## Re: [PanoToolsNG] Re: Reverse distortion correction

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• Hi Tim, ... I see, the values are in mm relative to h from centre to top right corner of portrait orientation and expressed in percentage. ... rsrc is the
Message 1 of 7 , Oct 19, 2007
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Hi Tim,
> What I have is data sets which produce something like the graph Figure
> 3 (A) on http://www.vanwalree.com/optics/distortion.html
I see, the values are in mm relative to h from centre to top right corner
of portrait orientation and expressed in percentage.

> Looking at the Lens Correction Model details on
> http://wiki.panotools.org/Lens_correction_model it seems I want to
> convert my data to actual radial distances so rsrc and rdest are
> specified (is src or dest the 'corrected' distance?) rather than a
> percentage.

rsrc is the source image and rdest is the destination, the corrected image.
The radial distance r_src for each point in the source image is computed
by the formula:
r_src = (a * r_dest^3 + b * r_dest^2 + c * r_dest + d) *
r_dest
Units for r_src and r_dest is image width / 2, ie the edge of the image
corresponds to r_src = 1.
The internal unit used for r_src and r_dest _ is the smaller of the two
image lengths divided by 2.

> I presume I can then take my data and if say rsrc is 35 and rdest 38,
> I can swap the source and destination and refit the polynomial - will
> this give the the parameters needed to introduce distortion?
You would need to convert your percentages of h in mm to positive or
negativ pixel distance values of a,b and c and apply the PTcorrect tool
with its reverted values.

I did a short test of a lens correction and reverted a corrected duplicate
with the PTcorrect tool with reverted values (positive to negativ and vice
versa.) overlayed as layers in PS to show the difference. It is perfect,
but cropped by dimensions lost in the original lens correction. PtGui will
do the same with more canvas to play with.

Here is the link to the paper from Prof. Dersch to explain its functions:
http://www.all-in-one.ee/~dersch/barrel/barrel.html

Cheers, Milko

--
Milko K. Amorth
360° Immersive Imaging Productions

Vancouver.360cities.net
Ph:604.561.5101
fx: 604.909.5125

Skype: VRdundee