Hallöchen! Helmut Jarausch writes:
> [...] > > I've modified the lensfun data in my installation according to > your suggestion. [...] The two images are very different. Well, I could only use gnuplot, so it was kind of "blind flying" for me. Would you mind uploading the 25mm-close-focus image pair somewhere, e.g. at http://wilson.bronger.org/calibration? Thanks! > Even if there would be some additional transformation it would too much > work: > > darktable / export / Gimp rescaling + cropping / import into > darktable. Yes, this is not senseful. > [...] > > Perhaps I can find a way to patch Rawtherapee which doesn't use > lensfun. If you prefer DT over RT, patching Lensfun allows for a simpler workflow. Possibly the following – hopefully not too tedious – background info is helpful for you to understand the implications of that polynomial. Mathematically, if scaling doesn't matter to you, the a,b,c,d set becomes under-determined, and you can set any of the parameters to a non-degenerated value without losing accuracy, which I did in the post with the transformation method. An overview of different models gives <http://wilson.bronger.org/lensfun/group__Lens.html#gaa505e04666a189274ba66316697e308e>. As you can see, only the Hugin-inherited models have d not equal to 1. Both Imatest and Adobe (Lightroom) set d=1. Note that Adobe has five parameters, but no d nevertheless. On <http://www.panotools.org/dersch/barrel/barrel.html>, Helmut Dersch, creator of PanoTools and an active researcher in this field, discusses the polynomial and explains that "d" is the scaling parameter. I scales in the sense that it changes the scale in the centre of the image, i.e. in the <https://en.wikipedia.org/wiki/Paraxial_approximation> (where the focal length is defined). Of course, one cannot just change d and the image gets bigger or smaller, the other parameters must be changed, too, which is why I removed a misleading part from the PanoTools docs: http://wiki.panotools.org/index.php?title=Lens_correction_model&diff=14463&oldid=14358 By the way, for Lensfun, d != 1 is really unfortunate, because we need to preserve the effective focal length for certain algorithms. Thus, Lensfun jumps through some hoops for un-doing the scaling. Hope this clears up some things ... Tschö, Torsten. -- Torsten Bronger Jabber ID: [email protected] ------------------------------------------------------------------------------ What NetFlow Analyzer can do for you? Monitors network bandwidth and traffic patterns at an interface-level. Reveals which users, apps, and protocols are consuming the most bandwidth. Provides multi-vendor support for NetFlow, J-Flow, sFlow and other flows. Make informed decisions using capacity planning reports. http://sdm.link/zohomanageengine _______________________________________________ Lensfun-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/lensfun-users
