Howto for lensfun calibration script "lens_calibrate.py"

Howto and notes for using lens_calibrate.py for lensfun

GitHub Project: https://github.com/lensfun/lensfun GitHub Page: https://lensfun.github.io/

See Andreas Schneider’s tutorial and python scripts: https://pixls.us/articles/create-lens-calibration-data-for-lensfun/

Original python program lens_calibrate.py: https://gitlab.com/cryptomilk/lens_calibrate

Setting up Python environment (Ubuntu 22.04, 24.04)

• install darktable, hugin, imagemagick (convert) and gnuplot

$ sudo apt-get install python3-pip python3-venv
$ sudo apt-get install build-essential python3-all-dev libexiv2-dev libboost-python-dev

$ python3 -m venv .venv
$ source .venv/bin/activate
$ python3 -m pip install --upgrade pip
$ python3 -m pip install -r requirements.txt

Running lens_calibrate.py

$ source .venv/bin/activate

$ ./lens_calibrate init

$ ./lens_calibrate distortion

$ ./lens_calibrate --complex-tca tca

$ ./lens_calibrate vignetting

$ ./lens_calibrate generate_xml

Contributing your lensfun.xml

To contribute your calibration data data for your lens to the lensfun project, execute the script with the following command:

$ ./lens_calibrate ship
Created lensfun_calibration.tar.gz
Open a bug at https://github.com/lensfun/lensfun/issues/ with the data.

This will create a tarball with all the required data. Now go to https://github.com/lensfun/lensfun/issues/ and open a bug (New issue) using the following subject:

Calibration data for <lens model>

And for the description just use:

Please add the attached lens data to the lensfun data base.

Attach the lensfun_calibration.tar.gz to the bugreport.

Upload verification images using the calibration service upload server and refer to issue: https://wilson.bronger.org/calibration

Vignetting and Panasonic Lumix camera's

Lumix camera's output 2 different raw files, depending on the camera setting "vignetting compensation" (menu "VIGNETTING.COMP"). When the vignetting compensation setting is OFF, the raw file is a more pure raw file. When the vignetting compensation setting is ON, the camera applies some sort of vignetting compensation to the raw file. Lumix L-mount and MFT camera's default to VIGNETTING.COMP set to ON, but the user can change it in the menu. The camera stores the vignetting compensation setting in an exif tag "Shading Compensation" in the raw file. E.g. exiftool can read the tag "Shading Compensation".

Lensfun is intended for correcting pure raw images. So all (most?) calibration data in its database are done with vignetting compensation OFF. When applying the default calibration profile to an image that has been shot with vignetting compensation ON, the corners will be too bright (like over compensation). For those images a different calibration profile is needed, that takes into account the in camera processing that is already in the image.

In summary: 1 lens, 1 camera, 1 setting ON or OFF -> 2 different raw files -> 2 different profiles

The lensfun database must contain unique lens names.

Solution: create 2 different profile names, e.g.

<model>my lens</model>
<model>my lens ShadingCompensation On</model>

In darktable, both lenses show up in the menu. The first profile will be selected by default. From the menu the other profile can be selected.

Exiftool command to determine vignetting compensation mode from raw file

exiftool -shadingcompensation *.RW2