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Lensrentals | all galleries >> photogeek_contest >> distortion_correction > coolthingcorrect.jpg
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Lensrentals15-Nov-2013 14:13
First I focused the lens (a Tokina 11-16mm) on infinity and set the zoom to 11mm. Afterwards I taped both focusing and zooming ring so that they do not turn anymore. Then, I took the image of our calibration room (no longer in use). Right afterwards, I used red-retro reflective targets from the iWitness package to setup a calibration field and took about 20 photos from this calibration field (you can see some of the retro targets in the image, which I added simply to put some colour into the image). With the calibration images, I used iWitness to calculate the radial symmetric, radial asymmetric and tangential distortion, as well as the shear and affinity of the sensor, principal point coordinates and corrected focal length.

I then loaded the raw image with RawTherapee and removed the chromatic aberration, as well as defringed it and cleaned it of impulse noise. Afterwards I saved the image as TIF file. Then I used a software that I wrote myself to undistort the image, using the parameters I've obtained from iWitness (I actually did not correct the principal point, as the image moved considerably to the left and didn't look so nice). I then saved it as a JPG and that's what you see in the corrected image.
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