POV-Ray : Newsgroups : povray.binaries.images : Reduction of noise generator grid artifact Server Time
17 Nov 2024 02:22:07 EST (-0500)
  Reduction of noise generator grid artifact (Message 1 to 4 of 4)  
From: Slime
Subject: Reduction of noise generator grid artifact
Date: 14 Oct 2002 15:33:22
Message: <3dab1c02$1@news.povray.org>
Thanks to a discussion in povray.advanced-users, someone mentioned an SCurve
function that matches up the second derivatives much better. I've
implemented this as a noise_generator option (activated by the keyword
"match_second_derivatives"). The result is certainly an improvement. The
grid *is* still visible, partially because the noise function is based on a
grid of values, and partially because the 3rd, etc derivatives still don't
match up.

The attached version shows each noise generator (4 is my 4D noise generator
with slice set to 0.5) used as a normal pattern on a sphere. Note that these
have the fix_shadow_line flag on (described in an earlier post to this
group, see "My recent work").

The fixed version rendered slower, of course, but it will be useful in the
occasional instance where unturbulated noise is used for isosurface
displacement or for normals.

 - Slime
[ http://www.slimeland.com/ ]


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Attachments:
Download 'noisefuncgridfix.jpg' (40 KB)

Preview of image 'noisefuncgridfix.jpg'
noisefuncgridfix.jpg


 

From: Hugo
Subject: Re: Reduction of noise generator grid artifact
Date: 14 Oct 2002 17:15:28
Message: <3dab33f0@news.povray.org>
Very nice to see all your work related to fixing / expanding the POV code.
Your efforts are appreciated.

Regards,
Hugo


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From: Ben Birdsey
Subject: Re: Reduction of noise generator grid artifact
Date: 14 Oct 2002 18:38:54
Message: <3DAB4717.3C7597D5@mail.com>
Slime -

Good work.  Another way to eliminate the banding would be to use the
Catmull-Rom form of of a cubic (or higher order) spline.  However, I'm
pretty sure that this would significantly increase the evaluation time
:(

- Ben


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From: Christopher James Huff
Subject: Re: Reduction of noise generator grid artifact
Date: 18 Oct 2002 10:47:07
Message: <chrishuff-478D38.10421018102002@netplex.aussie.org>
In article <3dab1c02$1@news.povray.org>, "Slime" <slm### [at] slimelandcom> 
wrote:

> The fixed version rendered slower, of course, but it will be useful in the
> occasional instance where unturbulated noise is used for isosurface
> displacement or for normals.

While the new interpolation function is slower than the old one, Perlin 
made some other optimizations so the result is actually faster...you 
might want to look into those other changes.

-- 
Christopher James Huff <cja### [at] earthlinknet>
http://home.earthlink.net/~cjameshuff/
POV-Ray TAG: chr### [at] tagpovrayorg
http://tag.povray.org/


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