zhu, Qiang and Wong, Chau-Wai and Fu, Chang-Hong and Wu, Min}, year={2017} }
 @phdthesis{wong_2017, title={Micro Signal Extraction and Analytics}, author={Wong, Chau-Wai}, year={2017} }
 @inproceedings{zhao_yang_wong_2017, title={Toward a multilevel e-health engagement model: Analyzing trend for immigrants’ e-health engagement from 2008 to 2013}, booktitle={67th Annual Conference of International Communication Association (ICA’17)}, author={Zhao, Xinyan and Yang, Bo and Wong, Chau-Wai}, year={2017} }
 @inproceedings{we like the future more: examining the influence of crisis response strategies on public sentiment from a big data perspective_2017, booktitle={103rd Annual Convention of National Communication Association (NCA’17)}, year={2017} }
 @article{wong_su_wu_2016, title={Impact Analysis of Baseband Quantizer on Coding Efficiency for HDR Video}, volume={23}, DOI={10.1109/lsp.2016.2597175}, abstractNote={Digitally acquired high dynamic range (HDR) video baseband signal can take 10 to 12 bits per color channel. It is of economical importance to be able to reuse the legacy 8 or 10-bit video codecs to efficiently compress the HDR video. Linear or nonlinear mapping on the intensity can be applied to the baseband signal to reduce the dynamic range before the signal is sent to the codec, and we refer to this range reduction step as the baseband quantization. We show analytically and verify using test sequences that the existence of the baseband quantizer lowers the coding efficiency. Experiment shows that as the baseband quantizer strengthened by 1.6 bits, the drop of PSNR at high bitrate is up to 1.60 dB. Our result suggests that, in order to achieve high coding efficiency, video information reduction in terms of quantization error should be incurred in the video codec instead of on the baseband signal.}, number={10}, journal={IEEE Signal Processing Letters}, publisher={Institute of Electrical and Electronics Engineers (IEEE)}, author={Wong, Chau-Wai and Su, Guan-Ming and Wu, Min}, year={2016}, month={Oct}, pages={1354–1358} }
 @article{hajj-ahmad_wong_wu_2016, title={Information on the MAST ENF Power Signature Dataset}, author={Hajj-Ahmad, Adi and Wong, Chau-Wai and Wu, Min}, year={2016} }
 @inproceedings{wong_wu_2015, title={A Study on PUF characteristics for counterfeit detection}, DOI={10.1109/icip.2015.7351079}, abstractNote={Low-cost physically unclonable functions (PUFs) can be deployed with consumer products to deter counterfeiting. An intrinsic physical property - unique textures of paper or other surface - has received strong interest. Extrinsically introduced features, such as randomly positioned bubbles and fiber segments, have also been deployed in the industry to facilitate authentication. This paper carries out a study to gain a better understanding in the factors affecting the authentication performance, with a consideration of the friendliness under mobile imaging. Comparisons are made for paper-based PUFs of different characteristics. It is found that the density of foreground objects have a dominant impact on the authentication performance.}, booktitle={2015 IEEE International Conference on Image Processing (ICIP)}, publisher={IEEE}, author={Wong, Chau-Wai and Wu, Min}, year={2015}, month={Sep}, pages={1643–1647} }
 @inproceedings{wong_wu_2015, title={Counterfeit detection using paper PUF and mobile cameras}, DOI={10.1109/wifs.2015.7368579}, abstractNote={This work studies the paper authentication problem by exploiting optical features through mobile imaging devices to characterize the unique, physically unclonable properties of paper surface. Prior work showing high matching accuracy either used a consumer-level scanner for estimating a projected normal vector field of the surface of the paper as the feature for authentication, or used an industrial camera with controlled lighting to obtain an appearance image of the surface as the feature. In comparison, past explorations based on mobile cameras were very limited and have not had substantial success in obtaining consistent appearance images due to the uncontrolled nature of the ambient light. We show in this work that images captured by mobile cameras can be directly used for authentication by exploiting the camera flashlight to create a semi-controlled lighting condition. We have proposed new algorithms to demonstrate that the microscopic normal vector field of paper surface can be estimated by using multiple camera-captured images of different viewpoints. Our findings can relax the restricted imaging setups to enable paper authentication under a more casual, ubiquitous setting of a mobile imaging device, which may facilitate duplicate detection of paper documents and merchandise packaging.}, booktitle={2015 IEEE International Workshop on Information Forensics and Security (WIFS)}, publisher={IEEE}, author={Wong, Chau-Wai and Wu, Min}, year={2015}, month={Nov} }
 @inproceedings{su_hajj-ahmad_wong_garg_wu_2014, title={ENF Signal Induced by Power Grid}, DOI={10.1145/2660579.2660588}, abstractNote={Multiple videos capturing the same scene from possibly different viewing angles may be synthesized for novel immersive experience. Synchronization is an important task for such applications involving multiple pieces of audio-visual data. In this work, we exploit the electric network frequency (ENF) signal inherently embedded in the soundtrack and/or image sequence of video to temporally align video recordings. ENF is the supply frequency of power distribution networks in a power grid. Its value fluctuates slightly from its nominal value of 50 Hz or 60 Hz, and the fluctuation trends stay consistent within the same grid. Audio and video recordings that are created in areas of electric activities may capture the ENF signal due to electromagnetic interferences and other physical phenomena. We propose to synchronize video recordings by aligning the embedded ENF signals. Without major constraints on viewing angle and camera calibration as many existing methods impose, the proposed approach emerges as a new synchronization modality.}, booktitle={Proceedings of the 2nd ACM International Workshop on Immersive Media Experiences - ImmersiveMe '14}, publisher={ACM Press}, author={Su, Hui and Hajj-Ahmad, Adi and Wong, Chau-Wai and Garg, Ravi and Wu, Min}, year={2014} }
 @inproceedings{su_hajj-ahmad_wong_garg_wu_2014, title={ENF signal induced by power grid: A new modality for video synchronization}, booktitle={ACM International Workshop on Immersive Media Experiences}, author={Su, Hui and Hajj-Ahmad, Adi and Wong, Chau-Wai and Garg, Ravi and Wu, Min}, year={2014}, pages={13–18} }
 @article{wong_siu_2011, title={Analysis of Dyadic Approximation Error for Hybrid Video Codecs With Integer Transforms}, volume={20}, DOI={10.1109/tip.2011.2134105}, abstractNote={In this paper, we present an analysis of the dyadic approximation error introduced by the integerization of transform coding in H.264/AVC-like codecs. We derive the analytical formulations for dyadic approximation error and nonorthogonality error. We further classify the dyadic approximation error into a “system error” and a “nonflat error,” and proposed two models for them. We found that the “nonflat error” has a substantial impact on video quality if the number of shifting bits at decoder side (DQ_BITS) is small. We also give a theoretical justification on why scaling factors at encoder side are better to be adapted to the rescaling factors at decoder side in H.264/AVC-like codecs.}, number={10}, journal={IEEE Transactions on Image Processing}, publisher={Institute of Electrical and Electronics Engineers (IEEE)}, author={Wong, Chau-Wai and Siu, Wan-Chi}, year={2011}, month={Oct}, pages={2780–2787} }
 @article{wong_siu_2011, title={Comments on "2-D Order-16 Integer Transforms for HD Video Coding}, volume={21}, DOI={10.1109/tcsvt.2011.2129110}, abstractNote={In a recent paper, Dong proposed a set of order-16 nonorthogonal integer cosine transforms (NICTs). They proved that the reconstruction error caused by the nonorthogonality is negligible as compared to the error caused by the quantization. However, we would like to point out three problems found in derivations and also give two comments. Nevertheless, the problems are defects only, hence do not affect the overall justifications to the proposed NICT. This letter is to enhance and clarify the proof of Dong 's work.}, number={11}, journal={IEEE Transactions on Circuits and Systems for Video Technology}, publisher={IEEE}, author={Wong, Chau-Wai and Siu, Wan-Chi}, year={2011}, month={Nov}, pages={1765–1767} }
 @article{wong_siu_2011, title={Transform Kernel Selection Strategy for the H.264/AVC and Future Video Coding Standards}, volume={21}, DOI={10.1109/tcsvt.2011.2133190}, abstractNote={In this paper, we propose a new discrete cosine transform (DCT)-like kernel IK(5, 7, 3) and revitalize another DCT-like kernel IK(13, 17, 7) for the transform coding process of hybrid video coding. Making use one of these kernels together with the H.264/AVC kernel IK(1, 2, 1), we are able to design new multiple-kernel schemes which give better coding performance over that of the conventional approaches. All these schemes make use of the adaptive kernel mechanism at macroblock-level (MB-AKM), which requires heavy computation during the encoding process. We subsequently discovered that a rate-distortion feature extracted from a pair of kernels gives an intrinsic property that can be used to select a better kernel for a two-kernel MB-AKM system. This is a powerful tool with theoretical interest and practical uses. In order to reduce computation substantially, we make use of this tool to make an analysis and design of a frame-level adaptive kernel mechanism and come up with a simple solution that the kernel IK(1, 2, 1) be used for I-frames and P-frames and the kernel IK(5, 7, 3) be used for B-frames coding. This proposed frame-based AKM gives similar, or even better, performance as the proposed macroblock-based AKM. Furthermore, it substantially reduces computation and certainly gives a good improvement in terms of the PSNR and bitrate compared to those obtained from the H.264/AVC default scheme and other MB-AKM schemes available in the literature.}, number={11}, journal={IEEE Transactions on Circuits and Systems for Video Technology}, publisher={IEEE}, author={Wong, Chau-Wai and Siu, Wan-Chi}, year={2011}, month={Nov}, pages={1631–1645} }
 @phdthesis{wong_2010, title={Adaptive integer kernels and dyadic approximation error analysis for state-of-the-art video codecs}, school={The Hong Kong Polytechnic University}, author={Wong, Chau-Wai}, year={2010} }
 @inproceedings{wong_siu_2009, title={Transform kernel selection strategy for the H.264}, booktitle={Annual Summit and Conference, APSIPA}, author={Wong, Chau-Wai and Siu, Wan-Chi}, year={2009}, pages={64–70} }
 @article{hajj-ahmad_wong_wu, title={Information on the MAST ENF Power Signature Datasets Updated: May 2016}, author={Hajj-Ahmad, Adi and Wong, Chau-Wai and Wu, Min} }