My First Spectral rendering

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jbikker
Posts: 175
Joined: Mon Nov 28, 2011 8:18 am
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My First Spectral rendering

Postby jbikker » Fri Jun 09, 2017 10:19 am

Been playing with spectral rendering:

spectraldragon.jpg
spectraldragon.jpg (156.18 KiB) Viewed 1267 times


Completely new world for me so be gentle. :)
This is with tracing four wavelengths at once; three of them are killed when a wavelength dependent pure specular dielectric is encountered.

The tracer accumulates CIE XYZ colors and converts them to RGB using the approach proposed by Brian Smits (http://www.cs.utah.edu/~bes/papers/color/paper.pdf). I chose not to use the more accurate method of Meng et al., (https://jo.dreggn.org/home/2015_spectrum.pdf) as it requires substantially more involved calculations.

EDIT: another one:

dragon_spectral.jpg
dragon_spectral.jpg (105.32 KiB) Viewed 1246 times


This is unidirectional path tracing so the caustics took a while to converge, and they are still noisy...

shocker_0x15
Posts: 61
Joined: Sun Aug 19, 2012 3:24 pm

Re: My First Spectral rendering

Postby shocker_0x15 » Thu Jun 15, 2017 5:46 am

Cool ;)

What is the material?
Do you implement Hero wavelength spectral sampling?

jbikker
Posts: 175
Joined: Mon Nov 28, 2011 8:18 am
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Re: My First Spectral rendering

Postby jbikker » Thu Jun 15, 2017 7:21 am

Quartz. I'm tracing four wavelengths as proposed by the Hero paper, but I have not implemented their MIS scheme yet. In this case it's useless by the way; the quartz will reduce weights for all wavelengths but the hero to zero anyway. For the floor and walls the four wavelengths are very effective, obviously.

ziu
Posts: 28
Joined: Sat Aug 17, 2013 8:46 pm

Re: My First Spectral rendering

Postby ziu » Thu Jun 15, 2017 11:38 am

Since we're talking secondaries here, did you guys notice this article?
"Building an Orthonormal Basis, Revisited"; Tom Duff, James Burgess, Per Christensen, Christophe Hery, Andrew Kensler,
Max Liani, and Ryusuke Villemin:
http://jcgt.org/published/0006/01/01/paper.pdf

It describes a fast and accurate way to generate an orthonormal basis for things like random sampling. I got the link from a Twitter post by Carmack some time ago but I don't remember seeing it linked here yet.

I watched the Hero presentation at EGSR a couple years back. The results looked really excellent.

jbikker
Posts: 175
Joined: Mon Nov 28, 2011 8:18 am
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Re: My First Spectral rendering

Postby jbikker » Thu Jun 15, 2017 12:26 pm

I hadn't seen it, but it looks good.
On a related note: https://www.shadertoy.com/view/lssfD7 , Lambert reflection without tangents.

friedlinguini
Posts: 79
Joined: Thu Apr 11, 2013 5:15 pm

Re: My First Spectral rendering

Postby friedlinguini » Thu Jun 15, 2017 1:59 pm

Whoah, weird. I had thought you could do something very similar, but by adding a random point on the *interior* of a sphere to the normal, rather than on the surface: http://psgraphics.blogspot.com/2014/09/ ... -rays.html. Obviously it would be better to use exactly two random parameters than an unbounded number of them, but I have a hard time wrapping my brain around the possibility that both are correct.


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