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To apply FADGI, pick a target star level appropriate to the material, capture an objective device-level target in your production setup, and analyse it with conformance software (OpenDICE, DCEval or Imatest) that reports every metric against the star tolerances. FADGI's Technical Guidelines for Digitizing Cultural Heritage Materials turn vague notions of "good quality" into measurable, pass/fail performance metrics, so your collection stays consistent and your claims are documented and defensible.
What exactly does FADGI specify?
FADGI defines performance for a set of imaging properties and assigns each a tolerance per star level. The headline metrics are:
- Tone response (OECF) — how greys map from original to file
- Colour accuracy — mean and maximum
ΔE2000against a reference chart - Spatial resolution / MTF — sampling efficiency and limiting resolution
- Noise — at defined patch densities
- Uniformity — illumination evenness and colour shading across the frame
- Sharpening and artefacts — over-sharpening halos are penalised
Crucially these are device-level metrics: you measure the system, not subjectively judge a picture.
How do I choose a star level?
Match the star to the value and detail of the originals, and to budget.
| Star | Typical use | Effort |
|---|---|---|
| 1 star | Quick informational captures, finding aids | Low |
| 2 star | General access, bulk runs, born-analogue text | Moderate |
| 3 star | Strong production master target for most archives | High |
| 4 star | Rare, high-value, fine-detail originals | Very high |
Most production programmes settle on 3-star as the master target and accept 2-star for high-volume routine material. Stating the star level per collection in your imaging policy is itself good practice.
How do I measure FADGI compliance step by step?
The workflow is repeatable per session:
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1. Mount an objective target (Golden Thread / device-level) in the capture plane.
2. Capture it under production lighting, lens, aperture and distance.
3. Convert the raw to TIFF exactly as you would a real object.
4. Run conformance software against the target's reference data.
5. Read the per-metric report and the overall star result.
6. Adjust (focus, light evenness, sharpening) and re-shoot if any metric fails.With the free OpenDICE / DCEval tooling the analysis is one command-like operation:
bash
# Conceptual conformance run
dceval --image golden_thread_session.tif \
--target object-level \
--aimpoints fadgi-3star \
--report session_2025-03-08.csv
# -> Tone: PASS Colour dE2000 mean 1.9: PASS MTF50: PASS Noise: WARNHow often should I re-test against FADGI?
Re-shoot and re-analyse the target at the start of every imaging session, after any change to lighting, lens or focus, and at intervals during long runs (for example every 200–500 captures). Save each conformance report alongside the day's images. This running log is what lets you claim compliance across an entire collection, not just one lucky frame.
What are the common reasons captures fail FADGI?
- Uneven illumination — one corner darker than the others fails uniformity; fix lamp angles and distance.
- Over-sharpening — in-camera or raw-processing sharpening creates halos that fail the artefact check. Keep masters minimally sharpened.
- Colour drift — an outdated capture profile pushes
ΔEover tolerance; re-profile. - Focus error — soft focus tanks MTF even at correct resolution; confirm critical focus with live view.
- Wrong target distance — shooting the chart at a different distance than the objects invalidates the result.
How do I document compliance for the record?
Store, per session: the conformance report, the star level claimed, the target used, the equipment and lighting profile, and the operator. Reference the specific FADGI guidelines version in your imaging policy. When an auditor, funder or future curator asks "is this collection FADGI 3-star?", you answer with evidence, not assertion.
Key Takeaways
- FADGI converts image quality into measurable device-level metrics with a 1–4 star scale.
- Choose a star level per collection; 3-star is a common master target, 2-star for bulk runs.
- Measure with an objective target and conformance software (OpenDICE/DCEval free, Imatest commercial).
- Re-test every session and after any setup change; archive each report.
- Watch the usual failures: uniformity, over-sharpening, colour drift, focus.
- FADGI and Metamorfoze are different benchmarks — stars vs pass/fail tiers.
- Document the star level, version and evidence in your imaging policy to make claims defensible.
Frequently Asked Questions
What are the FADGI imaging guidelines?
FADGI (Federal Agencies Digital Guidelines Initiative) publishes the Technical Guidelines for Digitizing Cultural Heritage Materials, defining measurable performance metrics and a 1–4 star rating for image quality. They are the de facto North American benchmark for archival imaging.
What do the FADGI star levels mean?
Stars run 1 to 4: 1-star is informational, 2-star is acceptable for many access purposes, 3-star is a strong production target, and 4-star is the most rigorous, near-reference quality reserved for the most valuable or detailed originals.
How do I measure FADGI compliance?
You shoot an objective target (for example a Golden Thread or ISO 16067-style device-level target) and analyse it with conformance software such as OpenDICE, Imatest, or DCEval, which reports tone, colour ΔE, resolution, noise and uniformity against the star tolerances.
Is FADGI the same as Metamorfoze?
No. Both are objective imaging benchmarks, but Metamorfoze (Dutch) uses pass/fail tiers (Full, Light, Extra Light) while FADGI uses a 1–4 star scale. They measure overlapping properties with different tolerances and terminology.
Do I need expensive software to apply FADGI?
Not necessarily. OpenDICE and the DICE/DCEval tooling are free, and a Golden Thread target plus that software gives you a conformance report. Commercial options like Imatest add depth but are not required to claim a star level.