Path: utzoo!utgpu!watmath!clyde!att!osu-cis!tut.cis.ohio-state.edu!bloom-beacon!apple!oliveb!sun!arabian!jamesa
From: jamesa@arabian.Sun.COM (James D. Allen)
Newsgroups: comp.graphics
Subject: Re: Pixar's noise function
Keywords: random numbers, Byte, elephants
Message-ID: <97699@sun.Eng.Sun.COM>
Date: 5 Apr 89 23:02:44 GMT
References: <2553@ssc-vax.UUCP> <3599@pixar.UUCP>
Sender: news@sun.Eng.Sun.COM
Lines: 27

In article <3599@pixar.UUCP>, aaa@pixar.UUCP (Tony Apodaca) writes:
> In article <2553@ssc-vax.UUCP> coy@ssc-vax.UUCP (Stephen B Coy) writes:
> >	Last night I saw the article in Byte about the Renderman
> >standard.  In the sample source code the displacement function, dent(),
> >calls a function called noise()...
> >          ...My question:  Does anyone out there know what this
> >noise function really is?
> 
> ... Conceptually, noise()
> is a "stochastic three-dimensional function which is statistically
> invariant under rotation and translation and has a narrow bandpass
> limit in frequency" (paraphrased from [Perlin1985]).  This means that
> you put three-space points in, and you get values back which are basically
> random.  But if you put other nearby points in, you get values that are
> very similar.  The differences are still random, but the maximum rate of
> change is controlled so that you can avoid aliasing.  If you put a set
> of points in from a different region of space, you will get values out
> which have "the same amount" of randomness.

	Anyone willing to post a detailed description of such an
	algorithm?  (Jon Buller posted one, but I couldn't figure it out:
	what is `Pts'?)
> -- 
> UUCP:		{sun,ucbvax}!pixar!aaa		Tony Apodaca
> ARPA,BITNET:	aaa%pixar.uucp@sun.com		Pixar, San Rafael, CA, USA

-James Allen