Khalid Tahboub

The use of asymmetric numeral systems as an accurate replacement for Huffman coding

Entropy coding is an integral part of most data compression systems. Huffman coding (HC) and arithmetic coding (AC) are two of the most widely used coding methods. HC can process a large symbol alphabet at each step allowing for fast encoding and decoding. However, HC typically provides suboptimal data rates due to its inherent approximation of symbol probabilities to powers of 1 over 2. In contrast, AC uses nearly accurate symbol probabilities, hence generally providing better compression ratios. However, AC relies on relatively slow arithmetic operations making the implementation computationally demanding. In this paper we discuss asymmetric numeral systems (ANS) as a new approach to entropy coding. While maintaining theoretical connections with AC, the proposed ANS-based coding can be implemented with much less computational complexity. While AC operates on a state defined by two numbers specifying a range, an ANS-based coder operates on a state defined by a single natural number such that the x ∈ ℕ state contains ≈ log2(x) bits of information. This property allows to have the entire behavior for a large alphabet summarized in the form of a relatively small table (e.g. a few kilobytes for a 256 size alphabet). The proposed approach can be interpreted as an equivalent to adding fractional bits to a Huffman coder to combine the speed of HC and the accuracy offered by AC. Additionally, ANS can simultaneously encrypt a message encoded this way. Experimental results demonstrate effectiveness of the proposed entropy coder.

Automatic detection of abnormal human events on train platforms

Video surveillance systems that contain a large number of cameras makes the continuous monitoring of the video feeds nearly an impossible task. A transit or transportation authority usually deploys a video surveillance system to monitor and identify events in the system such as crowd behavior and crime. In this paper we present a method for automatically detecting people jumping or falling off a train platform. An experimental evaluation is described using a dataset that was recorded at a train station.

A web-based video annotation system for crowdsourcing surveillance videos

Video surveillance systems are of a great value to prevent threats and identify/investigate criminal activities. Manual analysis of a huge amount of video data from several cameras over a long period of time often becomes impracticable. The use of automatic detection methods can be challenging when the video contains many objects with complex motion and occlusions. Crowdsourcing has been proposed as an effective method for utilizing human intelligence to perform several tasks. Our system provides a platform for the annotation of surveillance video in an organized and controlled way. One can monitor a surveillance system using a set of tools such as training modules, roles and labels, task management. This system can be used in a real-time streaming mode to detect any potential threats or as an investigative tool to analyze past events. Annotators can annotate video contents assigned to them for suspicious activity or criminal acts. First responders are then able to view the collective annotations and receive email alerts about a newly reported incident. They can also keep track of the annotators’ training performance, manage their activities and reward their success. By providing this system, the process of video analysis is made more efficient.

An HEVC compressed domain content-based video signature for copy detection and video retrieval

Video sharing platforms and social networks have been growing very rapidly for the past few years. The rapid increase in the amount of video content introduces many challenges in terms of copyright violation detection and video search and retrieval. Generating and matching content-based video signatures, or fingerprints, is an effective method to detect copies or “near-duplicate” videos. Video signatures should be robust to changes in the video features used to characterize the signature caused by common signal processing operations. Recent work has focused on generating video signatures based on the uncompressed domain. However, decompression is a computationally intensive operation. In large video databases, it becomes advantageous to create robust signatures directly from the compressed domain. The High Efficiency Video Coding (HEVC) standard has been recently ratified as the latest video coding standard and wide spread adoption is anticipated. We propose a method in which a content-based video signature is generated directly from the HEVC-coded bitstream. Motion vectors from the HEVC-coded bitstream are used as the features. A robust hashing function based on projection on random matrices is used to generate the hashing bits. A sequence of these bits serves as the signature for the video. Our experimental results show that our proposed method generates a signature robust to common signal processing techniques such as resolution scaling, brightness scaling and compression.

Image-Like 2D Barcodes Using Generalizations of the Kuznetsov–Tsybakov Problem

In this paper, we propose a novel method for generating visually appealing two-dimensional (2D) barcodes that resemble meaningful images to human observers. The technology of 2D barcodes, currently dominated by quick response codes, is widely adopted in many applications, including product tracking, document management, and general marketing. Such barcodes typically lack user friendly appearance and do not convey any visual significance to human observers. The proposed method addresses this problem by allowing 2D barcodes to resemble an arbitrary image or a logo. Our method is based on a generalization of the Kuznetsov-Tsybakov problem that served as a foundation for wet paper codes, commonly adopted in digital steganography. We introduce weaker statistical constraints to obtain additional flexibility allowing the barcode to assume the appearance of an arbitrary pattern. This paper provides the theoretical analysis of the proposed coding framework and a practical algorithm for rapid approximation of the optimal code. We also discuss the introduction of error correction capabilities, and experimentally evaluate a prototype implementation in a smartphone-based acquisition scenario.

Superpixels shape analysis for carried object detection

Video surveillance systems generate enormous amounts of data which makes the continuous monitoring of video a very difficult task. Re-identification of subjects in video surveillance systems plays a significant role in public safety. Recent work has focused on appearance modeling and distance learning to establish correspondence between images. However, real-life scenarios suggest that the majority of clothing worn tends to be non-discriminative. Attributes- based re-identification methods try to solve this problem by incorporating semantic attributes which are mid-level features learned a prior. In this paper we present a framework to recognize attributes with applications to carried objects detection. We present a supervised approach based on the contours and shapes of superpixels and histogram of oriented gradients. An experimental evaluation is described using a dataset that was recorded at the Greater Cleveland Regional Transit Authority.

Automated crowd flow estimation enhanced by crowdsourcing

Video surveillance systems that contain a large number of cameras makes the continuous monitoring of the video feeds nearly an impossible task. If the information from these many cameras is to be exploited automatic video analytic techniques must be developed. In this paper, we present improvements to a previously developed crowd flow estimation method. We use crowdsourcing techniques to enhance the performance. An experimental evaluation is conducted using publicly available datasets.

Generalizations of the Kuznetsov-Tsybakov problem for generating image-like 2D barcodes

Many two-dimensional (2D) barcodes, such as quick response (QR) codes, lack user-friendly appearance. Our goal in this paper is to generate 2D barcodes that “look” like recognizable images or logos. Standard steganographic methods hide a message (payload) in an image usually by modifying bits in a specific way using predetermined pixels of the image. This approach cannot be directly used for very low bit rates commonly used in 1 bit per pixel 2D barcodes. It is possible to produce barcodes in which the grayness of a pixel in an image is interpreted as the probability of assigning a value (black or white) to the corresponding pixel of the encoded message (payload). This can be viewed as statistical constraints enforced on the encoded bit-sequence. Using an information theoretic approach, Kuznetsov and Tsybakov have shown that this can be done for a specific case of constraints almost without any loss of capacity. In this paper, we propose generalizations of this approach with weaker constraints as an application to generating 2D barcodes that resemble images. We describe a coding framework, various types of constraints, a practical approximation and some example 2D barcodes generated from our implementation.

An intelligent crowdsourcing system for forensic analysis of surveillance video

Video surveillance systems are of a great value for public safety. With an exponential increase in the number of cameras, videos obtained from surveillance systems are often archived for forensic purposes. Many automatic methods have been proposed to do video analytics such as anomaly detection and human activity recognition. However, such methods face significant challenges due to object occlusions, shadows and scene illumination changes. In recent years, crowdsourcing has become an effective tool that utilizes human intelligence to perform tasks that are challenging for machines. In this paper, we present an intelligent crowdsourcing system for forensic analysis of surveillance video that includes the video recorded as a part of search and rescue missions and large-scale investigation tasks. We describe a method to enhance crowdsourcing by incorporating human detection, re-identification and tracking. At the core of our system, we use a hierarchal pyramid model to distinguish the crowd members based on their ability, experience and performance record. Our proposed system operates in an autonomous fashion and produces a final output of the crowdsourcing analysis consisting of a set of video segments detailing the events of interest as one storyline.

Person re-identification using a patch-based appearance model

Person re-identification is the process of recognizing a person across a network of cameras with non-overlapping fields of view. In this paper we present an unsupervised multi-shot approach based on a patch-based dynamic appearance model. We use deformable graph matching for person re-identification using histograms of color and texture as features of nodes. Each graph model spans multiple images and each node is a local patch in the shape of a rectangle. We evaluate our proposed method on publicly available PRID 2011 and iLIDS-VID databases.