Hallöchen! Helmut Jarausch writes:
> On 06/16/2016 05:31:05 PM, Torsten Bronger wrote: > >> Helmut Jarausch writes: >> >>> On 06/16/2016 01:52:38 PM, Torsten Bronger wrote: >>> >>> [...] >>> >>>> [...] But can't you just use the Lensfun formula in Octave? >>> >>> Of course, I could, but it won't make sense. As one can see in >>> the table below, the sum of the coefficients is (significantly) >>> smaller than 1. >> >> But if you replace d with 1-a-b-c, and you should get different >> values for a, b, and c, namely those for which a+b+c+d = 1. > > Yes, but I don't want this. [...] Okay, fair enough, but it would work and does not affect accuracy. >>> If one compares a raw image which has been processed without lens >>> correction with the JPEG file coming from the camera, one observes >>> that the camera enlarges and then crops the image, i.e. it's >>> clearly visible that the JPEG file has a (slightly) smaller range >>> of view. Probably, Panasonic does so to cut off uncorrectable >>> distortions at the boundary of the raw image. >> >> As does Lensfun, at least in the ptlens and poly3 models >> (unfortunately; I'd love to change that). d is the scaling factor. >> In a sensible model, d = 1. > > I doubt that. The image is scaled by Lensfun by 1-a-b-c=d. But maybe we mean different things with "scaling"? I mean that the *centre* of the image is scaled, where the anti-distortion should have no effect. In other words, for r -> 0, the change in r should vanish. In Lensfun, however, (with ptlens and poly3) the change in r in the centre is d. I admit that black parts in the corners remain in case of pincushion distortion. > Before I started my own investigations I was disappointed by the > results of Darktable which uses Lensfun. This may happen with a bad calibration. But whether you use a',b',c',d' or a,b,c has no effect on accuracy. In fact, both can be transformed into another: a = a' / d'^4 b = b' / d'^3 c = c' / d'^2 (I hope I got the / or * right.) 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
