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Part of Digitizing a family collection costs more after the scanner than before it
Photo digitization at home: resolution and consistency
How the National Archives frames resolution, why consistent settings matter, and what to record when preparing a home photo-scanning workflow.
What to take away
- Resolution means nothing until you say relative to what. Institutional specifications state dpi at the size of the original.
- Consistency across a collection matters more than the highest setting on any one item.
- Buy a flatbed with a transparency unit only if you actually have negatives and slides. Otherwise it is wasted money.
- No scanners are named here. Nothing was tested for this article.
Why no ranked scanner list
A ranked list of machines is not: none were tested, and naming them without testing is guessing. What follows is a way to think about resolution and consistency before choosing equipment.
The settings, and where they come from
The National Archives published a scanning and file format matrix in January 1998 as part of its electronic access work. It is old, and its file format recommendations belong to their decade. Its framing of resolution is still the clearest short statement of the idea.
Archive matrix working figures
- 8-bitgrayscale for everything
- 24-bitcolor for everything
- 300 dpidocuments, higher tier
- 200 dpidocuments, lower tier
Equivalent dpi depends on original
Contact print
- Original size
- Larger
- Same 300 dpi scan
- More detail
- To match detail
- 300 dpi
Negative
- Original size
- Smaller
- Same 300 dpi scan
- Less detail
- To match detail
- Far higher dpi
That scanning and file format matrix specifies that all dots per inch figures are equivalent dpi for the size of the original document. Scanning from photographic intermediates or microfilm should be done at whatever dpi achieves the cited resolution on the original.
That is the sentence to carry away. Scanning a contact print at 300 dpi and scanning the negative it came from at 300 dpi are not the same job. The negative is smaller and needs a far higher setting to reach equivalent detail.
The matrix also shows the second habit worth copying: it fixes bit depth across the whole project. It specifies 8-bit grayscale or 24-bit color for everything, because document legibility is inconsistent and the aim is to image them in a consistent way.
The matrix sets working figures of 300 dpi for documents in its higher tier and 200 dpi in its lower one. For photographs, it calls for adjusting dpi to reach a target pixel dimension rather than prescribing one universal dpi. Choose a target for the intended use of the images, then keep the approach consistent across the collection.
Fix your settings once, write them down, and stop adjusting per item.
The kit
- A flatbed scanner with a lid that lifts clear.Anything with an automatic document feeder is for offices, and a feeder will eventually eat something irreplaceable.
- A transparency unit or a dedicated film scanner, only if you have negatives or slides.
- A soft brush and a blowerfor dust on the platen and on the item.
- Cotton or nitrile glovesfor negatives, which show every fingerprint.
- Two trays, one for unscanned and one for scanned. This is the single cheapest error-prevention tool in the room.
- A written settings notetaped to the wall: resolution, bit depth, file format, color profile, and naming pattern. Save an untouched TIFF master and make JPEG derivatives for sharing. A simple pattern such as
collection_subject_item_master.tifandcollection_subject_item_derivative.jpgkeeps related files together.
Know what you are putting on the glass
Negatives are not one material, and the differences matter before you handle a box of them. The Canadian Conservation Institute's technical bulletin on the care of plastic film-based negative collections covers negatives on cellulose nitrate, cellulose acetate and polyester bases, including composition, deterioration, access, handling and storage.
Its identification sequence is the part to use, because it runs from free to laboratory in five steps. Date the material first. Examine the edge markings. Examine the notch codes. Then, if you still need to know, run a light polarisation test to identify polyester, and a diphenylamine spot test to identify cellulose nitrate.
The first three cost nothing and settle most boxes. The bulletin also covers the health and safety side of degrading plastics: decomposition products, long-term exposure, mold, and handling guidelines. Read it before spending a weekend at a scanner with a box of old negatives open beside you.
What to skip
Skip the automatic feeder, skip built-in dust removal on anything you care about, skip the software's automatic enhancement, and skip scanning at the machine's maximum optical resolution for everything. A collection scanned consistently at a sensible setting is more useful than a third of one scanned magnificently.
Our guide to what digitizing costs after the scanner covers the running cost, and the notes on setting up a scanning station cover the bench itself.
