Hi All,
I've been working on a calibration for my new Canon G7 X following the method
here:
http://wilson.bronger.org/lens_calibration_tutorial/
For the vignette correction, I used a high-quality optical milk-glass diffuser to take the shots.
I've managed to get decent results for the distortion and tca, but the vignetting is not coming out
how I expected; it seems to be over-correcting (xml attached).
I'm trying to validate the resulting calibration by doing this:
* Open the same RAW files as were used to create the vignette calibration in
darktable
* Apply lens correction
* Use the color picker to check the brightness of pixels in the corners vs
those in the centre
For one example image from the set, before correction, (R,G,B):
centre: (218, 210, 204)
corner: (199, 196, 189)
after correction (only vignetting):
centre: (218, 210, 204)
corner: (255,255,255)
after correction (all corrections):
centre: (218, 210, 204)
corner: (240, 238, 234)
I then compared those values to the out-of-camera JPG (to compare to the in-camera correction) using
GIMP:
centre: (227, 220, 212)
corner: (215, 212, 205)
Is it just me or is lensfun/darktable over-correcting the vignette? Any
suggestions on how to fix this?
Thanks,
Rob
<lensdatabase>
<lens>
<maker>Canon</maker>
<model>Standard</model>
<mount>canonG7X</mount>
<cropfactor>2.709</cropfactor>
<calibration>
<distortion model="ptlens" focal="8.8" a="0.03542" b="-0.15684" c="0.05272" />
<distortion model="ptlens" focal="12.363" a="0.01144" b="-0.06208" c="0.01844" />
<distortion model="ptlens" focal="16.792" a="0.00282" b="-0.02201" c="0.00799" />
<distortion model="ptlens" focal="23.713" a="-0.00014" b="-0.0029" c="0.00441" />
<distortion model="ptlens" focal="36.8" a="-0.00282" b="0.0124" c="0.00016" />
<tca model="poly3" focal="8.8" br="-0.0002130" vr="1.0007586" bb="0.0003656" vb="0.9997358" />
<tca model="poly3" focal="8.8" br="-0.0005536" vr="1.0015980" bb="0.0004300" vb="0.9995689" />
<tca model="poly3" focal="8.8" br="-0.0005791" vr="1.0021067" bb="0.0006739" vb="0.9990885" />
<tca model="poly3" focal="8.8" br="-0.0006306" vr="1.0021097" bb="0.0006030" vb="0.9992007" />
<tca model="poly3" focal="8.8" br="-0.0006398" vr="1.0019492" bb="0.0005246" vb="0.9993929" />
<tca model="poly3" focal="8.8" br="-0.0006511" vr="1.0021924" bb="0.0006527" vb="0.9991038" />
<tca model="poly3" focal="8.8" br="-0.0006676" vr="1.0021085" bb="0.0006060" vb="0.9992401" />
<tca model="poly3" focal="11.5" br="-0.0002534" vr="1.0011377" bb="0.0001365" vb="0.9998125" />
<tca model="poly3" focal="11.5" br="-0.0002770" vr="1.0015103" bb="0.0003723" vb="0.9994313" />
<tca model="poly3" focal="11.5" br="-0.0002961" vr="1.0009145" bb="0.0001871" vb="0.9998068" />
<tca model="poly3" focal="11.5" br="-0.0003062" vr="1.0014792" bb="0.0003312" vb="0.9995216" />
<tca model="poly3" focal="11.5" br="-0.0003100" vr="1.0015846" bb="0.0003888" vb="0.9994046" />
<tca model="poly3" focal="11.5" br="-0.0003287" vr="1.0014255" bb="0.0002251" vb="0.9996835" />
<tca model="poly3" focal="14.2" br="-0.0001426" vr="1.0008935" bb="0.0000263" vb="0.9999808" />
<tca model="poly3" focal="14.2" br="-0.0001585" vr="1.0007047" bb="0.0000206" vb="0.9999799" />
<tca model="poly3" focal="14.2" br="-0.0001697" vr="1.0010616" bb="0.0001573" vb="0.9997751" />
<tca model="poly3" focal="14.2" br="-0.0001722" vr="1.0010225" bb="0.0000968" vb="0.9998675" />
<tca model="poly3" focal="14.2" br="-0.0001761" vr="1.0011549" bb="0.0002442" vb="0.9996616" />
<tca model="poly3" focal="14.2" br="-0.0001772" vr="1.0011291" bb="0.0002394" vb="0.9996655" />
<tca model="poly3" focal="18.4" br="-0.0001133" vr="1.0003816" bb="-0.0000293" vb="1.0000873" />
<tca model="poly3" focal="18.4" br="-0.0001207" vr="1.0005166" bb="-0.0000036" vb="1.0000975" />
<tca model="poly3" focal="18.4" br="-0.0001217" vr="1.0005797" bb="0.0000737" vb="0.9999569" />
<tca model="poly3" focal="18.4" br="-0.0001400" vr="1.0006308" bb="0.0000998" vb="0.9999035" />
<tca model="poly3" focal="18.4" br="-0.0001473" vr="1.0006839" bb="0.0001503" vb="0.9998396" />
<tca model="poly3" focal="18.4" br="-0.0001493" vr="1.0006885" bb="0.0001509" vb="0.9998417" />
<tca model="poly3" focal="25.2" br="-0.0000682" vr="1.0001115" bb="0.0000440" vb="0.9999814" />
<tca model="poly3" focal="25.2" br="-0.0000702" vr="1.0000477" bb="0.0000084" vb="0.9999847" />
<tca model="poly3" focal="25.2" br="-0.0000722" vr="1.0001732" bb="0.0000798" vb="0.9998783" />
<tca model="poly3" focal="25.2" br="-0.0000781" vr="1.0001607" bb="0.0000489" vb="0.9999710" />
<tca model="poly3" focal="25.2" br="-0.0000797" vr="1.0001892" bb="0.0000805" vb="0.9998795" />
<tca model="poly3" focal="25.2" br="-0.0000853" vr="1.0001835" bb="0.0000673" vb="0.9999078" />
<tca model="poly3" focal="36.8" br="-0.0000801" vr="0.9998473" bb="0.0000400" vb="0.9998099" />
<tca model="poly3" focal="36.8" br="-0.0000906" vr="0.9998536" bb="0.0000231" vb="0.9998562" />
<tca model="poly3" focal="36.8" br="-0.0000980" vr="0.9998622" bb="0.0000372" vb="0.9998263" />
<tca model="poly3" focal="36.8" br="-0.0000983" vr="0.9999278" bb="0.0000610" vb="0.9997855" />
<tca model="poly3" focal="36.8" br="-0.0001157" vr="0.9998624" bb="0.0000597" vb="0.9997425" />
<vignetting model="pa" focal="8.8" aperture="1.8" distance="10" k1="-0.0105" k2="-0.7799" k3="0.0346" />
<vignetting model="pa" focal="8.8" aperture="1.8" distance="1000" k1="-0.0105" k2="-0.7799" k3="0.0346" />
<vignetting model="pa" focal="8.8" aperture="2.5" distance="10" k1="0.1882" k2="-0.9886" k3="0.0520" />
<vignetting model="pa" focal="8.8" aperture="2.5" distance="1000" k1="0.1882" k2="-0.9886" k3="0.0520" />
<vignetting model="pa" focal="8.8" aperture="3.5" distance="10" k1="0.1626" k2="-0.7989" k3="-0.1299" />
<vignetting model="pa" focal="8.8" aperture="3.5" distance="1000" k1="0.1626" k2="-0.7989" k3="-0.1299" />
<vignetting model="pa" focal="8.8" aperture="5" distance="10" k1="0.0470" k2="-0.2487" k3="-0.5696" />
<vignetting model="pa" focal="8.8" aperture="5" distance="1000" k1="0.0470" k2="-0.2487" k3="-0.5696" />
<vignetting model="pa" focal="8.8" aperture="11" distance="10" k1="-0.0492" k2="0.1611" k3="-0.6432" />
<vignetting model="pa" focal="8.8" aperture="11" distance="1000" k1="-0.0492" k2="0.1611" k3="-0.6432" />
<vignetting model="pa" focal="12.2" aperture="2.2" distance="10" k1="-0.6699" k2="1.2404" k3="-1.1205" />
<vignetting model="pa" focal="12.2" aperture="2.2" distance="1000" k1="-0.6699" k2="1.2404" k3="-1.1205" />
<vignetting model="pa" focal="12.2" aperture="3.2" distance="10" k1="-0.1206" k2="0.3246" k3="-0.7036" />
<vignetting model="pa" focal="12.2" aperture="3.2" distance="1000" k1="-0.1206" k2="0.3246" k3="-0.7036" />
<vignetting model="pa" focal="12.2" aperture="4.5" distance="10" k1="-0.3018" k2="0.8563" k3="-1.0518" />
<vignetting model="pa" focal="12.2" aperture="4.5" distance="1000" k1="-0.3018" k2="0.8563" k3="-1.0518" />
<vignetting model="pa" focal="12.2" aperture="6.3" distance="10" k1="-0.3459" k2="0.9753" k3="-1.0974" />
<vignetting model="pa" focal="12.2" aperture="6.3" distance="1000" k1="-0.3459" k2="0.9753" k3="-1.0974" />
<vignetting model="pa" focal="12.2" aperture="9" distance="10" k1="-0.2780" k2="0.7635" k3="-0.8598" />
<vignetting model="pa" focal="12.2" aperture="9" distance="1000" k1="-0.2780" k2="0.7635" k3="-0.8598" />
<vignetting model="pa" focal="12.2" aperture="11" distance="10" k1="-0.2242" k2="0.6111" k3="-0.6876" />
<vignetting model="pa" focal="12.2" aperture="11" distance="1000" k1="-0.2242" k2="0.6111" k3="-0.6876" />
<vignetting model="pa" focal="16.8" aperture="2.5" distance="10" k1="-0.5000" k2="0.9117" k3="-0.8914" />
<vignetting model="pa" focal="16.8" aperture="2.5" distance="1000" k1="-0.5000" k2="0.9117" k3="-0.8914" />
<vignetting model="pa" focal="16.8" aperture="3.5" distance="10" k1="-0.1701" k2="0.4883" k3="-0.7899" />
<vignetting model="pa" focal="16.8" aperture="3.5" distance="1000" k1="-0.1701" k2="0.4883" k3="-0.7899" />
<vignetting model="pa" focal="16.8" aperture="5" distance="10" k1="-0.3171" k2="1.0160" k3="-1.1433" />
<vignetting model="pa" focal="16.8" aperture="5" distance="1000" k1="-0.3171" k2="1.0160" k3="-1.1433" />
<vignetting model="pa" focal="16.8" aperture="7.1" distance="10" k1="-0.3214" k2="1.0095" k3="-1.1005" />
<vignetting model="pa" focal="16.8" aperture="7.1" distance="1000" k1="-0.3214" k2="1.0095" k3="-1.1005" />
<vignetting model="pa" focal="16.8" aperture="10" distance="10" k1="-0.2466" k2="0.7703" k3="-0.8386" />
<vignetting model="pa" focal="16.8" aperture="10" distance="1000" k1="-0.2466" k2="0.7703" k3="-0.8386" />
<vignetting model="pa" focal="16.8" aperture="11" distance="10" k1="-0.2213" k2="0.6874" k3="-0.7447" />
<vignetting model="pa" focal="16.8" aperture="11" distance="1000" k1="-0.2213" k2="0.6874" k3="-0.7447" />
<vignetting model="pa" focal="23.4" aperture="2.8" distance="10" k1="-0.3033" k2="1.1103" k3="-1.2516" />
<vignetting model="pa" focal="23.4" aperture="2.8" distance="1000" k1="-0.3033" k2="1.1103" k3="-1.2516" />
<vignetting model="pa" focal="23.4" aperture="4" distance="10" k1="-0.2629" k2="0.9027" k3="-1.0664" />
<vignetting model="pa" focal="23.4" aperture="4" distance="1000" k1="-0.2629" k2="0.9027" k3="-1.0664" />
<vignetting model="pa" focal="23.4" aperture="5.6" distance="10" k1="-0.3082" k2="1.0427" k3="-1.1347" />
<vignetting model="pa" focal="23.4" aperture="5.6" distance="1000" k1="-0.3082" k2="1.0427" k3="-1.1347" />
<vignetting model="pa" focal="23.4" aperture="8" distance="10" k1="-0.2870" k2="0.9676" k3="-1.0464" />
<vignetting model="pa" focal="23.4" aperture="8" distance="1000" k1="-0.2870" k2="0.9676" k3="-1.0464" />
<vignetting model="pa" focal="23.4" aperture="11" distance="10" k1="-0.2156" k2="0.7239" k3="-0.7793" />
<vignetting model="pa" focal="23.4" aperture="11" distance="1000" k1="-0.2156" k2="0.7239" k3="-0.7793" />
<vignetting model="pa" focal="36.8" aperture="2.8" distance="10" k1="-0.2338" k2="0.3663" k3="-0.6196" />
<vignetting model="pa" focal="36.8" aperture="2.8" distance="1000" k1="-0.2338" k2="0.3663" k3="-0.6196" />
<vignetting model="pa" focal="36.8" aperture="4" distance="10" k1="-0.2422" k2="0.8624" k3="-1.0557" />
<vignetting model="pa" focal="36.8" aperture="4" distance="1000" k1="-0.2422" k2="0.8624" k3="-1.0557" />
<vignetting model="pa" focal="36.8" aperture="5.6" distance="10" k1="-0.3299" k2="0.9762" k3="-1.0638" />
<vignetting model="pa" focal="36.8" aperture="5.6" distance="1000" k1="-0.3299" k2="0.9762" k3="-1.0638" />
<vignetting model="pa" focal="36.8" aperture="8" distance="10" k1="-0.2979" k2="0.8664" k3="-0.9437" />
<vignetting model="pa" focal="36.8" aperture="8" distance="1000" k1="-0.2979" k2="0.8664" k3="-0.9437" />
<vignetting model="pa" focal="36.8" aperture="11" distance="10" k1="-0.2300" k2="0.6667" k3="-0.7238" />
<vignetting model="pa" focal="36.8" aperture="11" distance="1000" k1="-0.2300" k2="0.6667" k3="-0.7238" />
</calibration>
</lens>
</lensdatabase>
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