Introduction to Multimedia in Museums

Section Two: Developing Multimedia Systems


6. Multimedia Formats

This chapter consists of the following sections:

Introduction

Different types of media can be represented in different data and technical formats. These may be integrated within one system or application to greater or lesser degrees.

Formats apply to elements of systems and to elements of data content as well as to different stages in creating and using multimedia applications. Only some formats are specific to multimedia applications with many existing already as 'monomedia' formats.

Standards may exist for system formats and/or data formats, for production and use of multimedia applications, with some applicable at different stages in the creation process, as well as for the interchange of information. Standards can standardize formats in different ways, within one system or across systems. They may be operational specifications with some being protocols or sets of procedures for communication.

Formats may become standards in themselves, with new products creating de facto standards. These may or may not be accepted formally by official standards organizations. The latter may be national or international or may relate to a particular segment of industry or interest group with differing degrees of authority and acceptability. Official standards often emerge from or build on de facto standards. More rarely standards may exist officially but not be applied nor have become widely acceptable.

The importance of applying standards cannot be over emphasized. They make possible the maximum use and re©use of data and work done, where resources are often limited, as well as facilitating the exchange of data both within the museum community and more widely.

System Formats

Multimedia applications in museums may be used for many different purposes such as: temporary exhibition enhancement; guides to collections or buildings, within a gallery or outside a museum; archival or collection management systems; access or retrieval systems,internal or external, perhaps networked; multimedia publications. The particular purpose should influence the choice of systems and formats.

Multimedia hardware formats may include PC's, TV players, electronic books and other hand held devices. Elements for input, storage and output may include scanners, cameras, WORM disks, CD-ROM, CD-I, etc. In the following paragraphs some equipment and related formats are discussed.

Input

Digital or conventional cameras for stills or video, scanners, audio recording devices and computers may provide input. If a high resolution still image is needed, or the blowing up of a detail in an image, then a scanned image is necessary rather than a video image or one from a mobile digital camera. Low end flatbed scanners are comparatively inexpensive and adequate for black and white images but some may have poor color sensitivity, and do not provide for a good hard copy output from a system if that is a requirement. High end flat bed scanners are more expensive, and many may provide high quality images with good colors.

The limitation of both types is that the format to be scanned is normally A-4, although larger scanners exist but at considerable higher cost. High resolution, direct negative scanners or fixed digital cameras for large format negatives are expensive, although images from 35mm film can be produced at a reasonable cost, particularly from Photo CD, which will be adequate for many purposes. Photo CD, however, is reliant on image capture by a bureau or company operating under license, or in-house requiring an expensive and powerful scanner and workstation, again under license. In all cases the resulting files are big, requiring large storage devices.

Video input, although quick and comparatively cheap to produce, suffers even more from technical limitations for use as full motion video than for still images. Animation suffers from the same limitations although it is now much easier to produce using computer technology. Especially moving images require large amounts of computer memory for their storage and manipulation.

Graphics are generally well catered for in their creation in digital form, although considerable care is needed in conversion from paper form to digital form. Color, and black and white, photographic images and graphics may require different scanners appropriate for the different type of image, i.e. color, monochrome or grey scale.

Audio quality is more dependent on the output mechanism than the well established input formats.

Data may of course be manipulated once input. Authoring tools are a form of software particularly applicable to multimedia. Formats vary too greatly to discuss in detail with packages often using their own internal formats for authoring and editing.

Storage and Output

Storage may be in the form of a variety of magnetic, optical or magneto-optical media, analogue or digital, mainly computer based. These include videodiscs, CD-ROMs, writable and write once disks, DAT tapes, Video CD, Photo CD, CD-R, CD-I, DVI, 3DO.

Videodiscs store still and moving video images in analogue format. They need the combination of a videodisc player and a computer system to be fully interactive. They have a large image capacity (54,000 to 76,000 per side) and handle motion video well, but the image quality is limited and production costs are high if use is made of videodiscs which have to be produced using a master disc. Writable videodiscs are much cheaper. However, analogue master images are of limited value for reuse.

CD-ROM discs have a large storage capacity, especially for text,(1/4 million pages A4), although image numbers are limited, but can be of a high quality (2000 high resolution color images). Up to 20 hours of recorded speech can be stored, or various combinations of different media. They are read by a computer system only, with a CD-ROM drive or several drives in a jukebox. The speed of access to data is improving but they are better as a publication and distribution format than for permanent storage as an archive. CD-ROM discs are produced using a master disc. The CD-R (recordable) may be written by the user, although the process is still slow and therefore only suitable for limited editions.

Other optical disks, WORM (write once, read many), and rewritable, have a much larger capacity, and can be accessed quickly, held online on a multiple drive system, or via a jukebox. As they are relatively expensive they are more suited for use by organizations with large data requirements. Rewritable disks also provide a means of readily updating contents. Although WORM CD-ROM discs, known as CD-R (see above) have been developed now, allowing cheaper in-house proofing or small scale production of CD-ROMs, there are no rewritable ones yet.

The Kodak Photo CD stores color images on standard 12cm compact discs, which can be displayed on a TV screen using a CD player (some versions are available which play audio and photo discs), or on a VDU through a compatible CD-ROM drive linked to a computer. This must have multi session capability to allow it to read Photo Cd's, or CD's that have been written to more than once. It should also be at least double speed (preferably triple speed) to access data with sufficient speed. About 100 35mm images can be stored on a Photo CD at photographic quality, or up to 800 at the equivalent of TV resolution, or 6,000 as low resolution thumbnail images.

CD-I (Compact Disc Interactive) adds the full range of media capability to audio discs, and is playable on any CD-I player attached to a TV set, with access by questions or menus as with interactive video. As it is a digital medium the images are archived in a higher resolution than video and than they appear on the screen with present technology. It is a relatively cheap and flexible medium.

DVI is a competing standard to CD-I as it enables storage and playback of visual and audio data digitally. It is basically a compression format for moving images which allows 1 hour of full motion video and audio on a CD©ROM to be played back on a computer, but development and distribution costs are high.

Video CD converts VHS quality video to digital form, to a format agreed by MPEG. With the addition of a special full©motion video cartridge Video CD's can be played on CD-I and some CD ROM machines.

3DO is a multimedia consumer platform similar to CD-I with improved 3D graphic animation.

HDTV (High Definition TV) currently has three competing formats, analogue and digital, giving a higher resolution display than has previously been possible on a TV screen, about 2000 x 2000 pixels and equivalent to 35mm film quality.

These formats may also be regarded as output or delivery formats, with physical distribution on optical discs for example. Digital storage media also include DAT's (digital audio tapes), tape drives, Winchesters (hard disc), writable optical drives. Digital formats, particularly CD-ROMs, may be distributed via networks such as ISDN (Integrated services digital network) or LAN's (local area networks).

Alternative output devices are VDU's for soft display, printers for hard copy or desk top publishing systems. Hard copy output requires higher resolution images than machine read output, unless it is acting as a form of note or reminder when the quality equivalent of a photocopy may be sufficient. Good quality printers are expensive. CD-ROM is currently seen as the most favorable format for electronic publishing.

Content Formats

Content of multimedia applications may include data in combinations of the following formats: still images, graphics, motion video, animation, text, numbers, sound, storyline and interface. Image files may be put in various standard formats for interchange purposes. These may also be used for editing and storage. The formats explain what encoding system is used to compress the image and how the image information is organized, with additional header information about the image as well.

Different formats relate to different ways of representing images, eg. raster, vector or textual representations. Examples are TIFF, PCX, Targa, GIF, IFF/LBM, bitmaps, Cals type 1&2, bitmap graphics. File formats exist for other media such as ASCII for text, MIDI for audio, HDTV for video.

Formats for image storage and display are often described in terms of image resolution. This is a combination of the number of pixels across and down the image. Resolutions of stored images may be higher than the relevant display device can make use of. The number of colors available (reflected in the standard used e.g. VGA, SVGA) also affects the picture quality, especially with digitized images rather than graphics. Photo CD formats Pro-Master, Master 35mm, Portfolio, and Catalogue equate to diminishing levels of resolution from 4096 x 6144 pixels down to 128 x 192 pixels. These are useful for different purposes with high resolution for high quality publishing output and low resolution to enable many images to be displayed at once or browsed through quickly.

Stored data may be compressed to reduce the space needed with various formats and standards for image, audio and video compression and decompression for transmission and display.

Examples are JPEG, fractals, (both handling color and grey scale images), CCITT Groups 3&4 (for monochrome images); JBIG (modification of JPEG) for raster images; MIDI for audio; MPEG and DVI for video and associated audio. Photo CD images use their own color encoding metric, Photo YCC, optimized for TV display and printing, but which is not an official standard. They have to be read into another file format for manipulation. Some of these compression formats cause more loss of data than others, and in some applications this may be of considerable importance.

Standards

MHEG (Coded Representation of Multimedia and Hypermedia Information Objects ISO CD 13522), from the Multimedia, Hypermedia information coding Expert Group, a draft standard, is the nearest to an overall standard for multimedia, at a high level. Reference needs to be made to various other areas of standards within this, or in addition to this, such as those for various monomedia elements contributing to multimedia. Many of the relevant standards are important to data interchange and are specified by the CIMI Standards Framework.

System Standards

In addition to the various so called standards for general computer systems which tend to be set by the manufacturers and are really proprietary or possibly de facto standards, there are some developments specific to multimedia systems. These include the MPC standard, a base specification for a multimedia PC, and interface standards such as MCI (Media Control Interface), HCI (Human Computer Interface ISO 9241 under development), and API (Application Programming Interface). Some 'standards' are beginning to develop for software, and standards for the development of systems, including multimedia systems, which may eventually become ISO's. The IMA (Interactive Multimedia Association) is industry led, producing recommended practices and is currently working on multimedia system services, data exchange and scripting languages.

Capture and Encoding Standards

For scanning quality control and OCR (Optical Character Recognition) procedures and preparation various national standards exist, such as North American ANSI standards.

ODA (Office Document Architecture) and SGML (Standard Generalized Markup Language, ISO 8879) are standards for describing electronic documents, for document interchange. They can also be used for hypertext, which is often used in multimedia applications. These two standards have been developed to define formats for presentation of multimedia and hypermedia information, and are also necessary for editing and manipulating, and for facilitating interchange of such data between applications. MHEG (Coded Representation of Multimedia and Hypermedia Information Objects, draft ISO CD13522) is extending the standards for text to include other data and media. Hytime (Hypermedia/Time-Based Document Structuring Language, ISO 10744 extends the markup of single documents using SGML to multiple data objects or documents.

For data compression encoding various standards exist for different media, e.g. JPEG (Joint Photographic Experts Group) for the digital coding of still images, MPEG (Motion Picture Experts Group) for motion picture and associated audio. For data encoding many standards exist which are really de facto standards rather than being formally accepted as standards. These include the file formats mentioned earlier. The widely used TIFF Image File Format is one. However there are different versions of TIFF files which may not be compatible.

Storage and Retrieval Standards

CD-ROM is the most standardized and widely used of optical media. Standards exist for the physical and optical characteristics of optical discs. The major disc sizes have different format standards, with some national and ISO standards in place. The CD-ROM format is ISO 10149 for the recording format, with ISO 9660 for the 'logical format', i.e. the file structure. All Photo CD disc formats conform to this. It should be noted that there are off shoots from the main ISO 9660.

Many WORM media and drives use proprietary standards. 5.25" WORM format discs have 3 different incompatible standards. ISO 9171 covers both formats A and B. Larger optical discs have some draft standards.

5.25" and 3.5" rewritable optical discs have ISO standards which are adhered to, but some imaging systems use non standard discs.

Volume and file structure standards enable operating systems to understand and access files. The Yellow Book standard for CD-ROM and CD-ROM XA covers the use of audio and video with computer data. The Green Book standard covers CD©I with its better audio and video image quality. A new White Book covers the CD standard for Digital Video. An Orange Book standard covers CD©R discs. For display standards see the earlier section on content formats. Note should be taken that Apple machines and PCs differ in the way they store data for screen display and files in the same format may not translate from one to the other.

Where ISO or national standards relevant to multimedia exist they should be specified in any project requirement along with the instruction to specify what standards are adopted for particular aspects of a product or system where there may be a choice.


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5. Project Defintion 7. Project Management