Mesh-based video coding for low bit-rate communications

In this paper, a new method for low bit-rate content-adaptive mesh-based video coding is proposed. Intra-frame coding of this method employs feature map extraction for node distribution at specific threshold levels to achieve higher density placement of initial nodes for regions that contain high frequency features and conversely sparse placement of initial nodes for smooth regions. Insignificant nodes are largely removed using a subsequent node elimination scheme. The Hilbert scan is then applied before quantization and entropy coding to reduce amount of transmitted information. For moving images, both node position and color parameters of only a subset of nodes may change from frame to frame. It is sufficient to transmit only these changed parameters. The proposed method is well-suited for video coding at very low bit rates, as processing results demonstrate that it provides good subjective and objective image quality at a lower number of required bits

Improved Image Partitioning for Compression and Representation using the Lab Color Space in the LAR Image Codec

International audienceThe LAR codec is an advanced image compression method relying on a quadtree partitioning of the image. The partitioning strongly impacts the LAR codec efficiency and enables both compression and representation efficiency. In order to increase the perceptual representation abilities without penalizing the compression efficiency we introduce and evaluate two partitioning criteria working in the Lab color space. These criteria are confronted to the original criterion and their compression and robustness performances are analyzed

Research and developments of Dirac video codec

This thesis was submitted for the degree of Doctor of Philosophy and was awarded by Brunel University.In digital video compression, apart from storage, successful transmission of the compressed video data over the bandwidth limited erroneous channels is another important issue. To enable a video codec for broadcasting application, it is required to implement the corresponding coding tools (e.g. error-resilient coding, rate control etc.). They are normally non-normative parts of a video codec and hence their specifications are not defined in the standard. In Dirac as well, the original codec is optimized for storage purpose only and so, several non-normative part of the encoding tools are still required in order to be able to use in other types of application. Being the "Research and Developments of the Dirac Video Codec" as the research title, phase I of the project is mainly focused on the error-resilient transmission over a noisy channel. The error-resilient coding method used here is a simple and low complex coding scheme which provides the error-resilient transmission of the compressed video bitstream of Dirac video encoder over the packet erasure wired network. The scheme combines source and channel coding approach where error-resilient source coding is achieved by data partitioning in the wavelet transformed domain and channel coding is achieved through the application of either Rate-Compatible Punctured Convolutional (RCPC) Code or Turbo Code (TC) using un-equal error protection between header plus MV and data. The scheme is designed mainly for the packet-erasure channel, i.e. targeted for the Internet broadcasting application. But, for a bandwidth limited channel, it is still required to limit the amount of bits generated from the encoder depending on the available bandwidth in addition to the error-resilient coding. So, in the 2nd phase of the project, a rate control algorithm is presented. The algorithm is based upon the Quality Factor (QF) optimization method where QF of the encoded video is adaptively changing in order to achieve average bitrate which is constant over each Group of Picture (GOP). A relation between the bitrate, R and the QF, which is called Rate-QF (R-QF) model is derived in order to estimate the optimum QF of the current encoding frame for a given target bitrate, R. In some applications like video conferencing, real-time encoding and decoding with minimum delay is crucial, but, the ability to do real-time encoding/decoding is largely determined by the complexity of the encoder/decoder. As we all know that motion estimation process inside the encoder is the most time consuming stage. So, reducing the complexity of the motion estimation stage will certainly give one step closer to the real-time application. So, as a partial contribution toward realtime application, in the final phase of the research, a fast Motion Estimation (ME) strategy is designed and implemented. It is the combination of modified adaptive search plus semi-hierarchical way of motion estimation. The same strategy was implemented in both Dirac and H.264 in order to investigate its performance on different codecs. Together with this fast ME strategy, a method which is called partial cost function calculation in order to further reduce down the computational load of the cost function calculation was presented. The calculation is based upon the pre-defined set of patterns which were chosen in such a way that they have as much maximum coverage as possible over the whole block. In summary, this research work has contributed to the error-resilient transmission of compressed bitstreams of Dirac video encoder over a bandwidth limited error prone channel. In addition to this, the final phase of the research has partially contributed toward the real-time application of the Dirac video codec by implementing a fast motion estimation strategy together with partial cost function calculation idea.BBC R&D and Brunel University

Acoustic and Respiratory Characteristics of Infant Vocalization

The purpose of this dissertation was to explore vibratory regime of infant phonation. The first study examined 1) differences in overall levels of acoustic and respiratory variables between different regimes and 2) differences in relationships between the acoustic and respiratory variables among regimes. The second study examined 3) the acoustic and respiratory ranges of modal phonation with respect to other regimes and 4) the range of modal phonation among infants of different ages. Two datasets were used in the study. Dataset I was acquired from eight infants of ages 8-18 months, and Dataset II from one infant of ages 4-6 months. Their vocalizations and respiratory movements were recorded during adult-interaction. Phonated segments were identified through waveform, spectrogram, and auditory inspection, and categorized into six mutually exclusive regimes (modal, pulse, loft, subharmonics, biphonation, and chaos). For each regime segment, the following measurements were made: fundamental frequency (F0), sound pressure level (SPL), expiratory slope, and relative lung volume at regime initiation. A series of linear mixed-effects model analysis and analysis of variance revealed differences in mean F0 between regimes, mean SPL, and mean. Correlations between the acoustic and respiratory variables differed among regimes, indicating their relationships were regime-dependent. The most revealing findings were that regime categories readily distributed into different regions of the intensity-frequency space, and that F0 ranges of modal regime tended to decrease with increasing age. In addition to modal, pulse, and loft distributing around the mid, low, and high intensity-frequency regions, respectively, biphonation and subharmonics were found between modal and loft ranges. The upper end of F0 range for pulse was much higher in infants compared to adults, however, biphonation and subharmonics rarely occurred between pulse and modal ranges. A range of modal F0 was about 500 Hz for the young infant in the vocal expansion stage, and about 200 Hz for older infants in the (post-)canonical stage. Although the results are tentative, this finding suggests that F0 variability decreases with age and phonation becomes more restricted to a lower end of an F0 range