The lens distortion database shipped as `lens-db.json`
======================================================

WHAT IT IS

`lens-db.json` is a derived work of the Lensfun lens database: 1520 lenses and
6430 distortion calibrations, measured against test charts by the people who own
the lenses. It was produced from the XML files under `data/db/` of the Lensfun
source distribution by keeping, for every lens that carries at least one
distortion calibration, its model name, maker, crop factor, aspect ratio, and
the distortion model and coefficients at each calibrated focal length. No
coefficient was altered, refitted or interpolated; the only changes are of
format — the field names are abbreviated and the numbers are rounded to seven
decimal places, which is well below the precision of any of the measurements.

Vignetting, chromatic aberration, mount and camera records were dropped because
this product does not use them.

SOURCE

    Lensfun — https://lensfun.github.io/
    Repository — https://github.com/lensfun/lensfun

LICENCE

The Lensfun DATABASE is licensed under the Creative Commons
Attribution-Share Alike 3.0 licence (CC BY-SA 3.0). The Lensfun LIBRARY is
LGPL-3 and is NOT used here — no Lensfun code is shipped, linked or copied into
this site; the distortion models were reimplemented from the published formulas.

    https://creativecommons.org/licenses/by-sa/3.0/

Because `lens-db.json` is a derived work of that database, it is distributed
under the same licence: CC BY-SA 3.0, attributed to the Lensfun project and its
contributors. Anyone may take `lens-db.json` from this site and use it under
those terms.

WHAT SHARE-ALIKE DOES AND DOES NOT REACH

It reaches this data file and any further derivative of it. It does not reach
the code that reads it: `src/engine/lens-models.js` implements the PTLens,
Poly3 and Poly5 polynomials from their published mathematical definitions, which
are not themselves copyrightable, and `src/engine/lens-match.js` contains no
Lensfun code. That is the same separation Darktable and RawTherapee rely on when
they ship the database beside their own readers.

REGENERATING IT

The extraction is mechanical and reproducible from a Lensfun checkout. If the
database is refreshed, this file must be refreshed with it, including the lens
and calibration counts above — a stale attribution is a false statement about
what is being distributed.