Motion‐Compensated Transform Coding

Interframe Hybrid Transform/dpcm Coders Encode Television Signals by Taking a Spatial Transform of a Block of Picture Elements in a Frame and Predictively Coding the Resulting Coefficients using the Corresponding Coefficients of the Spatial Block at the Same Location in the Previous Frame. These Coders Can Be Made More Efficient for Scenes Containing Objects in Translational Motion by First Estimating the Translational Displacement of Objects and Then using Coefficients of a Spatially Displaced Block in the Previous Frame for Prediction. This Paper Presents Simulation Results for Such Motion‐compensated Transform Coders using Two Algorithms for Estimating Displacements. the First Algorithm, Which is Developed in a Companion Paper, Recursively Estimates the Displacements from the Previously Transmitted Transform Coefficients, Thereby Eliminating the Need to Transmit the Displacement Estimates. the Second Algorithm, Due to Limb and Murphy, Estimates Displacements by Taking Ratios of Accumulated Frame Difference and Spatial Difference Signals in a Block. in This Scheme, the Displacement Estimates Are Transmitted to the Receiver. Computer Simulations on Two Typical Real‐life Sequences of Frames Show that Motion‐compensated Coefficient Prediction Results in Coder Bit Rates that Are 20 to 40 Percent Lower Than Conventional Interframe Transform Coders using Frame Difference of Coefficients. Comparisons of Bit Rates for Approximately the Same Picture Quality Show that the Two Methods of Displacement Estimation Are Quite Similar in Performance with a Slight Preference for the Scheme with Recursive Displacement Estimation. © 1979 the Bell System Technical Journa

The Effect of Channel Errors in the Differential Pulse-Code-Modulation Transmission of Sampled Imagery

This Paper Presents an Analysis, Simulation, and Discussion of the Effects of Communication Errors on Four-Bit Differential Pulse-Code Modulation (DPCM) Sampled Imagery. Simulations Are Presented that Describe the Effects of Inserting Periodic PCM Updates in Order to Correct Communication Errors in the DPCM Transmission of Photographic Scenes that Have Been Scanned and Sampled at the Nyquist Rate. Copyright © 1971 by the Institute of Electrical and Electronics Engineers, Inc

Academic freedom in Europe: time for a Magna Charta?

This paper is a preliminary attempt to establish a working definition of academic freedom for the European Union states. The paper details why such a definition is required for the European Union and then examines some of the difficulties of defining academic freedom. By drawing upon experience of the legal difficulties beset by the concept in the USA and building on previous analyses of constitutional and legislative protection for academic freedom, and of legal regulations concerning institutional governance and academic tenure, a working definition of academic freedom is then derived. The resultant definition which, it is suggested, could form the basis for a European Magna Charta Libertatis Academicae, goes beyond traditional discussions of academic freedom by specifying not only the rights inherent in the concept but also its accompanying duties, necessary limitations and safeguards. The paper concludes with proposals for how the definition might be tested and carried forward

Infrared Behaviour of the Gluon Propagator: Confining or Confined?

The possible infrared behaviour of the gluon propagator is studied analytically, using the Schwinger-Dyson equations, in both the axial and the Landau gauge. The possibility of a gluon propagator less singular than $1/k^{2}$ when $k^{2} \rightarrow 0$ is investigated and found to be inconsistent, despite claims to the contrary, whereas an infrared enhanced one is consistent. The implications for confinement are discussed.Comment: 20 pages, latex, 2 figure

Structure at Work: Organizational Forms and the Division of Labor in U.S. Wineries

We show how organizational forms shape job structures, specifically the variety and types of jobs employees hold, extending previous research on job structures in four ways. First, the social codes associated with wineries' generalist and specialist forms constrain the number of jobs and functional areas delineated by job titles. Second, form-based constraints are weakened by institutional rules that impose categorical distinctions on organizations. Third, these constraints are stronger when there is more consensus around forms. Fourth, these constraints are contingent on the legitimacy and resources of organizations of varying ages and sizes

Linear Resolution Enhancement

This Paper Describes the Tradeoff between Resolution and Noise that Exists in Imaging Systems that Employ Computer Compensation of the Input Point Spread Function. Emphasis is Placed Upon Systems Having Circularly Symmetric Blur Degradation, Particularly the Airy and the Gaussian Spots. the Paper Describes How Optimum Deconvolutional Processing Arrays Can Be Efficiently Computed. Quantitative Results Are Given for Airy and Gaussian Spot Compensation under a Variety of Image Sampling Raster Dimensions and Patterns. © 1976 Academic Press, Inc

Transform Domain Motion Estimation

This Paper Introduces an Algorithm for Estimating the Displacement of Moving Objects in a Television Scene from Spatial Transform Coefficients of Successive Frames. the Algorithm Works Recursively in Such a Way that the Displacement Estimates Are Updated from Coefficient to Coefficient. a Promising Application of This Algorithm is in Motion‐compensated Interframe Hybrid Transform‐dpcm Image Coding. We Give a Statistical Analysis of the Transform Domain Displacement Estimation Algorithm and Prove its Convergence under Certain Realistic Conditions. an Analytical Derivation is Presented that Gives Sufficient Conditions for the Rate of Convergence of the Algorithm to Be Independent of the Transform Type. This Result is Supported by a Number of Simulation Examples using Hadamard, Haar, and Slant Transforms. We Also Describe an Extension of the Algorithm that Adaptively Updates Displacement Estimation According to the Local Features of the Moving Objects. Simulation Results Demonstrate that the Adaptive Displacement Estimation Algorithm Has Good Convergence Properties in Estimating Displacement Even for Very Noisy Images. © 1979 the Bell System Technical Journa

Algorithms for rewriting aggregate queries using views

Queries involving aggregation are typical in database applications. One of the main ideas to optimize the execution of an aggregate query is to reuse results of previously answered queries. This leads to the problem of rewriting aggregate queries using views. Due to a lack of theory, algorithms for this problem were rather ad-hoc. They were sound, but were not proven to be complete. Recently we have given syntactic characterizations for the equivalence of aggregate queries and applied them to decide when there exist rewritings. However, these decision procedures do not lend themselves immediately to an implementation. In this paper, we present practical algorithms for rewriting queries with count and sum. Our algorithms are sound. They are also complete for important cases. Our techniques can be used to improve well-known procedures for rewriting non-aggregate queries. These procedures can then be adapted to obtain algorithms for rewriting queries with min and max. The algorithms presented are a basis for realizing optimizers that rewrite queries using views