Opto-Electronic Storage–An Alternative To Filming?

Commission on Preservation and Access

February 1993
Newsletter Insert

Opto-Electronic Storage–An Alternative To Filming?

Translation of a chapter from the article
“Verfilmen oder Instandsetzen?
Schutz- und Ersatzverfilmung im Dienste der Bestandserhaltung”by
Dr. Hartmut Weber

Commission Introduction

To contribute to the continuing discussions of digital technology and microfilming for preservation and access, the Commission presents the following view from Germany. “Opto- Electronic Storage–an Alternative to Filming? ” is a translation from German of a chapter from a longer article by Dr. Hartmut Weber, “Verfilmen oder Instandsetzen? Schutz- und Ersatzverfilmung im Dienste der Bestandserhaltung, ” (Filming or Repairing? Protective and Replacement Microfilming for Preservation) published in Bestandserhaltung in Archiven und Bibliotheken (Preservation in Archives and Libraries), edited by Dr. Weber (Verlag W. Kohlhammer, Stuttgart, 1992). Dr. Weber is the director and department head at the archives administration of the federal State of Baden-Württemberg, responsible for conservation policy in archives and libraries of the State of Baden-Württemberg. He is a member of the Committee on Image Technology of the International Council on Archives and has lectured and written extensively about preservation problems in archives and libraries.

We would like to explore whether micro-media are safe for the future or whether they will soon be replaced by other storage media, in particular the opto-electronic ones.

As a timely alternative to microfilm for image storage, the optical storage disk, the so-called optical disk, is being considered. [1] In particular, the WORM-disk (write once, read many times) or the medium MOD (magneto optical disk) which can be erased and re-written are pointed out, since recordings on these storage units can be made in-house, while the popular CD-ROM (compact disk read only memory) can only be economically produced industrially and in large numbers.

The optical storage disk stores coded information by contents or uncoded information by image by means of a digital recording procedure. In principle, it can be compared to magnetic storage units, which can store digitized images in addition to data almost permanently. With the opto-electronic storage procedure, the digitized information is burnt into a metal-coated plastic disk, in the most commonly used procedure for instance by means of a laser beam and an optical system. This results in tiny indentations, “pits,” which can then also be recognized by laser optics.

In digital image storage–which is the only alternative to microfilming–the graphic master is read via a scanner and resolved into dots. Compression software makes it possible that the images do not have to be stored in a binary pattern of 1:1, i.e., storage intensively and uneconomically. The recording quality essentially depends on the number of dots into which the graphic master is resolved.

The storage and evaluation of information stored on optical disks necessitates a relatively expensive computer system with suitable components of hardware and software. The stored graphic masters, equipped with search addresses, can be represented on a high resolution screen and/or printed on output devices such as laser printers.

The advantage of the optical storage disk is the relatively quick access to a large number (tens of thousands) of information pieces or documents stored in this manner. The search and response times are in the range of seconds somewhere between those of the magnetic media, which are definitely superior in speed to the optical disk, and those of a microfilm retrieval system.

The recording quality of systems with optical storage disks depends on the performance of the scanners and, with a resolution of 200, 300, or at present maximally 400 dpi, is rather poor in comparison with microfilm with a resolution of practically over 1000 dpi [2] (of the graphic model, not the film): quality typographic resolution in phototypesetting also begins at 1000 dpi. For printed matters and typewritten documents this quality is, no doubt, sufficient, but in case of handwritten documents, pencil notes, etc., the limits are quickly reached where information appears visibly “frayed” into dots. In such systems, the reproduction of grey tones is limited and affects the storage capacity and thereby also the efficiency even more than a higher resolution does. Color reproduction is so far not economically possible with digital image storage [3]

Optical storage disks are available in sizes 3 1/2″, 5 1/4″, 12″, and 14″. Evidently, a 14″ disk of one manufacturer cannot be used with a 5 1/4″ disk drive which the same manufacturer propagates a few years later. But even the same disk size does not guarantee compatibility. There are no national standards for opto-electronic data storage – not to mention international standards. This is particularly true for recording formats. So far, no industry standard given by a manufacturer has become generally accepted. Disks and disk drives by different manufacturers are not compatible, and even the systems of one manufacturer may be incompatible for the same disk size. [4]

The optical disks of all technologies known so far are not age resistant, since the media are very sensitive to oxidation or corrosion. In case of digital recording techniques, only a few “bit errors” are sufficient to make an entire disk illegible. Opto-electronic storage media have been available only since 1982, so that their expected durability could so far only be predicted on the basis of numerous tests with accelerated aging methods. [5] Legibility would be between 10 and 30 years, depending on the recording technique and the disk material. Manufacturers state 50 or 100 years for special combinations of materials such as the gold or platinum basis for WORM disks. Such statements should, however, still be taken with a grain of salt. [6] Professional users in the service sector copy the WORM disks after 10 years. [7] One manufacturer guarantees a durability of 50 years for an erasable, opt-magnetic disk, provided that the disk is copied every 5 years, i.e., newly recorded. This means that the optical storage disk is only conditionally suitable as an archive medium. Provisions must be made for copying the disks at regular intervals, which means reading the old disk and recording the information on a new disk via a computer. Quite apart from the expenditure in machinery, the reservation of computer time and the computer capacity, the necessary, disks are relatively expensive, and the old disks, at least the WORM disks, can no longer be used. As a rule, the duplicate can only be used in an identical system as far as hardware and software are concerned.

Durability of the media is, however, not the main problem in the evaluation of suitability for the required durable storage of information in archives or libraries. [8] They will always outlast the availability of the systems. As experience has shown, the innovation cycle is very short for any data processing equipment; hardware is surpassed a few months after its initial development and obsolete after five years. Thus, support of the system through the manufacturer or distributor can become a problem after a few years. “It is inherent in these machines that they become outmoded and die before having passed on their capacities to their progeny.” This statement by Harald Heckmann points out the indubitably most important problem in the preservation of any kind of information which is no longer available to man without complicated technology. [9] Analogous information on a microfilm can be read comfortably with relatively minor expenditure (light source, optics), if necessary also by daylight with a magnifying glass, since it is “eye-legible.”‘ [10] Reading digitized information requires expensive technology with hardware and software components which are subject to rapid change. Who can still do anything with punched cards or punched tapes nowadays? Who still has a disk drive for 8″ disks, which were almost the standard a few years ago? If opto-electronic media are to be used as durable storage units for information, all media have to be converted immediately as soon as a new generation of devices appears on the horizon. This is the only way to avoid the danger that these media become technically outdated and thereby incompatible.” [11] The modern high tech systems become obsolete particularly fast. Microfilm, on the other hand, which has been known and proven for 150 years and has been declared dead again and again, does not even become obsolete and is always compatible with the most modern systems.

An economic comparison also proves that microfilm is superior. Personnel requirements are much higher for opto-electronic storage systems during recording and indexing of documents than for microfilming. The collecting of search criteria and search addresses is essential for an orderly recording of documents in systems with optical storage disks, but it is unnecessary for sequential filming. Studies by the Association for Economic Administration reveal the following cost relationship so far: the cost of storing one page/year is DM 0.08 with microfilm, but DM 0.49 with an optical storage disk. [12] For archive material which cannot be filmed in a cost-effective production run, the cost relation changes somewhat in favor of optical storage disks, as shown by a pilot project of the National Archives in Washington.’ [13] According to this study, the personnel and equipment expenditures for a document imaging system using optical storage disks are two times higher than the costs for a computer aided/supported microfilm retrieval system with a nearly similar efficiency and three times higher than a traditional microfilm system without automatic retrieval facilities.

The optical storage disk can therefore be recommended only for applications in which frequent, timely access to a limited information base is essential, provided that the preservation of these data is solved in another way and there are no high demands for quality. It is an access medium, a medium for use. The optical storage disk is not a reliable storage medium for image recordings, since it does not have sufficient recording quality nor age resistance and since the future availability of compatible systems is very doubtful because of the lack of norms and standards. The optical storage disk cannot replace microfilm, an established, safe, age resistant and economical storage medium with high recording quality; it can, at most, supplement it in hybrid systems. In such systems the processing and distribution even of uncoded image information takes place digitally. The basis for this is microfilm as an age resistant, analogous storage component.

At any rate, filming for protection should first of all be done with a high-quality microfilm as an age resistant storage medium. This achieves protection and permits the use with means that are in keeping with the economy of the system. If additional means for use and more comfortable access are to be employed or if the images are to be made available in digitized form and interleaved with coded search information, it is quite possible to do this by means of systems with opto-electronic storage disks or similar devices – at some expense. The expense for the preceding filming for protection is by no means lost. Microfilming secures the investments. Nowadays, films can already to the basis for digitized image conversions for the purpose of use. They will be able to fulfill this purpose again and again in the future, when predictably still more efficient systems make access to the image recordings easier and easier and increase quality. Microfilms as analogous image storage media guarantee upward compatibility. The electronic access systems themselves cannot achieve this: a graphic master, once digitized with 200 dpi, can still only be looked at with the lesser resolution even in a subsequent system that gives a resolution of 600 dpi, unless the original is re-scanned with the higher resolution – and that is, of course, not the idea of preservation. The correct rule that each page of a book or other archive material should, if possible, only be handled once in connection with preservation measures should certainly not be broken for high tech systems because of their nature. A quality microfilm has a reproduction quality from the very start which will leave nothing to be desired even in the future. Thus, filming coupled with modern information access systems not only contributes to technical progress, but, more importantly, to the preservation of the originals through the scanning of microfilms, which is also more cost-effective.


1. A summarized, up-to-date survey of opto-electronic media presently available, by K. Schlaepfer: “Optical Storage Disks for Archiving Documents. Present Status,” in: ARBIDO Spécial: Konservierung- Restaurierung. volume 6 (1991), pages 96-; see also Hans Hagemann, “From Microfilm to Cl) ROM,” in: Nachrichten für Dokumentation 41, (1990), pages 245-; Wilhelm Lenz, “Optical Disk or Microfilm?” in: Der Archivar 41(1988), volume 1, columns 99-104.

2. The resolution capacity of the films themselves is much higher. A film image of 24 X 36 mm can represent more than 50 million image dots (pixel), i.e., ten times as many as the best scanner-sensor ut present resolves (information courtesy Kodak AG, Stuttgurt).

3. Thus, a digitized color image on a photo-CD (Kodak) still takes up memory space of 5 megabytes, even after compression of the original 18-20 megabytes per image, and still does not achieve the reproduction quality of a color transparency.

4. See K. Schlaepfer: “Optical Storage Disks for Archiving Documents.”

5. A new, comprehensive compilation of Literature about durability risks and durability expectations of opto-electronic media by William Saffady, Stability. Care and Handling of Microforms. Magnetic Media and Optical Disks. Library Technology Reports, American Library Association, January-February 1991, pages 72 -.

6. See also Hans Hagemann, “From Microfilm to CD-ROM,” page 245; K. Schlaepfer, “Optical Storage Disks for Archiving Documents,” page 102.

7. Information courtesy INFEUROPE, Luxembourg: this company has been commissioned by the Office for Official Publications of the European Community to make these publications of the EC accessible for a longer time by means of a FileNet-system on the basis of WORM storage media.

8. The author has so far not been able to find any confirmation in library circles for the statement of Hans Hagemann, “From Microfilm to CD ROM,” page 244, according to which the “actual storage in library sense comprises a time span of 400 years.”

9. Quoted according to Franz Georg Kaltwasser, “Restoration and Preservation as the Task of Libraries. The Conference on Preservation of Library Materials in the Austrian National Library, Vienna, April 7 through 10, 1986”, in: Zeitschrift für Bibliothekswesen und Bibliographie, Journal for Library Science and Bibliography), 33 (1986), page 353.

10. It is astonishing that in comparisons of microfilming systems and optical storage systems (WORM) reference is often made to the “weak mechanism” of microfilming systems but none to the rapid technological obsolescence of optical storage systems–see “New media in the TIB and their effect on the national supply of literature,” a final report of a BMFT-project, Hannover 1990, pages 41- and 44. (BMFT refers to the Ministry for Research and Technology, “Bundesministerium für Forschung und Technologie.”).

11. See K. Schlaepfer, “Optical Storage Disks for Archiving Documents,” page 104.

12. AWV Informationen, volume 34, number 10, October 1988, page 6.

13. National Archives and Records Administration (publishers), Optical Digital Image Storage Systems. Project Report, Washington 1991, pages 290 -.