Dear all, >> I thought that I understood how it works, and that the ImageMagick command >> below will do the same correction as the lens profile below. >> <vignetting model="pa" focal="250" aperture="4" distance="1000" >> k1="0.0" k2="-0.156" k3="-0.711" /> >> convert IMGP4694.tiff -fx "Xi=i-w/2; Yj=j-h/2; >> r=hypot(Xi,Yj)/hypot(w/2,h/2); s/(1-0.156*r^4-0.711*r^6)" >> IMGP4694-corrected.tiff >> >> But it is not the case. > > I don't know why this does not work. It looks correct. However, > the coefficients are unrealistic in my opinion. FWIW, I've never > seen a lens with a such sudden fall-off, not even fish-eyes.
You can download a DNG sample at http://dl.free.fr/grImV4Y5M The coefficients above work well on this picture (using darktable) but not on the TIFF. In my first experiments I created the TIFF using ufraw --create-id=also --out-type=tiff --out-depth=16 IMGP4694.DNG (with no lens profile). An explanation could be that this conversion from DNG to TIFF is no coherent with the way darktable works, and therefore I made the conversion by having darktable create a 16-bit TIFF; it gives other TIFF, but correcting the vignetting with ImageMagick and the same parameters is not working either. >> PS: There is another addition to lensfun that would be useful for >> the owners of Pentax bodies: taking into account the position of >> the optical center. Because the sensor may not be centered (due to >> shake reduction, or composition adjustment) and therefore the >> vignetting intensity is not the same in every corner. > > Lensfun has the <center> tag, see > <http://lensfun.sourceforge.net/manual/el_lens.html>. But I don't > accept it in the database unless I'm convinced that a certain lens > model has the same de-centering with each lens sample. What I was describing is not a lens centring issue, it is a consequence of the sensor displacement. The center of the lens does not coincide with the center of the sensor, and there is in the EXIF the information about the sensor displacement. Therefore it can be used in a generic manner, unlike lens de-centering with depends on the sample (and cannot be corrected by software when it causes some loss of resolution on one side). Regards, Louis ------------------------------------------------------------------------------ Check out the vibrant tech community on one of the world's most engaging tech sites, SlashDot.org! http://sdm.link/slashdot _______________________________________________ Lensfun-users mailing list Lensfun-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/lensfun-users
