Hallöchen! Matt Feifarek writes:
> On Fri, Jan 11, 2013 at 3:59 PM, Pascal de Bruijn > <[email protected]>wrote: > >> To be honest, if this would be implemented, I wonder what would >> happen to Lensfun. Contributions may drop even further, replacing >> free distortion correction with a dependence on the grace of >> Adobe. > > My hope is a converter from the .lcp files to the xml ones that > lensfun needs, not to replace libraries. I wrote such a converter for the distortion part. My plan was to fit the Adobe curve with the LensFun polynomial. It didn't work. I haven't yet had a close look at the mathematics involved (haven't had time for it anymore for the last three months), but my preliminary analysis was that it cannot work: You cannot fit one polynomial with a different one reasonably. Maybe because both are orthogonal? Anyway ... If this turns out to be true, the only way to have a converter is to embed Adobe's models into LensFun. Actually, given the fact that LensFun implements already many models, I don't think this would be very difficult. But I don't have time for it. >> Any particular problem with generating the corrections? > > It's been in finding good images, yes. I've found some contrasty, > rectilinear architecture, but without correction, the images have > lots of chromatic abberation... which makes it hard to find > pin-prick accuracy for the control points. > > The whole hugin process kindof sucks, too. Have you had a look at <http://wilson.homeunix.com/lens_calibration_tutorial/>? >> Typically a lot of the problem is bad source imagery. I had some >> straight lines printed on A2 sized piece of paper and stuck it to >> a sheet of foam-board to keep it perfectly straight. > > I'll try that, good idea. Architecture is unreliable! Modern architecture is okay. The PTLens library relies on it, and its author does it for a living after all. If you want to be absolutely sure, use string+plummet, and take three pictures which you calibrate in one run: One with the string close to the long border, one to the short border, and one parallel to the long border but running closer to the centre of the image. The problem is that distortion parameters may depend on focus distance. I have no study at hand about how frequent and how serious this problem is but I recommend taking pictures at a minimum distance of 8 metres. For example, http://en.wikipedia.org/wiki/Breathing_(lens) magnifies the image which changes the a, b, c parameters because their coordinate system is magnified, too. See also http://www.dxo.com/en/photo/dxo_optics_pro/features/optics_geometry_corrections/distortion#ancre_how_complex point "3. Focus dependence". For wide-angles and fisheyes, night sky calibration may be an option, see <http://www.johnhpanos.com/starcal.htm>. This morning, I took pictures for this, but I haven't yet given the calibration a try. Tschö, Torsten. -- Torsten Bronger Jabber ID: [email protected] or http://bronger-jmp.appspot.com ------------------------------------------------------------------------------ Master Visual Studio, SharePoint, SQL, ASP.NET, C# 2012, HTML5, CSS, MVC, Windows 8 Apps, JavaScript and much more. Keep your skills current with LearnDevNow - 3,200 step-by-step video tutorials by Microsoft MVPs and experts. SALE $99.99 this month only -- learn more at: http://p.sf.net/sfu/learnmore_122912 _______________________________________________ Darktable-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/darktable-users
