Microform

Microform

[mahy-kruh-fawrm]
Microforms are any form, either films or paper, containing microreproductions of documents for transmission, storage, reading and printing. Microform images are commonly reduced about 25 times from the original document size. For special purposes, greater optical reductions may be used.

All microform images may be provided as positives or negatives, more often the second.

Three formats are common: microfilm (reels), aperture cards and microfiche (flat sheets). Microcards were similar to microfiche, but printed on paper cardboard rather than photographic films.

History

Using the Daguerreotype process, John Benjamin Dancer was one of the first to produce micro-photographs, in 1839. He achieved a reduction ratio of 160:1. Dancer perfected his reduction procedures with Frederick Scott Archer’s wet collodion process, developed in 1850-51, but he dismissed his decades-long work on micro-photographs as a personal hobby, and did not document his procedures. That microphotography could be no more than a novelty was an opinion shared by the 1858 Dictionary of Photography, which called the process “somewhat trifling and childish.”

Microphotography was first suggested as a document preservation method in the early 1850s – in 1851 by James Glaisher, an astronomer, and in 1853 by John Herschel. Both men attended the 1851 Great Exhibition in London, where the exhibition on photography greatly influenced Glaisher: he called it "the most remarkable discovery of modern times," and argued in his official report for using microphotography to preserve documents.

The developments in microphotography continued through the next decades, but it was not until the turn of the century that its potential for practical usage was seized by a wider audience. In 1896, Canadian engineer Reginald A. Fessenden suggested microforms as a compact solution to engineers' unwieldy, but frequently consulted materials. He proposed that up to 150,000,000 words could be made to fit in a square inch, and that a one foot cube could contain 1.5 million volumes.

In 1906, Paul Otlet and Robert Goldschmidt proposed the livre microphotographique as a way to alleviate the cost and space limitations imposed by the codex format. Otlet’s overarching goal was to create a World Center Library of Juridical, Social and Cultural Documentation, and he saw microfiche as way to offer a stable and durable format that was inexpensive, easy to use, easy to reproduce, and extremely compact. In 1925, the team spoke of a massive library where each volume existed as master negatives and positives, and where items were printed on demand for interested patrons.

At the annual meeting of 1936, the American Library Association endorsed microforms. Before this official acceptance, microforms were used in related fields: between 1927 and 1935, the Library of Congress microfilmed more than three million pages of books and manuscripts in the British Library; in 1929 the Social Science Research Council and the American Council of Learned Societies joined to create a Joint Committee on Materials Research, which looked closely at microform’s potential to serve small print runs of academic or technical materials; in 1933, Charles C. Peters developed a method to microformat dissertations; in 1934 the United States National Agriculture Library implemented the first microform print-on-demand service, which was quickly followed by a similar commercial concern, Science Service, and in 1938 University Microfilms was established and the Harvard Foreign Newspapers Microform Project was implemented.

In 1940, the format most broadly used today – microfilm – was developed. Formats it bested include the Photoscope, the Film-O-Graph, the Fiske-O-Scope, filmslides.

Early cut sheet microforms and microfilms (to the 1930s) were printed on a nitrate film and pose high risks to their holding institutions, as nitrate film is explosive and flammable. From the late 1930s to the 1980s, microfilms were usually printed on a cellulose acetate base, which is prone to tears, vinegar syndrome and redox blemishes. Vinegar syndrome is the result of chemical decay and produces "buckling and shrinking, embrittlement, and bubbling". Redox blemishes are yellow, orange, red, or spots 15-150 micrometres in diameter created by oxidative attacks on the film, and are largely due to poor storage conditions.

Uses

Systems that mount microfilm images in punched cards have been widely used for archival storage of engineering information.

For example, when airlines demand archival engineering drawings to support purchased equipment (in case the vendor goes out of business), (as of 1999) they normally specified punch-card-mounted microfilm with an industry-standard indexing system punched into the card. This permits automated reproduction, as well as permitting mechanical card-sorting equipment to sort and select microfilm drawings.

Aperture card mounted microfilm is roughly 3% of the size and space of conventional paper or vellum engineering drawings. Some military contracts around 1980 began to specify digital storage of engineering and maintenance data because the expenses were even lower than microfilm, but these programs are now finding it difficult to purchase new readers for the old formats.

Microfilm first saw military use during the Franco-Prussian War of 1870–71. During the Siege of Paris, the only way for the provincial government in Tours to communicate with Paris was by pigeon post, and, as the pigeons could not carry paper dispatches, the Tours government turned to microfilm. Using a microphotography unit evacuated from Paris before the siege, clerks in Tours photograped paper dispatches and compressed them to microfilm, which were carried by homing pigeons into Paris and projected by magic lantern while clerks copied the dispatches onto paper.

Libraries began using microfilm in the early 1900s as a preservation strategy for their deteriorating newspaper collections. Books and newspapers that were deemed in danger of decay could be preserved on film and thus access and use could be increased. Microfilming was also a space-saving measure. In his 1945 book, “The Scholar and the Future of the Research Library,” Fremont Rider calculated that research libraries were doubling in space every sixteen years. His suggested solution was microfilming, specifically with his invention, the microcard. Once items were put onto film, they could be removed from circulation and additional shelf space would be made available for rapidly expanding collections. The microcard was superseded by microfiche. By the 1980s, microfilming had become standard policy

Advantages

The medium has numerous advantages:

  • It is compact, with far smaller storage costs than paper documents. Normally 98 document size pages fit on one fiche, reducing to about 0.25% original material. When compared to filing paper, microforms can reduce space storage requirements by up to 95%.
  • It is cheaper to distribute than paper copy. Most microfiche services get a bulk discount on reproduction rights, and have lower reproduction and carriage costs than a comparable amount of printed paper.
  • It is a stable archival form when properly processed. Preservation standard microfilms use wet-processed silver halide dyes in hard gelatin emulsion on a polyester base. With appropriate storage conditions, this film has a life expectancy of 500 years. Unfortunately, in tropical climates with high humidity, fungus eats the gelatin used to bind the silver halide. Thus, diazo-based systems with lower archival lives (20 years) which have polyester or epoxy surfaces are used.
  • Since it is analog (an actual image of the original data), it is easy to view. Unlike digital media, the format requires no software to decode the data stored thereon -- it is instantly comprehensible to persons literate in the language; the only equipment that is needed is a simple magnifying glass. This reduces the possibility of obsolescence.

Disadvantages

  • The principal disadvantage of microforms is that the image is too small to read with the naked eye. Libraries must use special readers that project full-size images on a ground-glass screen.
  • Reader machines used to view microfilm are often difficult to use, requiring the user to carefully wind and rewind until they have arrived at the point where the data they are looking for is stored. Also, photographic illustrations reproduce poorly in microform format, with the image usually not being as sharp as the original. The last problem with the machines is that printers are not always available, limiting the user's ability to make copies for their own purposes.
  • Color microfilm is extremely expensive, thus discouraging most libraries wishing to use microfilm from having color material available. This results in the loss of some information, as color materials will be preserved using regular microfilm in order to save money.
  • When stored in the highest-density drawers, it is easy to misfile a fiche, which is thereafter unavailable. Some libraries therefore keep the microfiche cabinet in a restricted area, and retrieve fiches on demand. Some fiche services use lower-density drawers with labelled pockets for each card.
  • A conventional photocopier cannot reproduce the images. Libraries using microfiche often have a few viewers that can produce a photocopy of an image, for a nominal fee.
  • Like all analog media formats, microfiche is lacking in features taken for granted by users of digital media. Analog copies degrade with each generation, while digital copies have much higher copying fidelity. Digital data can also be indexed and searched easily.

Readers and printers

Desktop readers are boxes with a translucent screen at the front on to which is projected an image from a microform. They have suitable fittings for whatever microform is in use. They may offer a choice of magnifications. They often have powered movement of roll film. When coding blips are recorded on the film a reader is used that can read the blips to find any required image.

Portable readers are plastic devices that fold for carrying, when open they project an image from microfiche on to a reflective screen.

A microfilm printer contains a xerographic copying process, like a photocopier. The image to be printed is projected with synchronised movement on to the drum. These devices offer either small image preview for the operator or full size image preview, when it is called a reader printer. Microform printers usually accept positive or negative films, to give positive images on paper.

Newer readers allow the user to scan a microform image and save it as a digital file.

Media

Flat film : 105 x 148 mm flat film is used for micro images of very large engineering drawings. These may carry a title photographed or written along one edge. Typical reduction is about 20, representing a drawing that is 2.00 x 2.80 metres, that is 79 x 110 in. These films are stored as microfiche. Microfilm : 16 mm or 35 mm film to motion picture standard is used, usually unperforated. Roll microfilm is stored on open reels or put into cassettes. The standard length for using roll film is 30.48 m (100 ft). One roll of 35 mm film may carry 600 images of large engineering drawings or 800 images of broadsheet newspaper pages. 16 mm film may carry 2,400 images of letter sized images as a single stream of micro images along the film set so that lines of text are parallel to the sides of the film or 10,000 small documents, perhaps cheques or betting slips, with both sides of the originals set side by side on the film. Aperture cards : Aperture cards are Hollerith cards into which a hole has been cut. A 35 mm microfilm chip is mounted in the hole inside of a clear plastic sleeve, or secured over the aperture by an adhesive tape. They are used for engineering drawings, for all engineering disciplines. There are libraries of these containing over 3 million cards. Aperture cards may be stored in drawers or in freestanding rotary units. Microfiche : A microfiche is a flat film 105 x 148 mm in size, that is ISO A6. It carries a matrix of micro images. All microfiche are read with text parallel to the long side of the fiche. Frames may be landscape or portrait. Along the top of the fiche a title may be recorded for visual identification. The most commonly used format is a portrait image of about 10 x 14 mm. Office size size papers or magazine pages require a reduction of 24 or 25. Microfiche are stored in open top envelopes which are put in drawers or boxes as file cards, or fitted into pockets in purpose made books.

Image creation

To create microform media, a planetary camera is mounted with vertical axis above a copy that is stationary during exposure. A flow camera moves copy smoothly through the camera to expose film which moves with the reduced image. Alternatively, it may be produced by computers, i.e. COM (computer output microfilm).

Film

Normally microfilming uses high resolution panchromatic high resolution monochrome stock. Positive color film giving good reproduction and high resolution can also be used. Roll film is provided 16, 35 and 105 mm wide in lengths of 30 metres (100 ft) and longer, and is usually unperforated. Roll film is developed, fixed and washed by continuous processors.

Sheet film is supplied in ISO A6 size. This is either processed by hand or using a dental X-ray processor. Camera film is supplied ready mounted in aperture cards. Aperture cards are developed, fixed and washed immediately after exposure by equipment fitted to the camera.

Cameras

Flat film The simplest microfilm camera that is still in use is a rail mounted structure at the top of which is a bellows camera for 105 x 148 mm film. A frame or copy board holds the original drawing vertical. The camera has a horizontal axis which passes through the centre of the copy. The structure may be moved horizontally on rails.

In a darkroom a single film may be inserted into a dark slide or the camera may be fitted with a roll film holder which after an exposure advances the film into a box and cuts the frame off the roll for processing as a single film.Roll film For engineering drawings a freestanding open steel structure is often provided. A camera may be moved vertically on a track. Drawings are placed on a large table for filming, with centres under the lens. Fixed lights illuminate the copy. These cameras are often over 3 metres (10 feet) high. These cameras accept roll film stock of 35 or 16 mm.

For office documents a similar design may be used but bench standing. This is a smaller version of the camera described above. These are provided either with the choice of 16 or 35 mm film or accepting 16 mm film only. Non adjustable versions of the office camera are provided. These have a rigid frame or an enveloping box that holds a camera at a fixed position over a copy board. If this is to work at more than one reduction ratio there are a choice of lenses.

Some cameras expose a pattern of light, referred to as blips, to digitally identify each adjacent frame. This pattern is copied whenever the film is copied for searching.Flow roll film cameras A camera is built into a box. In some versions this is for bench top use, other versions are portable. The operator maintains a stack of material to be filmed in a tray, the camera automatically takes one document after another for advancement through the machine. The camera lens sees the documents as they pass a slot. Film behind the lens advances exactly with the image.

Special purpose flow cameras film both sides of documents, putting both images side by side on 16 mm film. These cameras are used to record cheques and betting slips.Microfiche camera All microfiche cameras are planetary with a step and repeat mechanism to advance the film after each exposure. The simpler versions use a dark slide loaded by the operator in a dark room; after exposure the film is individually processed, which may be by hand or using a dental X-ray processor. Cameras for high output are loaded with a roll of 105 mm film. The exposed film is developed as a roll; this is sometimes cut to individual fiche after processing or kept in roll form for duplication.Computer Output Microfilm

Equipment is available that accepts a data stream from a mainframe computer. This exposes film to produce images as if the stream had been sent to a line printer and the listing had been microfilmed. Because of the source one run may represent many thousands of pages.

Within the equipment character images are made by a light source, this is the negative of text on paper. COM is sometimes processed normally. Other applications require that image appears as a conventional negative; the film is then reversal processed. This outputs either 16 mm film or fiche pages on a 105 mm roll.

Because listing characters are a simple design, a reduction ratio of 50 gives good quality and puts about 300 pages on a microfiche. A microfilm plotter, sometimes called an aperture card plotter, accepts a stream that might be sent to a computer pen plotter. It produces corresponding frames of microfilm. These produce microfilm as 35 or 16 mm film or aperture cards.

Duplication

All regular microfilm copying involves contact exposure under pressure. Then the film is processed to provide a permanent image. Hand copying of a single fiche or aperture card involves exposure over a light box and then individually processing the film. Roll films are contact exposed round a glass cylinder containing a lamp. Processing may be in the same machine or separately.

Silver halide film is a slow version of camera film with a robust top coat. It is suitable for prints or for use as an intermediate from which further prints may be produced. The result is a negative copy. Preservation standards require a master negative, a duplicate negative, and a service copy (positive). Master negatives are kept in deep storage, and duplicate negatives are used to create service copies, which are the copies available to researchers. This multi-generational structure ensures the preservation of the master negative.

Diazo-sensitised film for dye coupling in ammonia gives blue or black dye positive copies. The black image film can be used for further copying.

Vesicular film is sensitised with a diazo dye, which after exposure is developed by heat. Where light has come to the film remains clear, in the areas under the dark image the diazo compound is destroyed quickly, releasing millions of minute bubbles of nitrogen into the film. This produces an image that diffuses light. It produces a good black appearance in a reader, but it cannot be used for further copying.

Format conversion

These conversions may be applied to camera output or to release copies. Single microfiche are cut from rolls of 105 mm film. A bench top device is available that enables an operator to cut exposed frames of roll film and fit these into ready made aperture cards.

Transparent jackets are made A5 size each with 6 pockets into which strips of 16 mm film may be inserted, so creating microfiche. Equipment allows an operator to insert strips from a roll of film. This is particularly useful as frames may be added to a fiche at any time. The pockets are made using a thin film so that duplicates may be made from the assembled fiche.

Digital conversion

Another type of conversion is microform to digital. This is done using an optical scanner that projects the film onto a CCD array and captures it in a raw digital format. Since the different types of microform are dissimilar in shape and size, the scanners are usually able to handle only one type. However, there are some that have the possibility of swapping modules for the different microform types. Software (normally on the scanner itself) is then used to convert the raw capture into a standard image format for archival.

The physical condition of microfilm greatly impacts the quality of the digitized copy. Microfilm with a cellulose acetate base (popular through the 1970s) is frequently subject to vinegar syndrome, redox blemishes, and tears, and even preservation standard silver halide film on a polyester base can be subject to silvering and degradation of the emulsion -- all issues which affect the quality of the scanned image.

Digitizing microfilm can be inexpensive when automated scanners are employed. The Utah Digital Newspapers Program has found that, with automated equipment, scanning can be performed at $0.15 per page.

For the resulting files to be useful, they must be organized in some way. This can be accomplished in a variety of different ways, dependent on the source media and the desired usage. In this regard, aperture cards with Hollerith information are probably the easiest since image data can be extracted from the card itself if the scanner supports it. Some types of microfilm will contain a counter next to the images, these can be referenced to an already existing database. Other microfilm reels will have a 'blip' system: small marks next to the images of varying lengths used to indicate document hierarchy (longest: root, long: branch, short: leaf). If the scanner is able to capture and process these then the image files can be arranged in the same manner. Optical character recognition is also frequently employed to provide automated full-text searchable files. Common issues that affect the accuracy of OCR applied to scanned images of microfilm include unusual fonts, faded printing, shaded backgrounds, fragmented letters, skewed text, curved lines and bleed through on the originals. For film types with no distinguishing marks, or when OCR is impossible (handwriting, layout issues, degraded text), the data must be entered in manually - a very time consuming process.

References

  • Jamison, M. (1988). The microcard: Fremont Rider's precomputer revolution. Libraries & Culture, 23, 1-17.
  • Metcalf, K. D. (1996). Implications of microfilm and microprint for libraries [originally published in September 1, 1945]. Library Journal (1976), 121, S5.
  • Molyneux, R. E. (1994). What did rider do? An inquiry into the methodology of Fremont Rider's the scholar and the future of the research library. Libraries & Culture, 29, 297-325.
  • Rider, F. (1944). The scholar and the future of the research library. New York: Hadham Press.

See also

External links

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