There are a variety of spline formulations for specifying smooth curves.In theory, many of these are equivalent in terms of the families of curves that can be obtained.In practice, each formulation encourages the implementation of certain styles of interaction in a curve editor and discourages other styles.This paper presents the design, implementation, and analysis of four experiments to illustrate a general shape-matching paradigm for studying interactive curve manipulation.We introduce the new shape-matching paradigm as a methodology for analyzing user performance.We then report on a series of studies that employ this paradigm to explore the relationship between a commonly used interaction style for curve design and various spline formulations, Controlled experiments were performed to test the hypothesis that the style of interaction implicit in the movement of single design points will influence the ease with which curve manipulation can be performed using a variety of spline formulations.Although such interactions are of a simple form, the experience gained in these studies has already enabled us to undertake more extensive experiments with more sophisticated interaction styles.The specific experiments reported here compare five formulations of cubic splines (B-splines, B6zier splines, Catmull-Rom splines, and two versions of interpolating splines with C 2 continuity), Data from the experiments show that, for the particular shape-matching tasks investigated, there is a significant performance difference among the five formulations.The B-spline formulation was best for the task, both in terms of match quality and in terms of the time required to Financial support for this research was provided by the

Principles and techniques useful for calibrated color reproduction are defined. These results are derived from a project to take digital images designed on a variety of different color monitors and accurately reproduce them in a journal using digital offset printing. Most of the images printed were reproduced without access to the image as viewed in its original form; the color specification was derived entirely from calorimetric specification. The techniques described here are not specific to offset printing and can be applied equally well to other digital color devices. The reproduction system described is calibrated using CIE tristimulus values. An image is represented as a set of three-dimensional points, and the color output device as a three-dimensional solid surrounding the set of all reproducible colors for that device, called its gamut . The shapes of the monitor and the printer gamuts are very different, so it is necessary to transform the image points to fit into the destination gamut, a process we call gamut mapping . This paper describes the principles that control gamut mapping. Included also are some details on monitor and printer calibration, and a brief description of how digital halftone screens for offset printing are prepared.

The increasing availability of affordable color raster graphics displays has made it important to develop a better understanding of how color can be used effectively in an interactive environment. Most contemporary graphics displays offer a choice of some 16 million colors; the user's problem is to find the right color. Folklore has it that the RGB color space arising naturally from color display hardware is user-hostile and that other color models such as the HSV scheme are preferable. Until now there has been virtually no experimental evidence addressing this point. We describe a color matching experiment in which subjects used one of two tablet-based input techniques, interfaced through one of five color models, to interactively match target colors displayed on a CRT. The data collected show small but significant differences between models in the ability of subjects to match the five target colors used in this experiment. Subjects using the RGB color model matched quickly but inaccurately compared with those using the other models. The largest speed difference occurred during the early convergence phase of matching. Users of the HSV color model were the slowest in this experiment, both during the convergence phase and in total time to match, but were relatively accurate. There was less variation in performance during the second refinement phase of a match than during the convergence phase. Two-dimensional use of the tablet resulted in faster but less accurate performance than did strictly one-dimensional usage. Significant learning occurred for users of the Opponent, YIQ, LAB, and HSV color models, and not for users of the RGB color model.

The Beta-spline introduced recently by Barsky is a generalization of the uniform cubic B-spline: parametric discontinuities are introduced in such a way as to preserve continuity of the unit tangent and curvature vectors at joints (geometric continuity) while providing bias and tension parameters, independent of the position of control vertices, by which the shape of a curve or surface can be manipulated. Using a restricted form of quintic Hermite interpolation, it is possible to allow distinct bias and tension parameters at each joint without destroying geometric continuity. This provides a new means of obtaining local control of bias and tension in piecewise polynomial curves and surfaces.

This paper describes an interactive computerized editor for Benesh Movement Notation that aids in the preparation of dance scores on a medium resolution colour display. Benesh Movement Notation is a two-dimensional system for recording human movement in three dimensions of space which has been successfully used in the preparation of scores for a wide repertoire of dances. The preparation and revision of Benesh scores is a lengthy and error-prone process which interactive editing techniques can greatly facilitate. We describe the current state and future extensions of a prototype editing system in which all user interaction is based on a menu-driven scheme using a graphics tablet. Extensive visual cues including iconic trackers and semantic information are provided at all times. Both user and system initiated dialogues are supported. This system has served as a testbed for a variety of man-machine interaction studies, allowing us to transfer the wealth of experience with interactive text editing to a related task: the preparation of dance scores. The project has given us a better understanding of the issues involved in implementing an effective user-interface.

TensionThe Beta-spline introduced recently by Barsky is a generalization of the uniform cubic B-spline: parametric discontinuities are introduced in such a way as to preserve continuity of the unit tangent and curvature vectors at joints (geometric continuity) while providing bias and tension parameters, independent of the position of control vertices, by which the shape of a curve or surface can be manipulated.Using a restricted form of quintic Hermite interpolation, it is possible to allow distinct bias and tension parameters at each joint without destroying geometric continuity.This provides a new means of obtaining local control of bias and tension in piecewise polynomial curves and surfaces.

An innovative design for an interactive paint program has been developed based on multiple processes and message passing. Traditional paint programs combine interrupt-driven support of a graphical input device, such as a mouse or tablet, with the coloring of pixels in a raster display. We advocate a different design methodology which is illustrated in our implementation. The multiple processes and message passing primitives provided by some real-time operating systems encourage the design of parallel-program architectures and anthropomorphic programming structures, analogous to artist procedures and the metaphors of Smalltalk.

It is shown that every p-reduced LL(I) grammar is LALR(I) and, as a corollary, that every A-free LL(I) grammar is SLR(I) A partial converse to this result is also demonstrated: If there is at most one marked rule m the basis of every state set in the canonical collection of sets of LR(k) items for a grammar G in which S i~ S-/ts impossible, then G ~s LL(k).

Most chronic users of time sharing computer systems are familiar with programs that allow the creation and manipulation of text files. Less often they have at their disposal programs that will format the document described by a text file, generating output such as a typist might produce. Rarely is there any mechanism by which graphics can be integrated with text. Lawrence Livermore Laboratory has a powerful, flexible and interactive computer-based documentation system that will format a source document description according to user specifications and incorporate illustrations to produce online documents, offset reproduction masters, 35mm color slides, movie titles, or viewgraphs. The flexibility of the system is greatly enhanced by the use of a device independent graphics library. Text may be plotted using the hardware characters specific to a device (when possible), or may be drawn as Hershey characters or polygonally outlined symbols. Illustrations may be defined in a simple 2d graphics language, and graphical output from application programs may also be incorporated directly into a document.

The classical pumping lemma [BP&S] and Ogden's lemma [Og] are among the most powerful tools we possess for proving that languages are not context-free. Hence one goal of recent research has been to obtain analogous theorems for subclasses of the context-free languages. We establish here a property of LL(k) derivation trees which is analogous to the left part property for strict deterministic grammars[H&H]. We show that our property characterizes LL(k) grammars and use it to establish two iteration theorems for the LL languages. These theorems, in turn, enable us to prove simply and rigorously that a variety of LR languages are not LL. In particular, the “dangling” Algol 60 IF-THEN-ELSE construct allowed in Pascal and PL/1 cannot be generated by an LL(k) grammar.