My experiments with atmospheric effects


by
Marcos Fajardo

Motivation

This page is about some boring test images made with my experimental realistic rendering engine, which is still under development (and probably will be so for a few decades :-). Please, note that these are just TESTS which I made on the fly while coding the features you can see in them; geometry and textures are very simple, since I wasn't thinking in exposing the pictures to any eyes but mine. In order to get the most out of these JPEG images, watch them in a 24 bit display (seems obvious, but I think it's worth mentioning). Even in such displays, they are still low quality images, due to JPEG's type of compression. File sizes range from 30 to 70 kb.

Hey, if you are interested in any technical details about these images, or just want to chat about related topics (metaballs/blobs/soft objects, ray tracing, radiosity, relativistic effects, ... and clever ways to accelerate those ones), contact me!. I will be very happy hearing from you. Try locating me in IRC, where we can have nice chats, typing /whois MarcosF. Odds are that you'll find me on channels #raytracing, #3d, #lightwave, #coders or somesuch. It would be great to exchange papers with you. I'm specifically looking for lens flare and metaball stuff. I have japanese friends who can help me translating japanese text, so if you have access to the genuine metaball paper by K. Omura et al. [6], please let me know. Thanks in advance!

By the way, do you know about Eric Johnson, that amazing Texan fret whiz?... What? Ah via Musicom is your fave CD, too? ... Yeah, you are right, he is the best! ;-)



I've recently finished POVAFX 1.0, a hacked POV-Ray 2.2 with a couple of these effects.

Featuring

Coming soon...


Glowing lights

These simple images demonstrate how the atmosphere glows in the vecinity of a point light source. I'm trying different models of light absorption/scattering. As you can see clearly in the first picture, there are functions that make the intensity of scattered light sweep into infinity near the light source, resulting in highly saturated images; cool for special effects but not very physically correct... You can find this simple model in [1].

Ground fog

With and without ground fog. The particle density decreases exponentially along the Z axis. You can also have several layers of fog, each one with its own color, density and altitude (I'm still improving it, though). One interesting reference here is [2].

Cylindrical/conical spotlights

Also, my ray tracing kernel deals easily with cylindrical/conical spotlights within the fog, and it won't perform volume sampling unless you say it explicitly; in other words, these lights are fast if you don't need atmospheric shadows. Even with them, I'm working on a couple of algorithms to significantly speed the thing up, combining volume tracing [3] with Crow's shadow volumes [4], and also via light source Z-Buffers (quite fast using an all-integer approach).

Underwater stuff

These use a high density blue fog to simulate water in a (very) simple way. They (very vaguely) reminded me of those SeaQuest submarine anims... hence the names.

The first scene includes a bunch of aligned little light sources (30x2). I've devised a new type of light source (well, at least I haven't seen it anywhere :-) which allows the inclusion of hundreds of them in a scene, without the time needed to render it getting close to the age of the Universe. I call them (lacking a better name) finite range fall off lights (FRFOL), or bounded lights, for short.

What about the other pictures? nothing special, they just look great... If you want to get into advanced underwater rendering, try [5], one of my favourite papers.


References

[1] Max, "Atmospheric Illumination and Shadows", Computer Graphics (Proc. of SIGGRAPH '86), 20, 4 (1986), pp 117-124

[2] Nishita, Nakamae, Okamoto, Kaneda, "Photorealistic Image Synthesis for Outdoor Scenery under various Atmospheric Conditions", The Visual Computer, 7 (1991), pp 247-258

[3] Inakage, "Volume Tracing of Atmospheric Environments", The Visual Computer, 7 (1991), pp 104-113

[4] Crow, "Shadow Algorithms for Computer Graphics", Computer Graphics (Proc. of SIGGRAPH '77), 11, 2 (1977), pp 242-248

[5] Nishita, Nakamae, "Method of Displaying Optical Effects within Water using Accumulation Buffer", Proc. of SIGGRAPH '94, (1994), pp 373-379

[6] Omura et al., "Object Modeling by Distribution Function and a Method of Image Generation", Journal of papers given by at the Electronics Communication Conference (ECC) '85, J68-D(4), pp 718-725

[7] Warn, "Lighting Controls for Synthetic Images", Computer Graphics (Proc. of SIGGRAPH '83), 17, 3 (1983), pp 13-21


Thanks to

Prof. Francisco Villatoro, from Málaga University (Spain), for many interesting image synthesis discussions and for providing me some good technical papers.

Jose A. Maese and Francisco Marquez, for their cooking skills (oh, my God, what a nice peppered steak we had!)

Carlos Jimenez, for his support and help with Unix and internetworking (hey, this man knows what he is talking about!), and for being such a cool guy to talk with about math and brains.


Marcos Fajardo, marcosfajardo@hotmail.com.

Last update: 25 March 1996 1