Hallöchen! Louis Granboulan writes:
> [...] > > My idea was to use the Fx special effects of ImageMagick to > experiment with various correction formulas. But I have not been > able to reproduce with ImageMagick the effect of using lensfun > profiles in darktable. > > [...] The page > http://lensfun.sourceforge.net/manual/group__Lens.html#ga3fd9e8dbe500297bdda2d6458745b481 > says that the correction is obtained by multiplying by M, [...] The Lensfun page is incorrect. I corrected it in the source code. > 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. > [...] > > I guess that instead of having a (parametric) formula to correct > brightness depending only on the distance to the center, the > correction profile could be a low-resolution image that lensfun > would scale up to the picture size and use to. This plus bilinear interpolation is the plan. > [...] > > 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. Tschö, Torsten. -- Torsten Bronger ------------------------------------------------------------------------------ Developer Access Program for Intel Xeon Phi Processors Access to Intel Xeon Phi processor-based developer platforms. With one year of Intel Parallel Studio XE. Training and support from Colfax. Order your platform today.http://sdm.link/xeonphi _______________________________________________ Lensfun-users mailing list Lensfun-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/lensfun-users
