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Contrast conservation in human vision

VISION RESEARCH 2003年第25期43卷 2637-2648页

作者： Fiser, J Bex, PJ Makous, W Univ Rochester Ctr Visual Sci Rochester NY 14627 USA UCL Inst Ophthalmol London EC1V 9EL England

Visual experience. which is defined by brief saccadic sampling of complex scenes at high contrast, has typically been studied with static gratings at threshold contrast. To investigate how suprathreshold visual processing is related to threshold vision, we tested the temporal integration of contrast in the presence of large, sudden changes in the stimuli such occur during saccades under natural conditions. We observed completely different effects under threshold and suprathreshold viewing conditions. The threshold contrast of successively presented gratings that were either perpendicularly oriented or of inverted phase showed probability summation, implying no detectable interaction between independent visual detectors. However, at suprathreshold levels we found complete algebraic summation of contrast for stimuli longer than 53 ms. The same results were obtained during sudden changes between random noise patterns and between natural scenes. These results cannot be explained by traditional contrast gain-control mechanisms or the effect of contrast constancy. Rather, at suprathreshold levels, the visual system seems to conserve the contrast information from recently viewed images, perhaps for the efficient assessment of the contrast of the visual scene while the eye saccades from place to place. (C) 2003 Elsevier Ltd. All rights reserved.

关键词： suprathreshold dynamic contrast discrimination channel model natural scene coding efficiency

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Local contrast in natural images: normalisation and coding efficiency

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PERCEPTION 2000年第9期29卷 1041-1055页

作者： Brady, N Field, DJ Natl Univ Ireland Univ Coll Dublin Dept Psychol Dublin 4 Ireland Cornell Univ Dept Psychol Ithaca NY 14853 USA

The visual system employs a gain control mechanism in the cortical coding of contrast whereby the response of each cell is normalised by the integrated activity of neighbouring cells. While restricted in space, the normalisation pool is broadly tuned for spatial frequency and orientation, so that a cell's response is adapted by stimuli which fall outside its 'classical' receptive field. Various functions have been attributed to divisive gain control: in this paper we consider whether this output nonlinearity serves to increase the information carrying capacity of the neural code. 46 natural scenes were analysed with the use of oriented, frequency-tuned filters whose bandwidths were chosen to match those of mammalian striate cortical cells. The images were logarithmically transformed so that the filters responded to a luminance ratio or contrast. In the first study, the response of each filter was calibrated relative to its response to a grating stimulus, and local image contrast was expressed in terms of the familiar Michelson metric. We found that the distribution of contrasts in natural images is highly kurtotic, peaking at low values and having a long exponential tail. There is considerable variability in local contrast, both within and between images. In the second study we compared the distribution of response activity before and after implementing contrast normalisation, and noted two major changes. Response variability, both within and between scenes, is reduced by normalisation, and the entropy of the response distribution is increased after normalisation, indicating a more efficient transfer of information.

关键词： .gain receptive neighbouring OUTPUT spatial frequency tuned contrasts Natural Scenes luminance natural images image contrast striate filters calibrated cortical cells Local contrast coding efficiency normalisation pool

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Wavelet packet algorithm for quadtree-based embedded image coding

Wavelet packet algorithm for quadtree-based embedded image c...

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IEEE International Conference on Acoustics, Speech, and Signal Processing

作者： Uto, T Ikehara, M Okuda, M Keio Univ Fac Sci & Technol Tokyo 108 Japan

ISBN: (纸本)0780374029

Wavelet packets represent an elegant generalization of the wavelet transform, capable of providing arbitrary frequency resolution to meet a signal's spectral behaviors. Recent research advances have shown that wavelet-based image compression techniques offer several advantages over traditional techniques in terms of progressive transmission capability and compression efficiency. The embedded compression techniques - tree-structured coding techniques, such as embedded zerotree wavelet (EZW) and set partitioning in hierarchical trees (SPIHT), and quadtree-structured coding techniques, such as wavelet quadtree (WQT), multigrid embedded (MGE) and EZW based on intraband partitioning (EZW-IP), - demonstrate the competitive performance of wavelet based compression schemes. This paper describes the wavelet packet algorithm which makes it suited to subsequent quadtree-based embedded image coders, such as EZW-IP. In our technique, the hierarchical sums of maximum magnitude of each quadtree node role as the decomposition criterion. The simulation results for various images show that the proposed algorithm gives a better coding efficiency than the octave-band decomposition.

关键词： quadtrees image coding data compression wavelet transforms transform coding set theory wavelet packet algorithm quadtree-based embedded image coding wavelet transform frequency resolution wavelet-based image compression progressive transmission compression efficiency embedded compression techniques tree-structured coding embedded zerotree wavelet coding set partitioning in hierarchical trees SPIHT quadtree-structured coding multigrid embedded coding intraband partitioning EZW-IP simulation results coding efficiency octave-band decomposition

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Connected operators based on reconstruction process for size and motion simplification

Connected operators based on reconstruction process for size...

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IEEE International Conference on Acoustics, Speech, and Signal Processing

作者： Salembier, P Ruiz, J Univ Politecn Cataluna Barcelona Spain

ISBN: (纸本)0780374029

This paper deals with connected operators based on reconstruction process. Connected operators are filtering tools that act on the connected components of the space where the image is constant, the so-called "flat zones". Intuitively, connected operators can remove boundaries between flat zones but cannot add new boundaries nor shift existing contours. After reviewing the filtering strategy, new operators are proposed to perform size and motion simplification. In the case of size simplification, the proposed approach allows a better preservation the contrast of maxima or minima that have not been totally simplified by the filtering process. In the case of motion simplification, two applications are presented: motion detection for maxima/minima and sequence simplification to improve the coding efficiency of standard encoders.

关键词： mathematical operators data compression median filters image reconstruction motion estimation video coding connected operators reconstruction process filtering tools flat zones size simplification motion simplification maxima/minima motion detection coding efficiency standard encoders video coding

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Modifications on morphology-based image coding

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ELECTRONICS LETTERS 2001年第7期37卷 421-422页

作者： Cai, ZH Subramanian, KR Cheng, TH Nanyang Technol Univ Sch EEE Singapore 639798 Singapore

An extension uf morphology-based image coding is presented. Tv achieve better coding efficiency neighbour coefficients are included into the significance m;ip predictor and different subband quantisers are employed to achieve the optimal quantiser fur each subband in a rare-distortion sense, Experimental results show. that about 0.4-0.7dB peak signal-to-noise ratio pain can be obtained.

关键词： coding efficiency rate-distortion sense Image and video coding peak signal-to-noise ratio gain significance map predictor image coding optimal quantiser morphology-based image coding quantisation (signal) subband quantisers image morphing neighbour coefficients Computer vision and image processing techniques mathematical morphology

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Digital holographic memory using two-dimensional modulation code

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JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS BRIEF COMMUNICATIONS & REVIEW PAPERS 2001年第3B期40卷 1732-1736页

作者： Kume, T Yagi, S Imai, T Yamamoto, M NTT Cyber Space Labs Tokyo 1808585 Japan NTT Photon Labs Tokai Ibaraki 3191106 Japan

The degradation of reconstructed images from a digital holographic memory that uses highly sensitive strontium barium niobate as a recording medium was reduced using two-dimensional modulation codes that have low average intensity and high coding efficiency. The signal-to-noise ratios of the reconstructed images and hence the bit error rates of the data retrieved from the images were improved without reducing the coding efficiency.

关键词： digital holographic memory modulation code SBN signal-to-noise ratio bit error rate coding efficiency

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New window-switching criterion of audio compression

New window-switching criterion of audio compression

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4th IEEE Workshop on Multimedia Signal Processing (MMSP 01)

作者： Hou, ZR Dou, WB Dong, ZW Tsing Hua Univ Dept Elect Engn State Key Lab Microwave & Digital Commun Beijing 100084 Peoples R China

ISBN: (纸本)0780370252

The ERIC (Energy Ramp In Critical-band) criterion for window switching in perceptual audio coding Is proposed in this paper, This new criterion can distinguish the real burst signal from the stationary signals with high perceptual entropy effectively. Therefore, comparing with the Perceptual Entropy criterion used in the MPEG standard, the possibility of misjudgment of the window types is reduced by using the proposed criterion. It results in some improvements both on the audio quality and the coding efficiency.

关键词： entropy audio coding hearing audio compression window-switching criterion energy ramp critical-band perceptual audio coding burst signal perceptual entropy MPEG standard audio quality coding efficiency

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Factorisation for subclass of symmetric-antisymmetric multifilter banks and its application to image coding

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ELECTRONICS LETTERS 2000年第6期36卷 516-518页

作者： Gao, XQ Gan, L Zou, CR Southeast Univ Dept Radio Engn Nanjing 210096 Peoples R China

A complete and minimal factorisation is proposed for an important subclass of symmetric-antisymmetric multiwavelet filter banks (SAMFBs). Based on this factorisation, optimal SAMFBs are designed for image coding under an optimisation criterion. Experimental results show that the SAMFBs significantly outperform the traditional 9-7 wavelet in terms of coding efficiency, especially for hard-to-compress images.

关键词： optimisation symmetric-antisymmetric multifilter banks coding efficiency filtering theory Image and video coding data compression hard-to-compress images Filtering methods in signal processing Optimisation techniques optimisation criterion image coding minimal factorisation zerotree image coder multiwavelet filter banks Signal processing theory image coding application Computer vision and image processing techniques

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Identification of T-codes with minimal average synchronisation delay

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IEE PROCEEDINGS-COMPUTERS AND DIGITAL TECHNIQUES 2000年第4期147卷 237-240页

作者： Fong, ACM Higgie, GR Nanyang Technol Univ Sch Appl Sci Singapore 639798 Singapore Univ Auckland Dept Elect & Elect Engn Auckland 1 New Zealand

When T-codes are used to encode an information source most efficiently, their tendency towards self-synchronisation is among the strongest. The best T-codes achieve self-synchronisation within 1.5 characters following a lock loss. Attempts have been made to build databases of the best T-codes, These rely on the comparison of average synchronisation delay (ASD) values that have to be determined using complex algorithms. Criteria are proposed for selecting T-code sets that have intrinsically low ASD values. These criteria are derived from the underlying synchronisation process of T-codes based on the T-code construction algorithm. This latest contribution means that T-codes that are optimal, in terms of both coding efficiency and synchronisation performance, can be found for any given information source more easily compared to previous methods.

关键词： average synchronisation delay information source variable length codes encoding T-codes identification coding efficiency minimal average synchronisation delay Codes delays self-synchronisation Information theory

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Using scene-change detection and multiple-thread background memory for efficient video coding

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ELECTRONICS LETTERS 1999年第4期35卷 290-291页

作者： Zhang, K Kittler, J Univ Surrey Sch EEIT&M CVSSP Guildford GU2 5XH Surrey England

The use of background memory to improve coding efficiency has gained momentum recently due to the rapid decrease in the cost of memory chips. However, the associated computational costs still pose a problem for real time implementation. The authors propose a coding oriented scene-change detection algorithm and the use of multiple thread background memory to improve the coding efficiency of both scene-change frames and frames between two consecutive scene cuts. The experimental results show that the proposed scheme can improve the coding efficiency in both situations. The improvement is significant for scene-change frames.

关键词： coding efficiency Image and video coding Digital storage Video signal processing real time implementation scene-change frames digital storage real-time systems scene-change detection video coding multiple-thread background memory

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