An aperture card is two records fused into one piece of stock: a standard punched card carrying printed and machine-readable index data, with a single frame of 35mm microfilm mounted in a window cut into the card. For decades, they were the standard medium for storing engineering drawings, and organizations across aerospace, defense, utilities, manufacturing, and government still hold vaults of them today — not out of nostalgia, but because those cards are frequently the only surviving as-built record of a facility, a part, or a system that is still in operation. A pump station built in 1974 does not stop needing its drawings just because the medium they are stored on has gone obsolete. Converting those cards to digital files is not a modernization project so much as a continuity project: keeping an active engineering record accessible to people who no longer have a way to read the original.

What Is Actually On an Aperture Card

Scanning an aperture card correctly means capturing two different kinds of information, not one. The film chip holds the drawing itself — the actual engineering content. The card stock around it carries the index: a printed line of human-readable text along the top edge, and, on most cards, a pattern of punched holes encoding the same information in machine-readable form, following the Hollerith punch conventions that the IBM card format was originally built on. A vendor that scans the film chip and ignores the card data has only done half the job. The image exists, but it is not findable — and an unfindable engineering drawing is functionally the same as one that was never converted at all.

The Hollerith Data, and Why Getting It Right Matters

The punched and printed data on an aperture card typically encodes fields like drawing number, revision letter, sheet size, sheet number, and often a CAGE code or department identifier — the exact field layout depends on the standard your organization or your original engineering department used. Typical fields captured include drawing number, revision, sheet size and date, adjusted per your requirements.

That data is what turns a folder of scanned images into a searchable engineering archive. We capture it by reading the punch pattern and the printed index line together, cross-checking the two against each other rather than trusting either alone, because a card with a chipped corner or a partially unreadable punch column is common enough after decades in storage that single-source indexing is not good enough for engineering records people will actually rely on. The result is a delivered index — as a database or spreadsheet, or loaded directly into your document management or engineering records system — that lets an engineer pull the right drawing by number or revision instead of paging through thousands of images by hand.

Damaged and Degraded Film Chips: Where the Film Lab Matters Most

This is the part of aperture card conversion that separates a real digitization partner from a vendor with a scanner. Most aperture card collections are not in the condition they were in when they were filmed. Chips scratch. Mylar-base film warps under decades of temperature and humidity swings in a records vault that was never climate-controlled the way it should have been. Older duplicate stock — diazo and vesicular film used heavily for working-copy duplicates in the mid-twentieth century — fades, discolors, or degrades chemically in ways the original silver-halide master never did. Cards get stuck to each other. Chips pick up dirt, fingerprints, and mold. Run any of that through a scanner without treatment first and you get exactly what you would expect: a perfectly captured image of an illegible drawing.

DMI operates a working film laboratory — a capability almost no competitor in this space still maintains. Damaged, scratched, warped, or poorly duplicated film chips are chemically remediated at the lab before they are scanned, not after. That means cleaning, addressing physical damage and warping, and treating problem duplicate stock so the scan captures a usable, legible image of the actual drawing rather than a faithful digital copy of a problem that has been sitting in your vault for forty years. On a collection where a meaningful percentage of the chips are degraded — which is common on anything filmed before the 1980s — this single capability is often the difference between a conversion project that produces a usable archive and one that produces a pile of unreadable files you still cannot use. Because film requires lab equipment to remediate and scan correctly, aperture card conversion is performed at DMI’s facility rather than on-site; on-site capture is reserved for paper originals, which do not carry this risk.

How Aperture Card Scanning Works

Each card is processed as a single unit — the film chip and its index data captured together and linked in the delivered file set, so the image and its metadata never come apart during production or after. The film chip is imaged on microfilm capture equipment sized for aperture card work. Film images are generally captured in full greyscale at 300 DPI, although other resolutions and bit depths are available. The card’s printed index line is captured optically, and the punched Hollerith data is read directly, with the two checked against each other as described above. Quality control on engineering drawings is not optional — a mis-keyed revision letter can send an engineer to the wrong version of a drawing — so indexed data is verified before a batch is considered complete.

Output Formats and CAD-Adjacent Use

Aperture card conversions are typically delivered as raster images — single-page or multi-page TIFF, and PDF or PDF/A where a long-term archival format is required — paired with the extracted index data as a structured file (CSV or database export) or loaded directly into a target document management, engineering records, or PLM system. For organizations working in a CAD environment, the delivered raster image commonly serves as an as-built reference layer or attachment linked to the current drawing record, even where the drawing itself has not been redrawn as a native CAD file. Where a fully editable vector drawing is the goal rather than a reference image, that is a separate conversion step from the scan itself — worth discussing up front if that is the end state you need.

How a Project Is Scoped and Shipped

Every aperture card project starts with an honest look at what is actually in the boxes: approximate card count, condition, and how much of the collection shows signs of film damage or degraded duplicate stock, since that materially affects both timeline and whether remediation work is needed before scanning can even start. From there we agree on the index fields to be captured, the delivery format, and how the finished files should be structured or loaded. Cards typically travel to DMI’s facility for processing, are processed in tracked batches, and are delivered as agreed. Because these are frequently the only surviving record of an active drawing, chain of custody is tracked through the process rather than treated as an afterthought.

What Happens to the Cards After Scanning

Once a card has been imaged and its index verified, what happens to the physical original is your call, not ours. Depending on your organization’s retention policy and any regulatory requirements attached to the records, cards can be returned to you, held in secure storage, or destroyed with documentation confirming it was done. DMI will hold documents in our secure film vault prior to post-project disposition and, if destroyed, will produce a Certificate of Destruction for your records. Many engineering and government records programs have a formal retention schedule that dictates this already; we work to whatever that schedule requires rather than assuming.

Request a Quote

Aperture card collections vary enormously in size, condition, and index complexity, so DMI does not publish flat rates — every project is quoted after we understand what you actually have, including how much of it may need film remediation before it can be scanned at all. If you are managing an engineering archive, a facilities records program, or a government collection still sitting on aperture cards, tell us about your collection and we will scope it properly.

Request a quote for aperture card scanning from Data Management Internationale, or call 1-800-DMI-4210. Collections that include aperture cards usually include other film too — see microfilm scanning, wide format scanning for the oversized drawings that were never filmed, and OCR services if the delivered index needs to be full-text searchable.