C.N. Canagarajah

C.N. Canagarajah
University of Bristol | UB · Merchant Venturers School of Engineering

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129
Publications
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1,937
Citations

Publications

Publications (129)
Article
In this paper, the problem of efficiently allocating wireless resources to support multiple scalable video sequences over a downlink cognitive radio network is addressed. We consider the coarse grain scalable (CGS) and medium grain scalable (MGS) extension of the H.264 standard as the encoding method and propose to perform a per-subcarrier transmit...
Article
Full-text available
Resource allocation schemes for orthogonal frequency division multiple access- (OFDMA-) based cognitive radio (CR) networks that impose minimum and maximum rate constraints are considered. To demonstrate the practical application of such systems, we consider the transmission of scalable video sequences. An integer programming (IP) formulation of th...
Conference Paper
Full-text available
The performance of an OFDM system can be improved by performing per-subcarrier antenna selection, which facilitates the exploitation of frequency and spatial diversity in the wireless channel. In this paper, we extend the concept of per-subcarrier antenna selection to a multiuser cognitive radio environment and present a practical subcarrier and an...
Conference Paper
Full-text available
Super-resolution and frame interpolation enhance low resolution low-framerate videos. Such techniques are especially important for limited bandwidth communications. This paper proposes a novel technique to up-scale videos compressed with H.264 at low bit-rate both in spatial and temporal dimensions. A quantisation noise model is used in the super-r...
Conference Paper
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The aim of this paper is to introduce a novel statistical model-based image fusion method for Synthetic Aperture Radar (SAR) and optical images. The current fusion algorithms are effective only in specific areas of the scene. Hence, the fused image may not contain enough information for subsequent processing like classification and feature extracti...
Conference Paper
This paper proposes a rate controlled redundancy-adaptive multiple description video coding method. The method adjusts the level of redundancy allocated to each macroblock based on an end to end distortion model that takes into account the effects of error propagation and concealment. Rate control at the macroblock level, ensures that the total bit...
Conference Paper
Full-text available
This paper aims to combine adaptive subcarrier allocation and bit loading with the transmission of the H.264 SVC (Scalable Video Coding) encoded video sequences in order to increase the number of supported users in the system and provide the best quality of service (QoS) to the subscribers. We initially assume that the number of calls at the base s...
Article
Image fusion involves combining multiple images of differing modalities (e.g. infrared and visible light radiation) to create a composite that contains complementary information from the inputs. Most methods of fused image assessment have involved some kind of subjective quality rating, which is then correlated with computational metrics. A differe...
Article
Full-text available
This paper presents a novel framework to achieve scalable multiview image compression and view synthesis. The open-loop wavelet-lifting scheme for geometric filtering has been exploited to achieve signal-to-noise ratio scalability and view-type scalability (mono, stereo, or multiview). Spatial scalability is achieved by employing in-band prediction...
Article
The increasing availability and deployment of imaging sensors operating in multiple spectral bands has led to a large research effort in image fusion, resulting in a plethora of pixel-level image fusion algorithms. However, the cognitive aspects of multisensor image fusion have not received much attention in the development of these methods. In thi...
Article
The combining of visible light and infrared visual representations occurs naturally in some creatures, including the rattlesnake. This process, and the wide-spread use of multi-spectral multi-sensor systems, has influenced research into image fusion methods. Recent advances in image fusion techniques have necessitated the creation of novel ways of...
Article
We propose a multicue gaze prediction framework for open signed video content, the benefits of which include coding gains without loss of perceived quality. We investigate which cues are relevant for gaze prediction and find that shot changes, facial orientation of the signer and face locations are the most useful. We then design a face orientation...
Conference Paper
This paper proposes a gaze prediction model for open signed video content. A face detection algorithm is used to locate faces across each frame in both profile and frontal orientations. A grid-based likelihood ratio track before detect routine is used to predict the orientation of the signer's head, which allows the gaze location to be localised to...
Conference Paper
Optical flow forms an important initial processing stage for many machine vision tasks. A framework is presented for the recovery of dense optical flows from image sequences containing large motions. Sparse feature correspondences are used to assign multiple optical flow hypotheses to each image pixel which are then independently refined to produce...
Conference Paper
This work explores the potential of sharing different arithmetic hardware operators tightly coupled to the integer pipeline of the open-source LEON3 processor. The idea is to map these modules to the same silicon area saving power consumption and area utilisation. The same strategy can be used to extend the architecture of processors optimized for...
Conference Paper
Optical flow forms an important initial processing stage for many machine vision tasks. A framework is presented for the recovery of dense optical flows from image sequences containing large motions. Sparse feature correspondences are used to assign multiple candidate optical flows to each image pixel. This set of flows is then augmented with addit...
Chapter
In this chapter, we present a novel multimodal image fusion algorithm using the Independent Component Analysis (ICA). Region-based fusion of ICA coefficients is implemented, in which the mean absolute value of ICA coefficients is used as an activity indicator for the given region. The ICA coefficients from given regions are consequently weighted us...
Article
Accurate quality assessment of fused images, such as combined visible and infrared radiation images, has become increasingly important with the rise in the use of image fusion systems. We bring together three approaches, applying two objective tasks (local target analysis and global target location) to two scenarios, together with subjective qualit...
Article
Mobility tracking based on data from wireless cellular networks is a key challenge that has been recently investigated both from a theoretical and practical point of view. This paper proposes Monte Carlo techniques for mobility tracking in wireless communication networks by means of received signal strength indications. These techniques allow for a...
Conference Paper
Full-text available
Volumetric reconstruction is one of the 3D processing technologies for multi-view systems. The existing methods of volume reconstruction have been proposed by exploiting the original views with many constraints. These algorithms may not be suitable for the distributed camera system where multiple views are transmitted via lossy networks before proc...
Conference Paper
Full-text available
Advances in fusion of multi-sensor inputs have necessitated the creation of more sophisticated fused image assessment techniques. The current work extends previous studies investigating participant accuracy in tracking individuals in a video sequence. Participants were shown visible and IR videos individually and the two video inputs side-by-side,...
Conference Paper
This paper proposes a generalised framework for model based, context dependent video coding, based on exploitation of characteristics of the human visual system. The system utilises variable quality coding, based on a map which is created using context dependent rules. The technique is demonstrated for a specific video context, namely open signed c...
Conference Paper
Full-text available
This paper investigates the impact of pixel-level fusion of videos from visible (VIZ) and infrared (IR) surveillance cameras on object tracking performance, as compared to tracking in single modality videos. Tracking has been accomplished by means of a particle filter which fuses a colour cue and the structural similarity measure (SSIM). The highes...
Article
A novel objective non-reference metric for multimodal image sensor fusion is presented. Using the joint segmentation of the input images and entropy of the regions as the priority, an `ideal' fused image is obtained. The metric is based on computing how accurately the important regions from the input images are transferred into the fused image. Exp...
Article
Absolute value coding is introduced as a method for significantly reducing temporal drift within a motion compensated predictive video codec in the presence of loss. Drift reduction both improves error resilience and enables scalability by omission of parts of the bit-stream. In conjunction with matching pursuits, the system can be used to provide...
Article
A gaze location prediction model is presented for open signed broadcast video based on actual eye tracking data with fluent British sign language users. The model is used for formulating a variable quality coding approach of such video which is shown to be capable of offering up to 30% reduction in bit rate with little or no discernible effect on t...
Article
The increased interest in image fusion (combining images of two or more modalities such as infrared and visible light radiation) has led to a need for accurate and reliable image assessment methods. Previous work has often relied upon subjective quality ratings combined with some form of computational metric analysis. However, we have shown in prev...
Article
Full-text available
This paper describes the main results of a recent investigation of wavelet- based algorithms for fusion of visible and infrared surveillance image sequences used in various scenarios. The concept of adaptive image fusion where the fusion engine adapts to multiple streams of input images and tries to achieve optimal fu- sion performance,under real-t...
Article
As multimedia content is rapidly increasing everyday, the availability of indexing metadata such as MPEG-7 descriptors becomes increasingly important for accessibility purposes. However, the use of this indexing metadata in improving coding efficiency has rarely been explored. A novel fast mode decision algorithm for H.264/AVC encoders based on the...
Article
Subpixel motion estimation plays an important role in compression efficiency within modern video codecs such as MPEG2, MPEG4, and H.264. Subpixel motion estimation is implemented within these standards using interpolated values at 1/2 or 1/4 pixel accuracy. Such interpolation gives a good reduction in residual energy for each predicted macroblock a...
Conference Paper
A real-time, non-iterative, multi-view depth estimation algorithm is presented. Based on the postulate that regions of similar colour in an image have similar depths, a novel filter is proposed which seeks to minimize the error associated with a given depth while preserving possible depth discontinuities at colour boundaries.
Conference Paper
Full-text available
In this paper, we propose a novel volumetric representation for a sparse set of calibrated multi-view images of a non-Lambertian scene. The depth map of each reference view is registered into a volume and a simple algorithm to shape the volume is introduced. Particular colours are defined for each voxel to render a smooth and realistic image. Synth...
Article
Delay sensitive video transmission over error prone networks can suffer from packet erasures when channel conditions are not favorable. Use of error concealment (EC) at the video decoder is necessary in such cases to prevent error induced artefacts making the affected video frames visibly intolerable. This paper proposes an EC method that incorpora...
Conference Paper
Full-text available
A number of segmentation techniques are compared with regard to their usefulness for region-based image and video fusion. In order to achieve this, a new multi-sensor data set is introduced containing a variety of infra-red, visible and pixel fused images together with manually produced "ground truth" segmentations. This enables the objective compa...
Article
Full-text available
This paper addresses the problem of po-sition localisation of mobile nodes in ad hoc wire-less networks based on received signal strength in-dicator measurements. Node mobility is modelled as a linear system driven by a discrete command Markov process. Self-localisation of mobile nodes is performed via an Interacting Multiple Model fil-ter consisti...
Article
The prevalence of image fusion---the combination of images of different modalities, such as visible and infrared radiation---has increased the demand for accurate methods of image-quality assessment. The current study used a signal-detection paradigm, identifying the presence or absence of a target in briefly presented images followed by an energy...
Article
Full-text available
Image fusion is the process of combining images of differing modalities, such as visible and infrared (IR) images. Significant work has recently been carried out comparing methods of fused image assessment, with findings strongly suggesting that a task-centred approach would be beneficial to the assessment process. The current paper reports a pilot...
Article
A novel image fusion performance metric using mutual information is proposed. The metric is based on Tsallis entropy, which is a one-parameter generalisation of Shannon entropy. Experimental results have confirmed that the proposed metric outperforms the standard MI metric by correlating better with the subjective quality of fused images.
Conference Paper
Full-text available
A novel algorithm for disparity/depth estimation from multi-view images is presented. A dynamic programming approach with window-based correlation and a novel cost function is proposed. The smoothness of disparity/depth map is embedded in dynamic programming approach, whilst the window-based correlation increases reliability. The enhancement method...
Conference Paper
Full-text available
This paper investigates how the object tracking performance is affected by the fusion quality of videos from visible (VIZ) and infrared (IR) surveillance cameras, as compared to tracking in single modality videos. The videos have been fused us-ing the simple averaging, and various multiresolution techniques.Tracking has been accomplished by means o...
Article
Full-text available
This report details a data gathering ex- ercise carried out at the Eden Project in Cornwall, UK. A large number of dierent sensors (including infra-red, standard and high definition, and lower quality visible sensors) were used to film simultane- ously various scenes and scenarios. Ground truth data and meta-data were also recorded. We be- lieve we...
Conference Paper
Multiple reference motion compensated prediction achieves significant prediction gains, but at the expense of a significant increase in computational complexity. This paper investigates and compares the performance of a number of fast motion estimation techniques when extended to work for multiple reference prediction. In general, algorithms that a...
Conference Paper
Image fusion is the process of extracting meaningful visual information from two or more images and combining them to form one fused image. Image fusion is important within many different image processing fields from remote sensing to medical applications. Previously, real valued wavelet transforms have been used for image fusion. Although this tec...
Conference Paper
Full-text available
This paper presents a novel framework to achieve scalable multi-view image coding. As open loop operation, the wavelet lifting scheme for geometric filtering has been exploited to overcome the limitation of SNR scalability and to attain view scalability. The essential key for achieving the spatial scalability is the in-band prediction. It removes c...
Conference Paper
Full-text available
Image fusion is finding increasing application in areas such as medical imaging, remote sensing or military surveillance using sensor networks. Many of these applications demand highly compressed data combined with error resilient coding due to the characteristics of the communication channel. In this respect, JPEG2000 has many advantages over prev...
Conference Paper
Full-text available
We describe an image fusion algorithm for data exhibiting heavy tails with no convergent second- or higher-order moments. Our developments rely on recent results showing that wavelet decomposition coefficients of images are best modeled by alpha-stable distributions, a family of heavy-tailed densities. Thus, in the multiscale wavelet domain we deve...
Conference Paper
In rapidly deployable video surveillance networks, camera positions may be heavily constrained and coverage limited and often sparse. To enhance visualization, automatic depth estimation algorithms can be utilized to enable the synthesis of arbitrary views of the scene, offering a pseudo 'look-around' capability. In a wireless local area network, b...
Conference Paper
A number of lifting-based video coding schemes have been recently proposed for scalable video coding. We present a novel multi-view image codec based on a wavelet lifting scheme. The proposed lifting scheme with disparity compensated channel filtering is very efficient in terms of compression performance, memory requirements and implementation. We...
Article
Full-text available
The widespread use of image fusion - combining images of different modalities - is finding increasing application in f ields such as, for example, medical imaging, remote sensing and surveillance. C onsequently, the ability to assess the fused images accurately has become of gr eat importance. In this correspondence, the differences between convent...
Article
The use of robust watermarks for attack characterisation is an area of considerable potential which has been largely overlooked to date. The authors extend their earlier work on accurate attack characterisation using a double watermarking technique to include a larger library of attacks. It is shown that the complexity of the double watermarking te...
Conference Paper
Because of its high computational complexity, the process of motion estimation has become a bottleneck problem in many video applications, such as mobile video terminals and software-based video codecs. This has motivated the development of a number of fast motion estimation techniques. This paper briefly reviews reduced complexity motion estimatio...
Conference Paper
Warping-based motion estimation has been proposed in the literature to achieve higher video coding efficiency compared to conventional block-based motion estimation. This paper investigates the performance of warping-based methods at very low bit rates typical of mobile video communication applications. Simulation results show that despite their im...
Article
This paper proposes a low-complexity sub-pixel refinement to motion estimation based on full-search block matching algorithm (BMA) at integer-pixel accuracy. This algorithm eliminates the need to produce interpolated reference frames, which is may be too memory- and processor- intensive, for some real-time mobile applications. The algorithm assumes...
Article
This paper addresses two issues related to motion estimation using the block matching algorithms (BMA): (1) determining the reliability of the motion vectors of each block, and (2) imposing smoothness constraint to the motion vector field. We introduce a new robust reliability measure to represent the confidence level of the motion vector from the...
Article
This paper describes a new class of fused image dis-plays called hybrid fused displays. Such displays can be cre-ated by gradually transforming a fused image computed by one fusion method into another fused image computed by a different fusion method, either in the spatial domain or in another do-main. By defining either global image-to-image or lo...
Article
This paper focuses on a novel region-based image fusion method which facilitates increased flexibility with the def-inition of a variety of fusion rules. A dual-tree complex wavelet transform (DT-CWT) is used to segment the features of the in-put images, either jointly or separately, to produce a region map. Characteristics of each region are calcu...
Article
Originally used to extract simple shapes from images, the robustness of the Hough transform towards outliers has made it the method of choice for offline-feature extraction applications; however, its heavy computational load and memory requirement have prevented it from being applied in real-time applications. In the light of increasing processor s...
Conference Paper
Compared to block-based motion fields, pel-based (or dense) motion fields have been shown to provide improved quality in many applications. However, this improved performance is achieved at the expense of a significant increase in both computational complexity and motion overhead. In this paper, motion field interpolation (MFI) is proposed as a met...
Conference Paper
In this paper we describe a reduced complexity attack characterisation technique. A Bayesian framework is constructed, and the underlying distributions are assumed Gaussian. This allows quadratic discriminant functions to be used. This technique has the advantage over previous non-parametric techniques that histograms derived from Monte Carlo simul...
Conference Paper
The widespread adoption of digital video techniques has generated a requirement for authenticity verification in applications such as criminal evidence, insurance claims and commercial databases. The paper investigates the performance, effectivity and efficiency of a spatial digital watermark designed for video authentication. The embedded watermar...
Conference Paper
We propose the use of robust watermarks to enable the characterisation of attacks even after lossy compression, such as JPEG and JPEG2000. A previously constructed Bayesian framework is used to allow characterisation of attacks from a predetermined library, and the double watermarking technique as earlier proposed by the authors is employed to gene...
Article
The imminent arrival of mobile video telephony will enable deaf people to communicate - as hearing people have been able to do for a some time now - anytime/anywhere in their own language sign language. At low bit rates coding of sign language sequences is very challenging due to the high level of motion and the need to maintain good image quality...
Conference Paper
A novel system for gaze-contingent image analysis and multi-sensorial image display is described. The observer's scanpaths are recorded while viewing and analysing 2-0 or 3-0 (volumetric) images. A region-of-interest (ROI) centred around the current fixation point is simultaneously subjected to real-time image analysis algorithms to compute various...
Article
The segmentation of images into meaningful and homogenous regions is a key method for image analysis within applications such as content based retrieval. The watershed transform is a well established tool for the segmentation of images. However, watershed segmentation is often not effective for textured image regions that are perceptually homogeneo...
Article
For indoor and small cell urban environments the multipath activity is contained within a relatively short time window. Polarisation diversity offers additional diversity gain from independently fading signals, especially in channels where the system bandwidth is comparable with the channel coherence bandwidth, and hence limits the available freque...
Article
Full-text available
Automatic recognition of instrument type from raw audio data containing monophonic music is a fundamental problem for audio content analysis. There are many methods for the solution of this problem, which use common spectro-temporal properties like cepstral coefficients or spectral envelopes. A new method for instrument recognition utilising short-...
Conference Paper
Full-text available
UMTS (Universal Mobile Telecommunications System) spreading codes are only truly orthogonal in the absence of multipath delay and time offsets. In all practical channels the loss of orthogonality will result in the generation of non-zero cross-correlation products that can compromise the error performance of code division multiple access (CDMA) sys...
Article
The widespread adoption of digital video techniques has generated a requirement for authenticity verification in applications such as criminal evidence, insurance claims and commercial databases. This work addresses problems that arise from a spatial digital watermarking technique developed to detect frame reordering and dropping scenarios. It disc...
Conference Paper
The watershed transform is a well established tool for the segmentation of images. However, watershed segmentation is often not effective for textured regions that are perceptually homogeneous. Such regions are usually inaccurately over-segmented with no reference to any texture changes. We now introduce a novel concept of "texture gradient" implem...
Conference Paper
The widespread adoption of digital video techniques has generated a requirement for authenticity verification in applications such as criminal evidence, insurance claims and commercial databases. This work addresses problems that arise from a spatial digital watermarking technique developed to detect frame reordering and dropping scenarios. It disc...
Conference Paper
This paper proposes a novel low-complexity block-based global motion estimation algorithm for real-time digital video processing applications. The algorithm involves an 8×8 block-based local motion estimation followed by a least square method to obtain the global motion vector parameters. The translation-zoom global motion model with 3 parameters w...