[Bf-committers] Movie distortion algorithm
j.bakker at atmind.nl
j.bakker at atmind.nl
Tue Apr 17 12:05:50 CEST 2012
Hi,
Thanks for the feedback Jonathan & Michael. You are probably right.
Currently we already have a look-up grid that is precalculated. It is a
nice-to-have feature to speed-up this precalculation process. Current
lookup grid is per pixel. In a 4k shot it just takes a very long time.
Perhaps it is an idea that these grids are eventually stored to disk.
Regards,
Jeroen Bakker.
Original Message:
-----------------
From: mgschwan at blensor.org
Date: Tue, 17 Apr 2012 11:06:17 +0200
To: bf-committers at blender.org
Subject: Re: [Bf-committers] Movie distortion algorithm
I second that,
using a precomputed mapping will be the most useful algorithm. Because
normally, everybody is doing the reverse mapping (undistortion by
calculating the distorted positions from the undistorted ones and doing
a reverse mapping) and avoids the other way around like the devil runs
from the holy water.
What could be a feasible solution too:
Calculate the distorted points from the undistorted ones and
interpolate between the supporting points with a 2nd order polynomial.
Maybe you even could reduce the number of supporting points by
calculating only a sparse mapping between undistorted and distorted
points. Basically doing a piecewise polynomial interpolation.
Michael
Am 17.04.2012 00:43, schrieb Jonathan Merritt:
> Reading that paper (Vass and Perlaki), they present a very good
> solution.
> If you're running the inverse transformation on a sequence of
> frames, all
> of which have the same distortion parameters, then just compute the
> inverse
> transformation once ("slow"), and cache the result. Then do a
> look-up
> using either exact values or some kind of fast interpolation for all
> of
> your movie frames.
>
> They also describe using Newton's method to compute the (xd, yd) =>
> (x,y)
> transformation, as I suggested. Since these guys have already looked
> at
> this problem, I suspect that the algebraic inverse transformation is
> probably very long and painful.
>
> Even if your distortion parameters are varying, you could also speed
> up the
> process by using the solution from the previous frame as the staring
> point
> for your Newton iteration of the next frame.
>
> On Mon, Apr 16, 2012 at 4:06 PM, Dan Eicher <dan at trollwerks.org>
> wrote:
>>
>>> These guys describe a fast preview mode (if that's the problem):
>>>
>>> http://www.vassg.hu/pdf/vass_gg_2003_lo.pdf
>>>
>>> ...not that I understand the math behind it.
>>>
>>> Dan
>>> _______________________________________________
>>> Bf-committers mailing list
>>> Bf-committers at blender.org
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>>>
>>
>>
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