Re: Lens correction database

> -----Message d'origine-----
> De : hugin-ptx@...
> [mailto:hugin-ptx@...] De la part de Pablo d'Angelo
> Envoyé : vendredi 11 mai 2007 00:49
> À : create@...; hugin and other free
> panoramic software
> Cc : michel thoby; sandersn@...
> Objet : [hugin-ptx] Lens correction database
>
>
> Hi together
>
> Some people who have attended my talk about hugin at the LGM
> might remember that I proposed to build a database of lens
> correction coefficients, that can be used by open source
> software (such as ufraw, gimp, krita, digikam, f-spot, etc)
> to automatically correct for lens "defects" such as lens
> distortion, vignetting and even transverse chromatic abberation.
>
> The slides for my LGM talk are available at:
> http://hugin.sf.net/tech/LGM_2007.pdf
>
> At least the Krita people are interested in such functionality:
> http://www.valdyas.org/fading/index.cgi/2007/05/08#hugin
>
> I plan to write a lightweight C library that contain the main
> pieces of code required to apply the corrections and use the
> proposed database.
>
>
> Current situation:
>
> Several databases and associated programs for correcting lens
> defects exist.
>
> For example PTLens uses a database with lens distortions
> coefficients.
> Unfortunately, Its author, Thomas Niemann has decided to
> close and encrypt
> the underlaying database a bit more than one year ago,
> shortly after I wrote
> "fulla", a command line tool to correct lens distortion.
> fulla can use the
> old, unencrypted PTLens database and correct distortions in images
> automatically. Note that PTLens requires manual user
> interaction for other
> corrections (vignetting, chromatic abberation).
> http://epaperpress.com/ptlens/
>
> In a sense the proposed database is a free alternative to the PTLens
> database, but additionally can include coefficients for
> automatic correction
> of vignetting and chromatic abberations.
>
> DxO is a commercial software that can correct the mentioned
> defects and even
> more. Obviously their database and correction methods are not
> available.
> http://www.dxo.com
>
>
> Proposed solution:
> ==================
>
> Before that can happen, we need to agree on a database format
> that can
> include all required parameters. This specifically includes:
>
> During the panorama stitching process, hugin is required to
> correct these
> distortions, and can thus be used for estimation of the
> calibration parameters.
>
> The idea is that people who want to correct their lens take
> some test shots,
> and use hugin to estimate the required calibration
> parameters. These are
> then sent (hugin projects and original images) to a lens database
> coordinator, where they are checked for plausibility and
> incorporated into
> the database.
>
>
> Scope of database:
>
> 1. Distortion correction:
> radial distortion, same as PTLens, 3 parameter radial
> polynmial, described
> in detail at: http://wiki.panotools.org/Lens_correction_model
> Varies mainly with focal length. Parameters can be estimated
> at several
> focal lengths and interpolated in between. Each focal length
> requires a
> single image for calibration.
>
> 2. Vignetting correction:
> radial correction, radial vignetting correction by division:
> I = I / (1 + b*r^2 + c*r^4 + d*r^6)
> The parameters vary with both focal length and aperture.
> Each focal length and aperture setting require 2 or 3 images for
> calibration.
>
> 3. Chromatic abberations:
> Individual distortion correction of red and blue channel, parameters
> can be estimated using hugin (more work than the other
> approaches), or by
> trial and error. Most lenses require just a single scaling factor.
> Mainly depends on focal length.
>
> Instructions for estimating the respective parameters with
> hugin are in
> the works.
>
> Who would be interested in using and building such a database?
>
> License:
>
> What kind of license should be used (for the code and more
> important, the
> database)? A GPL like license to restrict usage to open
> source software or a
> LGPL like license? Or a non-commercial license? Can code
> licences be applied
> to databases?
>
>
>
> Database (XML) layout:
>
> For each camera and lens, a single entry would be required.
> Note that my XML skills are seriously lacking, so any comments
> with respect to a different xml syntax are appreciated.
>
> Camera description:
> ===================
>
> <!-- name of the camera, crop factor -->
> <camera make="Canon" name="EOS 300D" cropfactor="1.6">
>
>   <!-- exif data required for recognition of the camera -->
>   <exif make="Canon" model="Canon EOS 300D DIGITAL"/>
>
>   <!-- mount of the camera (used to identify matching lenses) -->
>   <mount>canonSLR</mount>
>   <mount>canonEfsSLR</mount>
>   <mount>genericSLR</mount>
>
>   <!-- a free from text field for misc annotations -->
>   <comment>Any annotation</comment>
> </camera>
>
>
> Description of a lens:
> ======================
>
> <lens name="Canon EF-S 10-22mm f/3.5-4.5 USM"
>        minfocallength="10" maxfocallength="22"
>        maxaperture="3.5"
>        <!-- type of lens, either rectilinear or fisheye -->
>        type="rectilinear">
>
>   <!-- person calibrating the lens -->
>   <author>Author</author>
>
>   <!-- mount(s) of a lens (ie. the type of cameras it can be
> mounted on) -->
>   <mount>canonEfsSLR</mount>
>
>   <!-- a rating (quality control passed or not) -->
>   <rating>1</rating>
>
>   <!-- serial number range (for lenses with same name but different
> properties, not required) -->
>   <serial number="300" min="1" max="1000">
>
>   <!-- arbitrary user comment -->
>   <comment></comment>
>
>   <!-- correction coefficients for each focal length
>   <calibration focallength="10">
>
>       <!-- radial distortion correction, as in PTLens -->
>       <distortion a="0.02" b="-0.012" c="0">
>       <!-- transverse chromatic abberation correction -->
>       <tcaRed a="0" b="0" c="0" d="0">
>       <tcaBlue a="0" b="0" c="0" d="0">
>
>
>       <!-- aperture specific calibration values (vignetting) -->
>       <calibration aperture="3.5">
>         <vignetting b="-0.1" c="-0.2 d="0">
>       </calibration>
>
>       <calibration aperture="8">
>         <vignetting b="-0.1" c="-0.2 d="-0.3">
>       </calibration>
>
>       <calibration aperture="22">
>         <vignetting b="-0.1" c="-0.2 d="0">
>       </calibration>
>   </calibration>
>
>   <calibration focallength="14">
>       <distortion a="0.003" b="-0.001" c="0">
>       <tcaRed a="0" b="0" c="0" d="0">
>       <tcaBlue a="0" b="0" c="0" d="0">
>
>       <calibration aperture="4">
>         <vignetting b="-0.1" c="-0.2 d="0">
>       </calibration>
>       <calibration aperture="8">
>         <vignetting b="-0.1" c="-0.2 d="-0.3">
>       </calibration>
>       <calibration aperture="22">
>         <vignetting b="-0.1" c="-0.2 d="0">
>       </calibration>
>   </calibration>
>   <calibration focallength="22">
>       <!-- some more data -->
>   </calibration>
>
> </lens>
>
>
> Any feedback appreciated. Please continue discussion on the
> CREATE mailing list.
>
> ciao
>    Pablo
>
> >
>