Hi,
since I wasn't satiesfied with the result of lensfun's distortation
correction (at short focus lengthes),
I approached it the problem a different way. To sum up the results are
optimal - in a certain sense, see below.
This is what I did:
- prepare a sheet of paper with some labeled grid with thin lines
- take photographs of this at different focal lengthes
- IMPORT : adjust the FZ1000 to store both, the JPEG and the raw file
(.RW2)
- ufraw-batch --lensfun=none --out-depth=8 --out-type=jpeg
--output=Test.RW2.jpeg Test.RW2
- open both, Test.JPG (from the camera) and Test.RW2.jpeg in Gimp
- note several coordinates of unique points in both images
- compute the radii of all points and scale them to half of the height
of an image ( = 1.0/1824 for the FZ1000)
- using Octave I fitted a polynomial of the form
r*(d+r*(c+r*(b+r*a))) to the data using a smoothed maximum norm
- check this polynomial by using convert (ImageMagick) e.g.
a b c d
convert Test.RW2.jpeg -define distort:viewport=5472x3648+8+8
-distort Barrel 0.026153,-0.102825,0.021310,0.997913 New.jpeg
- open both, Test.JPG and New.jpeg as layers in Gimp, desatured both
and switch to difference layer mode
Result: this images are identical (except the intensities of gray
tones). This means, that the polynom computed by me produces excatly
the same
lens correction as the camera (FZ1000) does it itself.
Unfortunately the coefficient d differs from 1 which is an assumption
in lensfun.
Is there a way to use or patch lensfun to use all 4 parameters (e.g. a
general d)?
Here are my results:
The focal lengthes here are scaled by the crop factor
focal length d c b a
25 0.997913 0.0213096 -0.102825 0.0261528
28 1.00083 0.019843 -0.0899886 0.0237594
35 0.998356 0.0194224 -0.0581771 0.0137862
50 1.00373 -0.00242727 -0.0103302 0.00130064
70 1.0011 0.00645453 -0.0102541 0.00258168
90 1.00838 -0.0245663 0.0221847 -0.00623619
Thanks for your comments,
Helmut
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