Wish I had looked here first.
A couple of the questions I asked at povray.binaries.images seem answered 
here. I was wondering if the bandwidth was adjustable, guess thats 
'dispersion'; and whether the contrast were changeable, but I guess not since 
both test images were of equal contrast and the only other keyword, 
'disp_nelems', is the smoothness of color not lightness/darkness.
Well, I'm not about to look a gift-horse in the mouth.
Great to see the spectral dispersion make it to 3.1 in source form.
Still would like to hear what render time is like with it as I'm sure many 
would.

Bob

Message <3660C507.EE074F44@pipeline.com>, Daren Scot Wilson  typed...
>
>This is a multi-part message in MIME format.
>--------------036A88D3F4349E816EB2C8BB
>Content-Type: text/plain; charset=us-ascii
>Content-Transfer-Encoding: 7bit
>
>The attached file is a tarred gzipped file containing a patch and a
>readme.  The patch adds color dispersion to POV-Ray 3.10 (and I assume
>3.10a, but I haven't tried it yet).
>
>There are two new keywords:  dispersion and disp_nelems.  Use them like
>this:
>
>sphere { <...someplace...>, R
>        pigment { color rgbf <1,1,1,1> }
>        finish {
>                ambient 0
>                phong .3
>                phong_size 120
>        }
>        interior {
>                ior  1.3
>                dispersion 1.05
>                disp_nelems 15
>        }
>}
>
>
>The dispersion value is the ratio of IOR values for violet to red.  Good
>numbers are 1.01 to 1.1.    The IOR value given by the ior keyword is
>taken to be for yellow-green, the color at the center of the spectrum.
>
>The disp_nelems is optional, but the default value I gave it is only 7,
>too small if the dispersion value is large, like > 1.1 or so.  
>
>Because the dispersion modification was built on a version of source
>code I had already added some features to, you get some other features: 
>keywords #endif and #endwhile, to be paired with #if and #while
>statements (only for the Human's convenience), and new degree-trig
>functions  sind, cosd, tand, asind, acosd, atan2d  which take or return
>degrees instead of radians.  Someday, I will separate the dispersion and
>degrees-trig features as separate patches.  Someday....
>
>Everything on my web site about dispersion that you've read before Nov.
>29 1998 is obsolete. That was a clumsy brute-force algorithm that
>affected many source code files. This patch is a new algorithm that
>affects only one subroutine in one file, plus simple changes to add new
>keywords to the parser.  It should be easy to combine with other
>patches.
>
>An example image will be posted to povray.binaries.images and
>povray.binaries.scene-files.  All this stuff will appear on my web page
>at http://www.newcolor.com/darenw/dswpov/disp.html.  (In a couple of
>days)
>
>Be careful, as this is the *first* release to the world of this patch. 
>It works on my machine, but if it doesn't on yours, send me e-mail and
>we'll fix it.  Stay tuned for corrections, updates, etc...
>
>-- 
>
>Daren Scot Wilson
>Member, ACM
>dar### [at] pipelinecom
>www.newcolor.com
>--

-- 
 omniVERSE: beyond the universe
  http://members.aol.com/inversez/POVring.html
=Bob

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