John C. Beatty

Color gamut mapping and the printing of digital color images

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.

Local Control of Bias and Tension in Beta-splines

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.

An experimental comparison of RGB, YIQ, LAB, HSV, and opponent color models

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 users 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.

Using color dimensions to display data dimensions

One of the advantages of computer graphics is that it enables an unprecedented degree of control over color. Since color vision is three-dimensional, this provides three additional perceptual dimensions that may be used in addition to the two spatial dimensions available on a flat display to present multidimensional data. This research probes the usefulness of color in enabling human observers to perceive clusters of points in a multidimensional space. Comparing the resolution of clusters in color and in space shows that color is an effective extension of space for conveying information about data dimensions. However, the perceptual space defined by color and space is not homogeneous and resolution is poor in a few specific directions. For this reason, the use of multiple views is advocated whenever color is used as a tool in exploratory data analysis.

The message is the medium: Multiprocess structuring of an interactive paint program

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. The Thoth operating system was used to experiment with such an anthropomorphic design. Thoth provides a hospitable environment in which to investigate the distribution of algorithms between software and microprogrammed hardware processes, the performance and responsiveness of a multiple-process interactive program, and experimental user interfaces using an Ikonas 3000 frame buffer. The paint program consists of processes which handle the graphics tablet, track an iconic cursor, paint a selection of brushes, fill regions of the image, draw lines, and implement the user interface. Some processes have been implemented both in software and microcode.

Experimental comparison of splines using the shape-matching paradigm

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 C2 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

A Computerized Editor of Benesh Movement Notation

Notation plays a very important role in todays society. It acts as a communication medium between inventors and those who will implement their ideas. Without notation our knowledge of the past and present would be limited by our memory and prone to errors in oral transmission. Although we take for granted the existence of a suitable notation in almost all fields of human study, this is not true in the field of human movement. For example, in Western theatrical dance, no adequate means to record masterpieces existed until the twentieth century and thus most works from the past have been lost. In response to the literacy problem in dance, a number of systems have been developed in the past five centuries to record human movement, but most of these have failed to be practical under rigorous working conditions. Only a few have attracted substantial professional interest. The difficulty is that a dance notation must capture on paper a precise record, at

On the relationship between LL(1) and LR(1) grammars

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).

Raster Graphics and Color

Abstract For the past decade low cost computer graphics terminals have consisted almost exclusively of direct view storage tube (DVST) devices. Recently, however, a new variety of terminal based on “raster TV technology” has emerged which is competitive with storage tubes in price and readily supports variable intensity and color. We summarize the basic organization of raster terminals so as to indicate their capabilities, discuss their advantages and disadvantages, and illustrate some of their uses in statistics and elsewhere. Because color is almost universally available on these terminals, we also discuss some elementary principles of color perception and use. An understanding of this material will help the data analyst present data effectively.

An interactive documentation system

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.