Creat membership Creat membership
Sign in

Forgot password?

  • Forgot password?
    Sign Up
  • Confirm
    Sign In
home > search

Now showing items 1 - 16 of 24

  • A multi-metric approach for block-level video quality assessment

    Papadopoulos, Miltiadis Alexios   Katsenou, Angeliki, V   Agrafiotis, Dimitris   Bull, David R.  

    Developing an objective video quality metric that accurately estimates perceived video quality is challenging. Developing a metric that can additionally be embedded in the rate distortion optimization process of a video codec can be even harder given that decisions have to be made locally. In this paper, we present a method for combining a number of existing state of the art objective video quality metrics at the coding block level by employing a fusion of local content features for deciding how to best utilize the chosen metrics. Our results indicate promising performance in terms of the correlation of the developed locally-acting quality metric with the overall perceived quality of the video.
    Download Collect
  • QSAR without borders

    Muratov, Eugene N.   Bajorath, Jurgen   Sheridan, Robert P.   Tetko, Igor, V   Filimonov, Dmitry   Poroikov, Vladimir   Oprea, Tudor, I   Baskin, Igor I.   Varnek, Alexandre   Roitberg, Adrian   Isayev, Olexandr   Curtalolo, Stefano   Fourches, Denis   Cohen, Yoram   Aspuru-Guzik, Alan   Winkler, David A.   Agrafiotis, Dimitris   Cherkasov, Artem   Tropsha, Alexander  

    Prediction of chemical bioactivity and physical properties has been one of the most important applications of statistical and more recently, machine learning and artificial intelligence methods in chemical sciences. This field of research, broadly known as quantitative structure-activity relationships (QSAR) modeling, has developed many important algorithms and has found a broad range of applications in physical organic and medicinal chemistry in the past 55+ years. This Perspective summarizes recent technological advances in QSAR modeling but it also highlights the applicability of algorithms, modeling methods, and validation practices developed in QSAR to a wide range of research areas outside of traditional QSAR boundaries including synthesis planning, nanotechnology, materials science, biomaterials, and clinical informatics. As modern research methods generate rapidly increasing amounts of data, the knowledge of robust data-driven modelling methods professed within the QSAR field can become essential for scientists working both within and outside of chemical research. We hope that this contribution highlighting the generalizable components of QSAR modeling will serve to address this challenge.
    Download Collect
  • High Dynamic Range Video Compression Exploiting Luminance Masking

    Zhang, Yang   Naccari, Matteo   Agrafiotis, Dimitris   Mrak, Marta   Bull, David R.  

    The human visual system (HVS) exhibits nonlinear sensitivity to the distortions introduced by lossy image and video coding. This effect is due to the luminance masking, contrast masking, and spatial and temporal frequency masking characteristics of the HVS. This paper proposes a novel perception-based quantization to remove nonvisible information in high dynamic range (HDR) color pixels by exploiting luminance masking so that the performance of the High Efficiency Video Coding (HEVC) standard is improved for HDR content. A profile scaling based on a tone-mapping curve computed for each HDR frame is introduced. The quantization step is then perceptually tuned on a transform unit basis. The proposed method has been integrated into the HEVC reference model for the HEVC range extensions (HM-RExt), and its performance was assessed by measuring the bitrate reduction against the HM-RExt. The results indicate that the proposed method achieves significant bitrate savings, up to 42.2%, with an average of 12.8%, compared with HEVC at the same quality (based on HDR-visible difference predictor-2 and subjective evaluations).
    Download Collect

    The invention provides a method of controlling a video transmission system, the method comprising receiving an input indicative of a desired mode of operation, automatically configuring transmission parameters in dependence upon the desired mode of operation indicated by the received input and encoding and transmitting a video datastream over a communications channel using such transmission parameters. Also provided is a video transmission system comprising a video source operable to generate and output a video datastream, a user input device operable to receive a user input indicative of a desired mode of operation, a datastream encoder and transmitter unit operable to receive user input information from the user input device, to configure transmission parameters in dependence upon a desired mode of operation indicated by a received user input, and to encode and transmit a video datastream over a communications channel using transmission parameters.
    Download Collect
  • Gaze Location Prediction for Broadcast Football Video

    Cheng, Qin   Agrafiotis, Dimitris   Achim, Alin M.   Bull, David R.  

    The sensitivity of the human visual system decreases dramatically with increasing distance from the fixation location in a video frame. Accurate prediction of a viewer's gaze location has the potential to improve bit allocation, rate control, error resilience, and quality evaluation in video compression. Commercially, delivery of football video content is of great interest because of the very high number of consumers. In this paper, we propose a gaze location prediction system for high definition broadcast football video. The proposed system uses knowledge about the context, extracted through analysis of a gaze tracking study that we performed, to build a suitable prior map. We further classify the complex context into different categories through shot classification thus allowing our model to prelearn the task pertinence of each object category and build the prior map automatically. We thus avoid the limitation of assigning the viewers a specific task, allowing our gaze prediction system to work under free-viewing conditions. Bayesian integration of bottom-up features and top-down priors is finally applied to predict the gaze locations. Results show that the prediction performance of the proposed model is better than that of other top-down models that we adapted to this context.
    Download Collect
  • Flexible Adaptive Multiple Description Coding for Video Transmission

    Kamnoonwatana, Nawat   Agrafiotis, Dimitris   Canagarajah, C. Nishan  

    A channel adaptive multiple description video codec is presented with flexible redundancy allocation based on modeling and minimization of the end-to-end distortion. We employ a three-loop multiple description coding scheme for which we develop models that estimate the rate-distortion performance of the side encoders as well as the overall end-to-end distortion given channel statistics. A simple yet effective algorithm is formulated for determining appropriate levels of redundancy given a total bit rate and channel estimates in the form of packet error rates. The experimental results presented validate the proposed models over various channels conditions. The performance and adaptivity of the codec is evaluated through extensive simulations with a 2 x 2 wireless multiple input multiple output system. A gain of more than 10 dB can be achieved compared to a non-adaptive system and even larger gains can be had relative to typical single description transmissions.
    Download Collect
  • Image and video compression for HDR content

    Zhang, Yang   Reinhard, Erik   Agrafiotis, Dimitris   Bull, David R.  

    High Dynamic Range (HDR) technology can offer high levels of immersion with a dynamic range meeting and exceeding that of the Human Visual System (HVS). A primary drawback with HDR images and video is that memory and bandwidth requirements are significantly higher than for conventional images and video. Many bits can be wasted coding redundant imperceptible information. The challenge is therefore to develop means for efficiently compressing HDR imagery to a manageable bit rate without compromising perceptual quality. In this paper, we build on previous work of ours and propose a compression method for both HDR images and video, based on an HVS optimised wavelet subband weighting method. The method has been fully integrated into a JPEG 2000 codec for HDR image compression and implemented as a pre-processing step for HDR video coding (an H. 264 codec is used as the host codec for video compression). Experimental results indicate that the proposed method outperforms previous approaches and operates in accordance with characteristics of the HVS, tested objectively using a HDR Visible Difference Predictor (VDP). Aiming to further improve the compression performance of our method, we additionally present the results of a psychophysical experiment, carried out with the aid of a high dynamic range display, to determine the difference in the noise visibility threshold between HDR and Standard Dynamic Range (SDR) luminance edge masking. Our findings show that noise has increased visibility on the bright side of a luminance edge. Masking is more consistent on the darker side of the edge.
    Download Collect
  • Rate controlled redundancy-adaptive multiple description video coding

    Kamnoonwatana, Nawat   Agrafiotis, Dimitris   Canagarajah, Nishan  

    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 rate of all descriptions does not exceed the target rate. Results show that the proposed MDC codec can adapt very well to changing transmission conditions. Gains of up to 14 dB at high packet error rates (low SNR) were recorded when coupled with a MIMO architecture, with no perceptible performance deficit at low packet error rates (high SNR). 2011 Elsevier B.V. All rights reserved.
    Download Collect
  • Performance of OFDM-based massive MIMO OTFS systems for underwater acoustic communication

    Bocus, Mohammud Junaid   Doufexi, Angela   Agrafiotis, Dimitris  

    In this study, multi-user (MU) underwater acoustic communication is investigated using massive multiple-input multiple-output (MIMO) orthogonal frequency division multiplexing (OFDM)-based orthogonal time frequency space modulation (OTFS) systems. The performance of a 4-user scenario is evaluated over a simulated 1 km vertically-configured time-varying underwater acoustic channel (UAC) in terms of bit error rate and maximum achievable bit rate. Considering 64-QAM and frequency-domain pilot-based channel estimation, it is shown that the underwater vehicles employing the OFDM-based OTFS modulation outperform those using the conventional OFDM modulation in a dynamic UAC. The application of massive MIMO allows the four underwater vehicles to use the same time and frequency resources to transmit their information reliably to a surface station. Furthermore, it is shown that each underwater vehicle in the MU-massive MIMO transmission scenario can achieve an effective bit rate as high as 198.7 kbps over the 1 km UAC using four transmitting transducers.
    Download Collect

    Anantrasirichai, Nantheera   Agrafiotis, Dimitris   Bull, Dave  

    Systems with cheap/simple/power efficient encoders but complex decoders make applications such as low cost, low power remote sensors practical. Bandwidth considerations however are still an issue and compression efficiency has to remain high. In this paper, we present a distributed video codec (DVC) that we are developing with the aim of achieving such a low power paradigm at the cost of only a small compression performance deficit relative to the current state of the art, H.264. The proposed system employs spatial interleaving of KEY and Wyner-Ziv data which allows efficient side information (SI) generation through block-based error concealment, a Gray code that increases the accuracy of bit probability estimation, and a diversity scheme that produces more reliable results by exploiting multiple SI generated data. Simulation results show an improvement of the proposed scheme over H.264 intra coding of up to 1.5 dB. We additionally propose two mechanisms for selective parity bit feedback requests that can further reduce the WZ bitrate by up to 15%.
    Download Collect

    Anantrasirichai, Nantheera   Agrafiotis, Dimitris   Bull, Dave  

    This paper presents a concealment based approach to distributed video coding that uses hybrid Key/WZ frames via an FMO type interleaving of macroblocks. Our motivation stems from a previous work of ours that showed promising results relative to the more common approach of splitting the sequence in key and WZ frames. In this paper, we extend our previous scheme to the case of I-B-P frame structures and transform domain DVC. We additionally introduce a number of enhancements at the decoder including use of spatio-temporal concealment for generating the side information on a MB basis, mode selection for switching between the two concealment approaches and for deciding how the correlation noise is estimated, local (MB wise) correlation noise estimation and modified B frame quantisation. The results presented indicate considerable improvement (up to 30%) compared to corresponding frame extrapolation and frame interpolation schemes.
    Download Collect

    A temporal error concealment is described. A video stream comprises a current frame comprising a lost image region, and a reference frame. The method comprises forming a list of motion vector candidates, the list of motion vector candidates including a set of one or more motion vectors from the current frame and a set of one or more motion vectors from the reference frame; testing each of the motion vector candidates using a matching error measure; selecting a replacement motion vector from the list based on the matching error measures; and using the selected replacement motion vector to conceal the lost image region. A mode selection method is also described. A motion vector is used to identify a motion compensated reference image region in the reference frame. A motion compensated temporal activity of an image region in the current frame is calculated based on a comparison between the image region in the current frame and the motion compensated reference image region in the reference frame. A spatial or temporal error concealment mode is then selected based on the calculated temporal activity.
    Download Collect
  • Enhanced error concealment with mode selection

    Agrafiotis, Dimitris   Bull, David R.   Canagarajah, C. Nishan  

    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 incorporates enhanced temporal and spatial concealment elements, the use of which is controlled by a mode selection (MS) algorithm well matched to the characteristics of the temporal concealment approach. The performance of the individual enhancements and of the MS algorithm are compared with the respective features of the method employed in the H.264 joint model (JM) decoder and with other state of the art methods. The overall performance of the proposed method is shown to offer significant gains (up to 9 dB) compared to that of the JM decoder for a wide range of natural and animation image sequences without any considerable increase in complexity.
    Download Collect
  • Multiple priority region of interest coding with H.264

    Agrafiotis, Dimitris   Bull, David R.   Canagarajah, Nishan   Kamnoonwatana, Nawat  

    This paper describes a modified rate control algorithm for H.264 that can accommodate multiple priority levels given a region of interest (RoI). The modified method allows better control of the quality of the RoI and gradual variation of the quality in the rest of the video frame through a bit redistribution process that is based on a number of parameters, including characteristics of the RoI, user input and perceptual factors.
    Download Collect
  • A perceptually optimised video coding system for sign language communication at low bit rates

    Agrafiotis, Dimitris   Canagarajah, Nishan   Bull, David R.   Kyle, Jim   Seers, Helen   Dye, Matthew  

    The ability to communicate remotely through the use of video as promised by wireless networks and already practised over fixed networks, is for deaf people as important as voice telephony is for hearing people. Sign languages are visual-spatial languages and as such demand good image quality for interaction and understanding. In this paper, we first analyse the sign language viewer's eye-gaze, based on the results of an eye-tracking study that we conducted, as well as the video content involved in sign language person-to-person communication. Based on this analysis we propose a sign language video coding system using foveated processing, which can lead to bit rate savings without compromising the comprehension of the coded sequence or equivalently produce a coded sequence with higher comprehension value at the same bit rate. We support this claim with the results of an initial comprehension assessment trial of such coded sequences by deaf users. The proposed system constitutes a new paradigm for coding sign language image sequences at limited bit rates. (C) 2006 Elsevier B.V. All rights reserved.
    Download Collect
  • A video error resilience redundant slices algorithm and its performance relative to other fixed redundancy schemes

    Ferre, Pierre   Agrafiotis, Dimitris   Bull, David  

    In this paper, a redundant picture formation algorithm that takes into account a given redundancy rate constraint is presented for error resilient wireless video transmission without reliance on retransmissions. The algorithm assigns priorities to macroblocks (MBs) according to two suggested metrics and ranks MBs accordingly. The first metric is based on an end-to-end distortion model and aims at maximising the reduction in distortion per redundancy bit. The end-to-end distortion accounts for the effects of error propagation, mismatch between the primary and redundancy description and error concealment. MBs providing large distortion reduction for fewer bits spent are assigned a higher priority. The second metric employs the variance of the motion vectors of a macroblock and those of its neighbouring blocks. Results show that the rate distortion metric outperforms other examined metrics by up to 2 dB. A comparison with other error resilience schemes, such as loss adaptive-rate distortion optimisation (LA-RDO) and cross packet forward error correction (FEC), is also presented. Results show that our approach outperforms the LA-RDO solution. Cross packet FEC provides better performance in the presence of random packet losses. However, results show that our approach can tackle bursty losses better. With bursty errors, the correction capabilities of the Reed-Solomon codes can be exceeded, and the availability of a coarse representation of the coded macroblocks, through a redundant slice scheme, can offer performance gains of up to 1 dB. (C) 2010 Elsevier B.V. All rights reserved.
    Download Collect
1 2


If you have any feedback, Please follow the official account to submit feedback.

Turn on your phone and scan

Submit Feedback