Jane C. Blake,
Managing Editor

This issue of the Digital Technical Journal features papers on multimedia technologies and applications, and on uses of the Application Control Architecture (ACA), Digital's implementation of the Object Management Group's CORBA specification.

The high quality of today's television, film, and sound recordings have set expectations for computer-based multimedia; we expect high-quality images, fast response times, good quality audio, availability - including network transmission, and all at "reasonable" cost. Bob Ulichney has written about video image-rendering methods that are in fact fast, simple, and inexpensive to implement. He reviews a color rendering system and compares techniques that address the problem of insufficient colors for displaying video images. Dithering is one of these techniques, and he describes a new algorithm which provides good quality color and high-speed image rendering.

The dithering algorithm is utilized in Software Motion Pictures. SMP is a method for generating digital video on desktop systems without the need for expensive decompression hardware. Burkhard Neidecker-Lutz and Bob Ulichney discuss issues encountered in designing portable video compression software to display digital video on a range of display types. SMP has been ported to Alpha AXP, Sun, IBM, Hewlett-Packard, and Microsoft platforms.

Digitized data - video or audio - must be compressed for efficient storage and transmission. Davis Pan surveys audio compression techniques, beginning with analog-to-digital conversion and data compression. He then discusses the Motion Picture Experts audio algorithm and the interesting problem of developing a real-time software implementation of this algorithm.

Even compressed, digitized data takes up tremendous amounts of storage space. A relational database can not only store this data but provide fast retrieval. Mark Riley, Jay Feenan, John Janosik, and T.K. Rengarajan describe DEC Rdb enhancements that support multimedia objects, i.e., text, still frame images, compound documents, and large binary objects.

Managing image documents is the subject of a paper by Jan te Kiefte, Bob Hasenaar, Joop Mevius, and Theo van Hunnik. Megadoc is a hardware and software framework for building customized image management applications quickly and at low cost. They describe the UNIX file system interface to WORM drives, a storage manager, and an image application framework.

Distributing multimedia over a network presents both engineering challenges and opportunities for applications. DECspin is a real-time, desktop videoconferencing application that operates over LANs or WANs, using TCP/IP or DECnet protocols. Larry and Ricky Palmer present an overview of the DECspin graphical interface. They then address network issues of real-time conferencing on non-real-time networks and a solution to network congestion.

The transmission of full-motion video programs to multiple users requires adaptations in many parts of a client-server, LAN environment. Peter Hayden's paper focuses on the specific problem of efficient allocation of network addresses for the transmission of digital video data on a LAN. He reviews alternatives and describes a technique for the dynamic allocation of multicast addresses.

The common theme of two final papers is ACA Services, Digital's implementation of the OMG's Common Object Request Broker Architecture. Paul Patrick has written an instructive paper on CASE environment development utilizing ACA. Assuming a multivendor, distributed environment, he discusses modeling of applications, data, and operations; application interfacing; and environment management.

DEC @aGlance software is an implementation of ACA that supports the integration of manufacturing process information systems. David Ascher differentiates between generic integration software and @aGlance, and describes how ACA is used to integrate independently developed applications.

The editors thank John Morse, engineering manager, Corporate Research, and Mary Ann Slavin, engineering manager, ACA, for their help in preparing this issue.