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Eclyps19
07-18-2005, 11:05 PM
2 parts to this.

a) For some reason my caustics aren't working correctly. I can have a transparent cup, lets say.... green.... refractions and all that are set good, cup looks great, but no caustics. =( makes me quite upset....

b) Why the hell are there still no ideas on creating realistic gem surfaces. I can never get anywhere even remotely close... you'd think that after 3 years i would be able to but no. Someone please help me out here... thanks

cyphyr
07-18-2005, 11:45 PM
Hi
Caustics is a bitch and I dont know any program that dose it well, I'm no expert but here are a couple of tips that may help.

1 Distant light type dont work.
2 The distance the caustic casting light is from your object makes a difference.
3 While your setting things up ...
keep the accuracy low.
make your "glass" unseen by camera.
4 Caustics are effected by very small vairations in the "glass" structure; a very fine bump map or displacement map will help here.
5. As always take a snap of a glass casting some real caustics and keep in near for reference.
6. The annoying speckly effect created at high accuracy settings can be removed by parenting the light to a null targeted at the "glass", offsetting the light slightly and spinning null 360 deg every frame. Set the camera to render motion blur and run at least 9 passes of AA. This will take a long time so it may be better to run the caustics as a seperate pass and then use thar as a surface beneith the glass.

Hope this all helps, post some wip and your results :)
cheers
cyphyr

Panikos
07-19-2005, 01:01 AM
http://vbulletin.newtek.com/showthread.php?t=24302&page=1&pp=15&highlight=Caustics

I wish I had the time to write more on caustics, too busy

:love:

TheAlfheim
07-19-2005, 07:12 AM
When I was playing around with caustics a while ago, I found that the size of the object mattered.

If I'm just playing around, I dont worry about size/scale. So I'd make a glass which was a few meters tall. Caustics wouldnt work. If I sized it down to something a little more realistic (200mm, say), it would work.

Maybe the size of the object has something to do with it?


Cheers,
TheAlfheim

Exper
07-20-2005, 05:08 PM
LW's caustics are really sensible to objects/scene size and they're the most weak part of the rendering engine. Though they can provide good results are quite difficult to setup correctly and they're really slow.

Don't use the same light for Illumination and Caustics. I always use separate lights (at the same position if I need the perfect correspondition) so I can adjust both Illumination ad Caustics at the same time in a total flexible way.

Another good habit is to put the Caustics-lights near the object (as near as you can).

This is screen-grab of a Caustics testing scene of mines:
http://exper.3drecursions.com/lw/c_lights.gif
You can see the rendered scene here: A Little test about Caustics (http://3drecursions.com/forum/viewtopic.php?p=90#90) (the third one).

If this approach is not possible due the scene Illumination then try to find a good compromise (easy to say... difficult to do).

Experiment with Intensity value and don't be afraid to go up to 2000/4000% (these values are really funny).

You can blend the sharp results... use a combination of Accuracy/Softness values; in most cases I found myself good with 300/100 and using the spinning trick already reported by cyphyr.

Hope it helps.

gerardo
07-21-2005, 03:37 AM
I agree with Exper, size is important with LW Caustics. About Gems surfaces, take a look at this ancient tutorial (http://www.mohhs.com/lw/pdf/Gems.pdf) (the principles are also now the same ones).
Some time ago I made these tests:

http://www.geocities.com/gerardstrada/Gem.txt

with that tutorial and with Daniel aka Da_Duke's technique of chromatic aberrations, who takes this tutorial further on using an envelope in refraction index (as Jerrard's spinning light trick) and changing the color of the object-gem in each pass.
The advantage of this technique is you have complete control over the colorations in chromatic aberrations.
If you want to obtain the difraction effect (prism effect) you can use this technique (http://lw-fin.org/tutorials/asa/prisma/tutorial_prisma.html) based on the same principle.

Aurora has very nice presets (http://www.auroragrafx.com/LWresources/LW_Presets/GemStones/Presets_Gemstones.shtml) as well; I got this with his presets:

http://www.geocities.com/gerardstrada/Presetsgems.txt




Gerardo

Eclyps19
07-23-2005, 03:07 PM
those look great. I still duno how you got something as good looking as that though, even with the tutorials i'm still a bit lost. That one tutorial about the colored light was a bit confusing too... hmmm i guess i'll just have to keep messing with them...thank you

INFINITE
07-23-2005, 06:21 PM
I agree with Exper, size is important with LW Caustics. About Gems surfaces, take a look at this ancient tutorial (http://www.mohhs.com/lw/pdf/Gems.pdf) (the principles are also now the same ones).
Some time ago I made these tests:

http://www.geocities.com/gerardstrada/Gem.txt

with that tutorial and with Daniel aka Da_Duke's technique of chromatic aberrations, who takes this tutorial further on using an envelope in refraction index (as Jerrard's spinning light trick) and changing the color of the object-gem in each pass.
The advantage of this technique is you have complete control over the colorations in chromatic aberrations.
If you want to obtain the difraction effect (prism effect) you can use this technique (http://lw-fin.org/tutorials/asa/prisma/tutorial_prisma.html) based on the same principle.

Aurora has very nice presets (http://www.auroragrafx.com/LWresources/LW_Presets/GemStones/Presets_Gemstones.shtml) as well; I got this with his presets:

http://www.geocities.com/gerardstrada/Presetsgems.txt




Gerardo

WOW Gerardo, they look beautiful!!

gerardo
07-24-2005, 06:54 AM
Thanks Infinite! :)
Eclyps19, that tutorial is probably a little confused, but Aurora's presets comes ready to use (with a list of refraction indexes and Ray_Recursion_Limit for each material). Remember the surfacing is only half of the result, the other half is provided by an interesting environment what to reflect. Try with a HDRI for reflections (in Imageworld or Textured_Environment as it's the case).
Btw, I've just found this link (http://www.3dlapidary.com/HTML/Models.htm) posted by RPG2004, there you will find an extensive gallery of very nice gems models :)




Gerardo

Panikos
07-24-2005, 07:02 AM
Slightly ON-topic, generally I never render with more than 4 ray recursions. Four recursions provide raytracing, shadows, reflections, refractions. Increasing this value slows down the rendering apparently.

For such needs though, where the attraction point is caustics, reflections, refractions etc in closeup shot, increasing the RCs is a must.
I dunno how other apps treat caustics, but according to what we have, is what we do.

Eclyps19
07-24-2005, 03:20 PM
how many other lights did you use in your scene?

And is that nice little glow a post render photoshop or somethin?

Eclyps19
07-24-2005, 08:07 PM
http://www.johnnystevenson.com/diamond.jpghttp://www.johnnystevenson.com/tanzenite.jpg


These are as close as i was able to get. Any suggestions on how they could be improved?

blaqDeaph
07-25-2005, 12:02 AM
Try cranking up reflection/refraction, and setting a high refraction index.

What are your current surface settings?

gerardo
07-25-2005, 12:43 AM
how many other lights did you use in your scene?

And is that nice little glow a post render photoshop or somethin?


In that case the lights have little influence in the final result; I only used one light (without shadows) since the effect is really provided by the environment. If I don't remember wrong, for the first group I added the glow effect and color correction in post, and I used Corona (ImageFilter) for the second group.
I think you almost got it, maybe you want to check some things:
Revise that your object-gem also has an inward-facing "air" surface (flipped polygons) as is explained in Dave Jerrard's tutorial; this is very important to represent the light behavior correctly in its refraction with the surface.
If you are using specular, before adding an environment or HDRI, first check your light provides nice specular highlights in your object, trying to maintain moderate levels; you can do this in OpenGL view.
If you want more saturation in reflections, you can increase Color_Filter percentage.
If the radiance levels of your HDRI are very high (white wide areas), you can limit the dynamic range with HDRExposure (Image Editor/Processing/Filter)
Remember if you are using a HDRI, you may rotate it until finding a position that offers you more interesting reflections.
For the glow effect you can use Corona or BetterBloom (this filter is excellent for animation) or to do it in a composition software :)



Gerardo

Eclyps19
07-25-2005, 02:48 AM
i am using the flipped poly (air) thing. I guess i am just going to have to keep messing around with stuff... its getting a bit better but maybe once i find some better HDRI images i'll get some better results. thanks for all the help

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