Raster Display Research Articles

Standardizing the raster display for medical images using a fixed set of frame buffer primitives.

Two major difficulties associated with medical image processing are the diverse image formats that must be dealt with because of the differences in image sources and the number of incompatible display systems available for viewing images both before and after processing. We describe a very small set of primitives that need to be defined to utilize any raster display. When these primitives have been implemented for a particular device, then a standard set of image display programs can be compiled and images and the results of image processing can be displayed. The main purpose of this paper is to describe what a raster display looks like from the point of view of the programmer and to define the specific hardware and software data about the raster display that must be known in order to implement the small set of primitives.

A Raster Display Graphics Package for Education

We discuss in this article the need for a minimum suite of raster display routines, the design requirments for such a suite of routines, and the specifications for a package satisfying these design requirements. Finally, we outline our experience with the implementation and use of the resulting package in an educational environment. In the Appendix we give a detailed specification of the actual package we have developed and the user manual for that package.

Computer Animation of Storm Surge Predictions

With the proliferation of low‐cost graphics systems and small computers, high‐quality computer graphic representation of the modeling of geophysical flow is feasible. In this work, storm surge activity on Lake Erie is simulated by a Leendertse‐type model and the output from this model (water surface elevations) are pictured as three‐dimensional surfaces in an animated sequence. Four methods for constructing such images are surveyed: A wire‐frame plot on a line‐drawing device; a representation as a set of flat panels on a polygondrawing raster display; a smooth shaded rendering on a point‐addressable monochrome display; and a full‐color rendering with “highlights” on a larger color palette display. Each of these methods are assessed in terms of speed, economy, reliability, the ability to render all relevant scales of activity, and the ability to be comprehended readily and unambiguously.

Time-Resolved Laser Doppler Measurements in the Underexpanded Jet of a Model Gas-Blast Circuit Breaker under Arcing Conditions

A differential laser Doppler system has been used in conjunction with a self-triggered oscillographic raster display system for measuring particle concentrations and flow velocities in a model gas-blast circuit breaker. The flow velocities have been correlated with particle size to enable extrapolation to be made to determine the true plasma flow velocity. The results have been deconvoluted to take account of lateral movements of the arc column. The measurements have been taken with air as the host arcing medium and a flow through a 25-mm-diameter orifice sustained by an upstream pressure of about 7 bar (downstream pressure 1 bar). The arc was sustained by sinusoidal cuffents of peak values 3 and 8 kA and a frequency of 85 Hz. These two currents corresponded to conditions when the model circuit breaker successfully and unsuccessfully interrupted the arc-sustaining current, respectively. The results show that in the case of the 8-kA arc, the flow pattern is severely distorted from that under nonarcing conditions, suggesting that this is a contributory reason for the poorer perfonnance of the model circuit breaker at this higher current level.

Nonlinearity in the perception of form.

ofcontrast, rather than to contrast itself. This finding mayleadto a new understanding ofthe way in whichthe visualsystem segregates objects from their backgrounds.Visual patterns were created on the face ofa cathoderay tube monitor (Tektronix608) with an electronic visualdisplay instrument (Milkmanet al., 1980) underthe con­trol of a microcomputer (PDP-11/23). The instrumentproduced a raster display. Each frame ofthe raster con­sisted of256 lines with 256 pictureelements perline. Theframe rate was 270 Hz. The visual stimulator producedfour spatial profiles, which could be mapped into eachofthe 256

The raster graphics approach in mapping

Graphics hardware technology is expanding from pen plotters and vector screens to raster. The decade for outstanding advancements in raster output devices, in terms of greater resolution, more colors and greatly reduced costs, is upon us. Ever since the first graphic output devices were developed, discussion as to whether the raster or vector technique is better has occupied computer graphics analysts. There are problems which are easier to solve in one system, but almost impossible to attack in the other. For example, high-precision engineering drafting consists mainly of short line segments, an operation very cumbersome for a raster structure, but simple with the vector technique. On the other hand, solid shaded areas, colored lines of varying thickness and satellite image processing are impossible with vector systems, but natural for a raster display. Recent years developments have concentrated on devices which do not draw straight lines, but instead use a matrix of dots to build up the picture. This method is the raster technique.

Two methods for improving the efficiency of ray casting in solid modelling

In solid modelling based on constructive solid geometry and primitive instancing, ray casting is a very suitable technique for visualization of models on a raster display. In its present form, it is, however, too inefficient for interactive use. Two methods for improving the efficiency are given here. The first uses scan-line interval enclosures instead of box enclosures, and also bypasses non-contributing nodes during each traversal of the CSG (constructive solid geometry) tree. The second refines the image step by step by subdivision, thereby avoiding explicit computation of the intensities of many pixels of the image. The second method reduces computing time more than the first, but has the disadvantage that slivers may occasionally be lost from the image.

Anti-aliased line drawing using brush extrusion

This algorithm draws lines on a gray-scale raster display by dragging a “brush” along the path of the line. The style of the line is determined by the properties of the brush. An anti-aliasing calculation is performed once for the brush itself and thereafter only a trivial additional operation is needed for each pixel through which the brush is dragged to yield an anti-aliased line. There are few constraints on the size, shape, and attributes of the brush. Lines can be curved as well as straight, It is possible to produce lines with a three dimensional appearance.

An introduction to NMR imaging: From the Bloch equation to the imaging equation

The emerging technology of NMR imaging is introduced here as a problem in system identification. We show how selected families of signals may be input into the system (system, in this case, is almost synonymous with patient) in order that the system's responses to these inputs may be directly interpreted in terms of the system parameters. Once identified, a raster display of the system parameters provides an internal image of the patient. Inputs to the system age four-component functions of time. One component describes the strength of an RF signal, and the other three components govern the strength of three spatially varying, independently controlled magnetic fields (the gradient fields) in which the patient is immersed. In response to these inputs some of the protons in the patient, acting in concordance with the Bloch equation, give rise to local fluctuations in the magnetization which are detected with a tuned antenna and a sensitive receiver. The relationship between this output signal and the system parameters is summarized in the imaging equation.

New Products

The VAXstation 100 from Digital Equipment Corporation is the first in a family of high-performance video workstations intended for use with the company's VAX family of 32-bit computers. Featuring a 19-inch, high-resolution, monochrome, 60-Hz noninterlaced raster display and 103-key keyboard, a local display processor with display buffer, and a pointing device, the VAXstation 100 connects via fiber optics to any VAX computer system through a Unibus interface capable of supporting two workstations.

The message is the medium

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.

The interactive manipulation of unstructured images

Conventional approaches to interactive computer graphics do not always seem appropriate for certain kinds of two-dimensional design (e.g. art, graphics). This paper discusses an approach to computer graphics in which the interaction between the man and the machine is viewed as a process of communicating interpretations . The task for the man is to describe the structure perceived in the displayed image. The task for the machine is to derive an interpretation consistent with the user's perception by utilizing the image (the bitmap of a raster display) and the description of it provided by the user. Examples of techniques used in this approach are discussed, including those for handling figure/ground perceptions. It is argued that by using such techniques it is possible for the user to manipulate unstructured images interactively.

An experimental system for creating and presenting interactive graphical documents

An experimental system is described for the design, development, and presentation of computer-based documents that combine pictures and text on a high-resolution color raster display. Such documents can be used, for example, for maintenance and repair tasks, videotex databases, or computer-aided instruction. Documents are directed graphs whose nodes we refer to as pages, in analogy to the pages of a paper book. A page includes a set of simultaneously displayed pictures, actions (procedures and processes), and indexing information. Pages may be nested arbitrarily deeply in chapters that serve much the same organizing function as those of conventional books. The system is comprised of separate programs for laying out and drawing pictures, for graphically specifying the contents of pages, chapters, and their interconnections, and for displaying the document for user interaction. Examples are given from a prototype maintenance and repair manual in which emphasis was placed on designing actions that allow simple real-time animation and assist in finding one's way around the document.

An Examination Of Techniques For Reformatting Digital Cartographic Data / Part 2: The Vector-To-Raster Process

Current graphic devices suitable for high-speed computer input and output of cartographic data are tending more and more to be raster-oriented, such as the rotating drum scanner and the color raster display. However, the majority of commonly used manipulative techniques in computer-assisted cartography and automated spatial data handling continue to require that the data be in vector format. This situation has recently precipitated the requirement for very fast techniques for converting digital cartographic data from raster to vector format for processing, and then back into raster format for plotting. The current article is the second part of a two-part paper that examines the state of the art in these conversion techniques. In Part 1, algorithms to perform all phases of the raster-to-vector process were outlined and compared. This paper outlines and compares algorithms to perform each phase of the vector-to-raster process. Methods for combining these algorithms into an efficient, integrated process are presented; they are followed by a discussion of the raster-to-vector conversion process as a whole including commonalities, methods for improving the overall process, and directions for future research.

An Examination Of Techniques For Reformatting Digital Cartographic Data / Part 1: The Raster-To-Vector Process

Current graphic devices suitable for high-speed computer input and output of cartographic data are tending more and more to be raster-oriented, such as the rotating drum scanner and the color raster display. However, the majority of commonly used manipulative techniques in computer-assisted cartography and automated spatial data handling continue to require that the data be in vector format. This situation has recently precipitated the requirement for very fast techniques for converting digital cartographic data from raster to vector format for processing, and then back into raster format for plotting. The current article is part one of a two-part paper concerned with examining the state-of-the-art in these conversion techniques. In part one, algorithms to perform all phases of the raster-to-vector process are systematically outlined, and then compared in general terms. Examples of existing implementations of the raster-to-vector process are also described and evaluated. Part two will outline and compare algorithms to perform the reverse process, vector-to-raster conversion. Part two will also discuss raster-to-vector and vector-to-raster conversion as an integrated process.

A general purpose graphic system for computer aided design

The experimental Advanced Integrated Designer's Activity Support (A-IDAS) system is intended to be a base for a total engineering system rather than a pure graphic system. The system provides a database in which graphic data, geometric data and engineering data are stored in a relational data model. It also provides a graphic management facility which can manipulate not only pictures drawn with lines, but those drawn as areas. Areas are represented by crosshatched lines or colors. In more complicated ways, they can be represented as texture or scenery. The system controls two kinds of graphic display devices: a vector display and a raster display. These devices are supported through a device independent user interface when pictures are drawn with lines. With this experimental system, it has been found out that one can develop an engineering system having fairly general purpose capabilities.

The use of grayscale for improved raster display of vectors and characters

Decreasing memory costs will soon allow grayscale displays in low-cost raster graphic terminals. Subtle shadings can be used to provide improvements in line quality and character flexibility which could allow raster displays to compete on better terms with the more expensive calligraphic displays. Algorithms for achieving smooth vectors and rotatable dot matrix characters are outlined and scan conversion is discussed. A discussion of the relation between image quality and number and distribution of gray levels follows, with concluding remarks on costs and other practical matters.

How to color in a coloring book

Children's coloring books contain line drawings which a child can fill in with a crayon to produce colored pictures. Two dimensional colored areas can be produced on a raster display by an analogous method. After drawing a closed curve with line drawing commands, the graphics system can fill the area bordered by the curve. This paper presents an algorithm for filling in areas of any size or shape. The area may be filled with any color, texture, or “wallpaper” pattern. The algorithm is simple, flexible and efficient, optimized to take advantage of the the memory organization of most current raster graphics systems.

Design of a Raster Display Processor for Office Applications

In recent years there has been a pronounced emphasis to develop alphanumeric display systems for document creation, filing, and text editing applications. This paper describes the design of a raster scan Display Processor which was specifically implemented to produce full page images ( 8½ in × 11 in or 11 in × 8½ in) which emulate typewriter output. A dual data path architecture is presented in which a Character Generator produces video images of text data, while a FAX Generator generates bit map video images corresponding to graphic forms used in the office. The design approach chosen provides degrees of functional richness that are not commonly present in current systems. Furthermore, the modular approach allows for a choice of whether or not to include forms overlay capability based on application requirements.

Improving interaction with a raster display

Interacting with a raster display can be frustratingly slow if images must be transmitted over slow data links such as standard telephone lines. When interaction with a graphics terminal is based on the system displaying detailed pictures and then a response by the user, the slow row-by-row painting method should be replaced by a hierarchical refining scheme discussed here. The small overhead in the refining scheme is a small price to pay for increased convenience to the human.