Identify one-up and two-up microfilm layouts

Simplex and duplex: the direct definition

Simplex microfilm places one page image at a time, often called one-up. Duplex microfilm places two page images at a time, often called two-up. Missouri State Archives preservation guidance uses these meanings for simplex IA or IB and duplex IIA or IIB positions.

This is a filming-layout distinction, not a paper scanner setting for front-and-back capture. It also does not identify a reel versus cartridge, 16 mm versus 35 mm width, positive versus negative polarity, reduction ratio, emulsion, base, or film generation. Those are separate dimensions to record at intake.

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Identify the layout from the filmed images

Inspect several consecutive recorded image areas in a compatible reader or a representative scan. A simplex sequence presents one page image in each image area. A duplex sequence presents two page images together in one image area, sometimes as facing leaves with a visible central gutter. Confirm the pattern across more than one frame; an isolated target, duplicate exposure, or irregular record should not define the whole roll.

Read orientation separately. Cine places text perpendicular to the length of the film, while comic places text parallel to it. Either orientation can be simplex or duplex. Likewise, positive, negative, or mixed polarity changes tonal appearance but does not change a one-up layout into a two-up layout. Image marks or blips are optical navigation marks, not pages and not proof of document boundaries.

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What a two-up frame can represent

Duplex filming can preserve two open leaves in one exposure. In the Missouri program guidance, a two-up exception was contemplated for records in which two facing leaves make up one document, including some indexes and tax records. That is a documented use case, not a rule that every duplex frame represents a single two-page record.

A two-up image may instead contain adjacent but independent pages, and a roll can include targets, blanks, retakes, or layout changes. Preserve the source sequence and inspect a sample before deciding whether a paired image should remain a spread, be divided into two access images, or receive a special exception rule. Duplex does not imply a particular carrier, width, or film chemistry.

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Capture and quality issues to review

A two-up layout adds a page-boundary decision to capture review: the project needs to determine whether both pages are retained together or separated without clipping document content. Check the center gutter, page edges, skew, focus, density variation, page spacing, and any changes in reduction or orientation. Missouri guidance notes that skew and changing reductions can complicate digitization, while Library of Congress guidance identifies focus, density, and reduction as factors that affect OCR and usable image quality.

Capture the full content of the microfilm frame before defining an access derivative. FADGI explains that microfilm is digitized at a known PPI relative to the film, not automatically to the original paper size, and that known reduction should be recorded in metadata. Older or variably filmed material may support reasonable legibility rather than reproduction-quality files, so a representative sample is more informative than a universal scanner setting.

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Decide indexing, OCR, and output at the right level

Keep a source reference even if a duplex frame is separated for access. A useful index can retain the roll or reel identifier, original frame reference, layout, and a left/right or page-order relationship when applicable. The delivery choice can then be a single two-page image, two linked page images, or another approved representation. The source image remains the evidence for the decision.

Illustrative indexing example — no PII: Reel R-012, original film frame 00438, contains source pages 146 and 147. A spread-preserving output can use one frame record, while split outputs can use two page records linked to original frame 00438 and labeled page order 1 and 2. OCR may support searching printed text, but it does not establish the correct boundary or guarantee every character; retain structured fields for identifiers that must be retrieved consistently.

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Prepare without alteration and ask focused sample questions

Keep the reel, box labels, targets, and existing order together. Handle microfilm by its edges with gloves, keep equipment and work surfaces clean, and note visible condition issues rather than attempting repairs. Do not remove film from a cartridge to identify a layout, and do not infer the film base or chemistry from its age or color. National Archives guidance recommends preservation-specialist input for deteriorated material, damaged film, or cartridges that need removal for access.

For a sample review, ask: Do all selected frames show the same one-up or two-up pattern? Do paired images represent facing leaves or separate records? Should the approved output retain spreads or split pages? Which roll, target, blip, or visible page reference must remain in the index? What small text, faint areas, folds, or density changes should be included in the test? National Microfilm reviews representative samples to help define scanning, indexing, OCR, and approved delivery scope.

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Common questions