+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ BESSER * Implications of disseminating images on the network; planning the distribution of multimedia documents poses two critical implementation problems * Layered approach represents the way to deal with users' capabilities * Problems in platform design; file size and its implications for networking * Transmission of megabyte size images impractical * Compression and decompression at the user's end * Promising trends for compression * A disadvantage of using X-Windows * A project at the Smithsonian that mounts images on several networks * +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
Howard BESSER, School of Library and Information Science, University of Pittsburgh, spoke primarily about multimedia, focusing on images and the broad implications of disseminating them on the network. He argued that planning the distribution of multimedia documents posed two critical implementation problems, which he framed in the form of two questions: 1) What platform will one use and what hardware and software will users have for viewing of the material? and 2) How can one deliver a sufficiently robust set of information in an accessible format in a reasonable amount of time? Depending on whether network or CD-ROM is the medium used, this question raises different issues of storage, compression, and transmission.
Concerning the design of platforms (e.g., sound, gray scale, simple color, etc.) and the various capabilities users may have, BESSER maintained that a layered approach was the way to deal with users' capabilities. A result would be that users with less powerful workstations would simply have less functionality. He urged members of the audience to advocate standards and accompanying software that handle layered functionality across a wide variety of platforms.
BESSER also addressed problems in platform design, namely, deciding how large a machine to design for situations when the largest number of users have the lowest level of the machine, and one desires higher functionality. BESSER then proceeded to the question of file size and its implications for networking. He discussed still images in the main. For example, a digital color image that fills the screen of a standard mega-pel workstation (Sun or Next) will require one megabyte of storage for an eight-bit image or three megabytes of storage for a true color or twenty-four-bit image. Lossless compression algorithms (that is, computational procedures in which no data is lost in the process of compressing [and decompressing] an image—the exact bit-representation is maintained) might bring storage down to a third of a megabyte per image, but not much further than that. The question of size makes it difficult to fit an appropriately sized set of these images on a single disk or to transmit them quickly enough on a network.
With these full screen mega-pel images that constitute a third of a megabyte, one gets 1,000-3,000 full-screen images on a one-gigabyte disk; a standard CD-ROM represents approximately 60 percent of that. Storing images the size of a PC screen (just 8 bit color) increases storage capacity to 4,000-12,000 images per gigabyte; 60 percent of that gives one the size of a CD-ROM, which in turn creates a major problem. One cannot have full-screen, full-color images with lossless compression; one must compress them or use a lower resolution. For megabyte-size images, anything slower than a T-1 speed is impractical. For example, on a fifty-six-kilobaud line, it takes three minutes to transfer a one-megabyte file, if it is not compressed; and this speed assumes ideal circumstances (no other user contending for network bandwidth). Thus, questions of disk access, remote display, and current telephone connection speed make transmission of megabyte-size images impractical.
BESSER then discussed ways to deal with these large images, for example, compression and decompression at the user's end. In this connection, the issues of how much one is willing to lose in the compression process and what image quality one needs in the first place are unknown. But what is known is that compression entails some loss of data. BESSER urged that more studies be conducted on image quality in different situations, for example, what kind of images are needed for what kind of disciplines, and what kind of image quality is needed for a browsing tool, an intermediate viewing tool, and archiving.
BESSER remarked two promising trends for compression: from a technical perspective, algorithms that use what is called subjective redundancy employ principles from visual psycho-physics to identify and remove information from the image that the human eye cannot perceive; from an interchange and interoperability perspective, the JPEG (i.e., Joint Photographic Experts Group, an ISO standard) compression algorithms also offer promise. These issues of compression and decompression, BESSER argued, resembled those raised earlier concerning the design of different platforms. Gauging the capabilities of potential users constitutes a primary goal. BESSER advocated layering or separating the images from the applications that retrieve and display them, to avoid tying them to particular software.
BESSER detailed several lessons learned from his work at Berkeley with Imagequery, especially the advantages and disadvantages of using X-Windows. In the latter category, for example, retrieval is tied directly to one's data, an intolerable situation in the long run on a networked system. Finally, BESSER described a project of Jim Wallace at the Smithsonian Institution, who is mounting images in a extremely rudimentary way on the Compuserv and Genie networks and is preparing to mount them on America On Line. Although the average user takes over thirty minutes to download these images (assuming a fairly fast modem), nevertheless, images have been downloaded 25,000 times.
BESSER concluded his talk with several comments on the business arrangement between the Smithsonian and Compuserv. He contended that not enough is known concerning the value of images.
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