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Discharge regularity in the turtle posterior crista: comparisons between experiment and theory

JOURNAL OF NEUROPHYSIOLOGY 2013年第12期110卷 2830-2848页

作者： Goldberg, Jay M. Holt, Joseph C. Univ Chicago Dept Pharmacol & Physiol Sci Chicago IL 60637 USA

Intra-axonal recordings were made from bouton fibers near their termination in the turtle posterior crista. Spike discharge, miniature excitatory postsynaptic potentials (mEPSPs), and afterhyperpolarizations (AHPs) were monitored during resting activity in both regularly and irregularly discharging units. Quantal size (qsize) and quantal rate (qrate) were estimated by shot-noise theory. Theoretically, the ratio, sigma(V)/(d mu(V)/dt), between synaptic noise (sigma(V)) and the slope of the mean voltage trajectory (d mu(V)/dt) near threshold crossing should determine discharge regularity. AHPs are deeper and more prolonged in regular units;as a result, d mu(V)/dt is larger, the more regular the discharge. The qsize is larger and qrate smaller in irregular units;these oppositely directed trends lead to little variation in sigma(V) with discharge regularity. Of the two variables, d mu(V)/dt is much more influential than the nearly constant sigma(V) in determining regularity. Sinusoidal canal-duct indentations at 0.3 Hz led to modulations in spike discharge and synaptic voltage. Gain, the ratio between the amplitudes of the two modulations, and phase leads re indentation of both modulations are larger in irregular units. Gain variations parallel the sensitivity of the postsynaptic spike encoder, the set of conductances that converts synaptic input into spike discharge. Phase variations reflect both synaptic inputs to the encoder and postsynaptic processes. Experimental data were interpreted using a stochastic integrate-and-fire model. Advantages of an irregular discharge include an enhanced encoder gain and the prevention of nonlinear phase locking. Regular and irregular units are more efficient, respectively, in the encoding of low-and high-frequency head rotations, respectively.

关键词： discharge regularity miniature excitatory postsynaptic potentials afterhyperpolarizations integrate-and-fire model coding efficiency

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Performance Comparison of H.265/MPEG-HEVC, VP9, and H.264/MPEG-AVC Encoders

Performance Comparison of H.265/MPEG-HEVC, VP9, and H.264/MP...

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Picture coding Symposium (PCS)

作者： Grois, Dan Marpe, Detlev Mulayoff, Amit Itzhaky, Benaya Hadar, Ofer Fraunhofer Heinrich Hertz Inst HHI Image Proc Dept Berlin Germany Ben Gurion Univ Negev Commun Syst Engn Dept Beer Sheva Israel

ISBN: (纸本)9781479902941

This work presents a performance comparison of the two latest video coding standards H.264/MPEG-AVC and H.265/MPEG-HEVC (High-efficiency Video coding) as well as the recently published proprietary video coding scheme VP9. According to the experimental results, which were obtained for a whole test set of video sequences by using similar encoding configurations for all three examined representative encoders, H.265/MPEG-HEVC provides significant average bit-rate savings of 43.3% and 39.3% relative to VP9 and H.264/MPEG-AVC, respectively. As a particular aspect of the conducted experiments, it turned out that the VP9 encoder produces an average bit-rate overhead of 8.4% at the same objective quality, when compared to an open H.264/MPEG-AVC encoder implementation - the x264 encoder. On the other hand, the typical encoding times of the VP9 encoder are more than 100 times higher than those measured for the x264 encoder. When compared to the full-fledged H.265/MPEG-HEVC reference software encoder implementation, the VP9 encoding times are lower by a factor of 7.35, on average.

关键词： H.265 High efficiency Video coding (HEVC) VP9 H.264 AVC x264 video coding coding efficiency

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Analyzing and Optimizing Video Quality in the New H.265 (HEVC) Standard

Analyzing and Optimizing Video Quality in the New H.265 (HEV...

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SMPTE Technical Conference

作者： Advait Mogre Bhupender Kumar Shekhar Madnani Muneesh Sharma Shailesh Kumar Interra Systems 1601 S. De Anza Blvd. Suite 212 Cupertino CA 95014 USA

ISBN: (纸本)9781629938370

The emerging H.265 High efficiency Video coding (HEVC) standard for video compression is geared towards providing high quality / high resolution video at low to moderate bit rates; thus providing a significant increase in compression efficiency over existing standards like H.262/263/264. As is typically the case, increased compression results in decreased coding redundancy. Hence from a video quality perspective, of interest would be the nature of potential coding artifacts as well as the profile of video failures or dropouts arising due to uncorrected coding errors. In the latter case, the occurrence of these uncorrectable errors would depend upon external factors like the channel SNR or Eb/No profile, coupled with the source coding efficiency (or redundancy); the latter being governed by the opposing constraints of picture quality versus allowable bit rate or channel bandwidth. — The initial portion of this work is focused on dropout profiles due to randomly occurring bitstream errors. The geometries of the manifested dropout regions are quite noticeable as compared to those observed in traditional slice based video syntax for the same content, under a similar random error profile. This uniqueness impacts the spatial dropout detection algorithms to be used. — In the latter part of this work, video quality for a variety of content applications (like sports, news/talk shows, animation, etc…) and under varying encoder parameter profiles is monitored. The goal is to optimize the HEVC encoding parameters such as Transform Unit size, coding Unit size and Maximum Partition Depth for video quality, for each chosen content application.

关键词： H.265 HEVC AVC MPEG2 coding efficiency Dropout profiles Encoding parameters PSNR Blockiness Peak signal-to-noise ratio Automatic voltage control High efficiency video coding Videotapes Bit rate block effect Video compression dropouts

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Comparison of Bandpass ΣΔ Modulator coding efficiency With a Periodic Signal Model

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IEEE TRANSACTIONS ON CIRCUITS AND SYSTEMS I-REGULAR PAPERS 2008年第11期55卷 3763-3775页

作者： Johnson, Thomas Stapleton, Shawn P. PulseWave RF Austin TX 78746 USA Simon Fraser Univ Sch Engn Burnaby BC V5A 1S6 Canada

Maximizing coding efficiency is important in applications where bandpass Sigma Delta modulation is used as a source encoder to synthesize a two-level pulse train in RF class-D amplifiers. A periodic pulse-train model is developed to mimic the encoding of a bandpass Sigma Delta modulator for sinusoidal source signals, and it is shown that the coding efficiency of both the model and the modulator vary similarly with changes in carrier over-sample ratio. The relationship between-coding efficiency and carrier over-sample ratio is not monotonic and has significant dips at certain ratios. The predictions of the model are compared with simulation results for a fourth-order bandpass modulator. The results show that coding efficiency is low in a modulator design where the input frequency is one-fourth the sample rate (f(s)) and can be increased by as much as 15% by selecting a slightly lower over-sample ratio such-as (3/10)f(s).

关键词： Bandpass sigma-delta (Sigma Delta) modulation class-D amplifier coding efficiency RF power amplifier

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Dynamic threshold-based keyframe detection and its application in rate control

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IET IMAGE PROCESSING 2012年第7期6卷 986-995页

作者： Yao, W. Li, Z. Rahardja, S. Inst Infocomm Res Signal Proc Dept Singapore Singapore

This study proposes a new dynamic threshold model to detect keyframes for the coding of a video sequence. The proposed detection threshold is content adaptive which dynamically updates its value at each frame by taking into consideration both the statistical properties of the video sequence and the resolution as well as the quantisation parameters. The content variation metric used in the proposed detection method utilises the information that is already generated by the encoder during the encoding process and thus it makes the detection process fast. By applying the proposed scheme to rate control, the sizes of group of pictures are now adapted to the video content and it removes the temporal redundancy among different frames better, which transforms to the improvements on coding efficiency. The experimental results have shown that the proposed method achieves peak signal-to-noise ratio (PSNR) improvement.

关键词： image resolution statistical analysis temporal redundancy encoding process dynamic threshold model dynamic threshold-based keyframe detection coding efficiency Image and video coding rate control quantisation parameters quantisation (signal) encoder video coding image sequences peak signal-to-noise video resolution Video signal processing detection process content variation metric statistical properties video sequence coding PSNR Other topics in statistics

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Design of a context-adaptive variable length encoder for real-time video compression on reconfigurable platforms

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IET IMAGE PROCESSING 2012年第4期6卷 301-308页

作者： Licciardo, G. D. Albanese, L. Freda Univ Salerno Dept Elect & Informat Engn DIEII I-84084 Salerno Italy

In this study, a new context-adaptive variable length-coding encoder architecture is proposed particularly aimed to be implemented with field programmable logics (FPL) like FPGAs. The design implements different approaches in order to minimise the area cost as well as to speed up the coding efficiency, which allows real-time compression of 1080 p video streams coded in YCbCr 4:2:0 format. Priority cascading logics have been implemented in order to increase the parallelisation degree of the pre-coding stage, thus favouring the limitation of the number of clock cycles needed for the extraction of symbols from the input data, whereas the employment of the arithmetic table elimination technique has allowed a large-area reduction of the encoder thanks to the elimination of 18 of the 38 tables needed for the encoding stage. The design achieves real time elaboration with an operation frequency of 63 MHz and occupies 2200 look-up table (LUT)s when implemented on a low-cost, low-end XILINX Spartan 3 FPGA, thus overcoming the most recent FPL implementation and making this encoder quite comparable both in terms of area and speed with some recently proposed ASIC implementations, so that it turns out to be a valid alternative also for application specific implementations.

关键词： precoding parallelisation degree field programmable logics look-up table reconfigurable platform data compression table lookup variable length codes field programmable gate arrays FPL implementation Xilinx Spartan 3 real-time video compression coding efficiency priority cascading logics Image and video coding precoding stage arithmetic table elimination technique low-end XILINX Spartan 3 FPGA Logic circuits Computer architecture video coding Logic and switching circuits clocks reconfigurable architectures YCbCr 4:2:0 format context-adaptive variable length-coding encoder architecture Video signal processing video streaming length-coding encoder architecture symbols extraction clock cycle ASIC implementation

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Memory Efficient Set Partitioning in Hierarchical Tree (MESH) for Wavelet Image Compression

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IEICE TRANSACTIONS ON COMMUNICATIONS 2012年第9期E95B卷 2906-2913页

作者： Ghani, Farid Kader, Abdul Khan, Ekram Ahmad, Badlishah Univ Malaysia Perlis Sch Comp & Commun Engn Kuala Perlis 02000 Perlis Malaysia Aligarh Muslim Univ Dept Elect Engn Aligarh 202002 Uttar Pradesh India

This paper presents a memory efficient version of set partitioning in hierarchical tree (SPIHT). The proposed coder called Memory Efficient SPIHT (MESH) uses a single re-usable list instead of three continuously growing linked lists as in conventional SPIHT. The list is re-initialized at the beginning of each bit-plane (coding pass) and is exhausted within the same bit-plane. Another feature of the proposed coder is that it uses a single pass for each bit-plane by merging the sorting and refinement passes of the conventional version of SPIHT. The performance of the proposed coder is measured in terms of coding efficiency, and the worst case dynamic memory requirements due to the list entries in each bit-plane. Performance comparison with SPIHT shows that the proposed coder reduces the dynamic memory requirement by about 50-70% compared to the SPIHT while retaining its coding efficiency.

关键词： coding efficiency image coding reduced memory SPIHT wavelet transform

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Perceptual Video Compression: A Survey

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IEEE JOURNAL OF SELECTED TOPICS IN SIGNAL PROCESSING 2012年第6期6卷 684-697页

作者： Lee, Jong-Seok Ebrahimi, Touradj Yonsei Univ Sch Integrated Technol Inchon 406840 South Korea Ecole Polytech Fed Lausanne Inst Elect Engn Multimedia Signal Proc Grp CH-1015 Lausanne Switzerland

With the advances in understanding perceptual properties of the human visual system and constructing their computational models, efforts toward incorporating human perceptual mechanisms in video compression to achieve maximal perceptual quality have received great attention. This paper thoroughly reviews the recent advances of perceptual video compression mainly in terms of the three major components, namely, perceptual model definition, implementation of coding, and performance evaluation. Furthermore, open research issues and challenges are discussed in order to provide perspectives for future research trends.

关键词： coding efficiency focus of attention human visual system perceptual video compression quality of experience (QoE) region of interest visual perception

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Video compression based on frequency sensitivity

Video compression based on frequency sensitivity

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Conference on Satellite Data Compression, Communications, and Processing VIII

作者： Seo, Guiwon Youn, Sungwook Lee, Chulhee Yonsei Univ Dept Elect & Elect Engn Seoul 120749 South Korea

ISBN: (纸本)9780819492319

In this paper, we investigate the frequency sensitivity of the human visual system. The human visual system reacts differently at different frequencies. Based on this observation, we used different quantization steps for different frequency components to explore the possibility of improving coding efficiency while maintaining perceptual video quality. In other words, small quantization steps were used for sensitive frequency components while large quantization steps were used for less sensitive frequency components.

关键词： video compression frequency sensitivity HVS coding efficiency perceptual video quality

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AN EFFICIENT SURVEILLANCE coding METHOD BASED ON A TIMELY AND BIT-SAVING BACKGROUND UPDATING MODEL

AN EFFICIENT SURVEILLANCE CODING METHOD BASED ON A TIMELY AN...

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IEEE Visual Communications and Image Processing (VCIP)

作者： Chen, Wei Zhang, Xianguo Tian, Yonghong Huang, Tiejun Peking Univ Natl Engn Lab Video Technol Beijing 100871 Peoples R China

ISBN: (纸本)9781467344050

(1)Background modeling is an important pre-processing step for object detection in surveillance video analysis systems. Recently, it has been proved to be useful for high-efficiency surveillance video coding. In existing works, the modeling background frame often needs to be high-quality encoded so as to achieve a large bit-rate saving. However, the high-quality background frame requires lots of bits in the code stream, so it is infeasible to update the background frame too frequently. Therefore, a better bit-allocation method is desirable to facilitate in-time background updating and bit-saving background coding. In this paper, we firstly build up a background updating model from a detailed analysis of results on surveillance video. Following this, we propose a bit-saving and quality-maintaining background frame coding method. In our method, the background frame can be updated more timely, consequently leading to the better coding efficiency. Experimental results show that our method can achieve more than 15% bit-rate decrease compared with three state-of-art methods.

关键词： surveillance video coding bit-saving background updating bit-allocation coding efficiency

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