I have an issue with trying to use the TCA parms to correct CA:
* I have a program that corrects distortion and CA using the EXIF info, the
Lensfun DB info and the magick program. The (barrel) distortion correction part
works quite well but I'm still trying to figure out the CA part.
* Using Magick, I split the image into red, green and blue channels. I use
the TCA Vr and Vb parms (* 100 to make them percentage values) to resize the
red and blue channels. I then re-combine the unchanged green channel image with
the resized red and blue channel images.
* I have been using some images taken with my Fuji X zooms (XC 16-50 and XC
50-230 and XF18-55) to test this. In most cases there isn't a lot of CA so this
has been a limitation. In those cases, when I apply the values from the DB,
there is no significant difference before and after (maybe because the
correction is minor?).
* I have one case from the XF 18-55 where there is some obvious blue/purple
fringing. When I apply the values from the DB it doesn't correct it. I
experimented with other values and found parameters that mostly eliminate the
fringing.
VR DB value: 1.0001664 My experimental value: 1.0007665
VB DB value: 0.9993813 My experimental value: 1.0004306
Obviously, there is quite a significant difference between the values that I
came up with compared with the ones in the DB. It makes me wonder if there is
something wrong with my methodology or if the values in the DB (in this case)
might be incorrect. I'd like the program to work for any lens in the DB so I
need to understand why this test case isn't working. Any feedback would be
appreciated.
I also haven't figured out where to find the latest version of the DB so an
answer to that would also be appreciated.
Chris
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