Microform - Digital Conversion

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. Until recently, since the different types of microform are dissimilar in shape and size, the scanners were usually able to handle only one type of microform at a time. There are some scanners that have the possibility of swapping modules for the different microform types and the latest viewer/scanner can accept any microform (roll, fiche, opaque cards, fiche,and/or aperture cards). Software (normally on the scanner itself, but more recently in an attached PC) 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. Recent additions to the digital scanner field have brought the cost of scanning down substantially so that when large projects are scanned (millions of pages) the price per scan can be pennies.

Modern microform scanners utilize 8 bit gray shade scanning arrays and are thus able to provide quite high quality scans in a wealth of different digital formats (CCITT Group IV which is compressed black & white -bitonal, JPG or JPEG which is gray or color compression, bitmaps which are not compressed, or a number of other (some proprietary) formats such as PDF, LZW, GIF, etc.). These modern scanners are also able to scan at "Archival" resolution up to 600 dpi.

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 (OCR) 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.