Linear/Area light optimizing techniques?

[leigh]

You can fake the soft shadow look with spotlights, however to get a decently accurate shadow that actually "clings" to the model edges, you have to have the shadow map size so high that the render times come close to that of area lights, which look better anyway.

You can try taking down the Area Light Quality setting in the lights property panel. By default this value is 4.0 but you can take it down to around 3.0 for many situations. This can decrease your rendertime a bit.

[Tabby]

Ah yes, i guess i could put spotlights to create shadows for the ceiling objects. Hmmm, does anyone know if the same shadow and lighting effects of area lights can be achieved in other 3D packages but with shorter render times? or does LW still rock!?

[leigh]

Area lights are slower than spotlights in all packages.

[Tabby]

Thanks Leigh. I just saw your website and stuff. It appears... you're a texture/lighting guru.
*i'm not worthy i'm not worthy!* :P

Anyway, are area lights like some kind of necessary evil? prior to area lights, was radiosity the only way to achieve the same look? Are area lights really used that much?

[Dave Jerrard]

What's the quality of your area lights? I almost always knock mine down to 3. It makes them slightly grainier, but that gets cleaned up quite nicely during the AA passes. In fact, if you used some pretty extreme AA levels, you could even get away with lowering them to 2.

4 and 5 are really only needed if you don't use AA, or you use the evil called Adaptive Sampling.


He Who Lights A Lot Of His Stuff With Area Lights With A Minimal Hit On Render Times.

[biliousfrog]

Anyway, are area lights like some kind of necessary evil? prior to area lights, was radiosity the only way to achieve the same look? Are area lights really used that much?

um, I think area light have been around much longer than radiosity:hmm:

maybe try a radiosity render instead...I can't remember the last time I used an area light, I generally stick to radiosity.....as for an alternative renderer, I can highly recommend Messiah:Studio....better animation, faster rendering & more control over surfacing.

[Tabby]

Initially i left the quality at 4, after initial renderings, i bumped it down to 2.

About using radiosity instead? i don't know the rules with using radiosity, but usually in my scenes, if i use just one light, and enable radiosity just to see what it's like, i never get to see the final render, i just cancel it, because radiosity to me is the king of all render times.

[Dave Jerrard]

There's two types of radiosity - backdrop and MonteCarlo - in LightWave. I know there's also interpolated, but that one tends to make a lot of blobby noise that looks horrible, and the it's only good for scenes were nothing moves but the camera.

Backdrop is just slightly slower than an area light and I've used it for a lot of stuff over the past couple years. If you have a machine that's in the 2Ghz range (preferably dual), radiosity isn't painful to use anymore.

One thing that I did found out last year is a bit of a surprise. On a shot that I was setting up with two area lights and backdrop radiosity, when I changed the backdrop to an HDRI map and turned off all my lights, the render times got much faster! Even faster than the scene rendered using just the area lights. Yep, Backdrop radiosity without lights was faster than using lights. And it was a noticeable change when I turned on Ray Trace Optimization, which only has an effect on area lights and radiosity. Rendering frames as 2k dropped from about 1.5 hours and up to under an hour.

Now what to watch out for... Backdrop radiosity doesn't handle transparency. It's really an occusion based simulation. In your scene, with light coming in through the windows, backdrop radiosity would not help, unless you separate the windows and make them Unseen By Rays. This is the only way to prevent an object from blocking radiosity so far. Unfortunately, it also means the windows will not reflect in any surfaces. You might be safe here.

This won't give you a lot of ambient light inside the building though, so you'll probably want to try MonteCarlo. This will respect transparency, and the single bounce it does by default will create some nice lighting.

Now, if you're not moving anything but the camera, try baking the radiosity. You'll need to make a UV map or two for the objects,and just bake the illumination. This will take a while, but if your UV is good and you have a large enough resolution, you'll only have to do this once. Then you can map that illumination map onto the object in the Luminosity channel turn off your lights (or make then specular only if you need highlights). The scene will render blazingly fast then, and look just like it did with radiosity turned on.


He Who Is Looking Forward To Seeing An Update.

[gerardo]

MotionBlur is your friend. You can achieve some interesting (and FASTER!) results with spinning lights, a technique created by this http://webpages.charter.net/djerrard/DJ-SP-10DPI.jpg freaking LW genius and automated by the brilliant Ekki Halkka in his Overcaster (now PlugPak):

http://www.kolumbus.fi/erkki.halkka/plugpak/

There you'll find an application called Innercaster, with it (and small modifications) I made this:

http://www.geocities.com/gerardstrada/testcath2.txt

The impressive modeling was made it by Limkinkwan and all lights are spotlights; is here in some CGTalk thread :)

Another option is to use the same spinning light trick principle with arealights (is even more ease), the advantage of this is you can use quality 2 and to obtain quality 5, just with moving, spinning or scaling your lights and some MotionBlur.

Another option (relly faster and easy to use) is SG_AmbOcc of the prolific programmer Skidbladnir :thumbsup:

http://www.cgtalk.com/showthread.php?t=167204

Some time ago I tested this shader for first time in this interior:

http://www.geocities.com/gerardstrada/testsala4.txt
(only with a couple of spotlights and that shader)

But for your case, I think this Duke's image is really impressive:

http://www.dukecg.net/PoliceBuilding_interior_A.jpg

You can use the shader directly in render or for further accuracy you can use refvector_CamDirection option and to bake the shader in the textures.

(Btw, at the moment I'm working in a technique to use an ambient occlusion maps precomputed as spotlights shadows, I hope some shaders developer finds this idea interesting)



Gerardo

[Tabby]

Holy S#^T! who'd have ever thought about motion blurred rotating spotlights! is there a tutorial on this technique somewhere?

[duke]

Follow the yellow brick road to Dave's site.

It's better expressed with pictures, but the basic principal is that if a light (or anything really, the spinning trick in general has been put to good use) is pointing in one spot and casting a shadow in frame 0, and is in another spot at frame 1, with motion blur on it will blur between these two motions, although it will be stepped (if 4 passes, 4 steps between them and so on). There are numerous ways to work with it, for instance having more lights, therefore the distance between the motion is shorter because you have 2 lights covering that complete motion instead of 1.

To make an area light out of spotlights, you'll need to create an array of spots (start with 4 and go from there), and animate the cone angle between frame 0 and 1 with motion set to repeat, which will give you your soft edges when it motion blurs.

[biliousfrog]

hehe.....nice to know that in a world of radiosity the spinning light trick still impresses:)

I've used it a lot for animations when motion blur is normally on anyway & radiosity would take waaaaaaaaaay too long. You need to get the rotation amounts right with the motion blur, AA & frame rate.....I normally stick to 30fps, rotations at 720 per frame, motion blur at standard 50% & AA at medium. Of course there's a formula for working out other settings (which I can't remember) & with more AA options in 8.2 it might be worth knowing how to adjust your settings to compensate.

Of course you're not stuck to using spinning lights.....the same principle can be used to moving lights. For a large warehouse or aircraft hanger you could set up a row of spots along one side of the ceiling & have them move to the other side over the course of a frame.....this gives a very good approximation of the lighting used in industrial areas, where there are often many strip lights covering the ceiling.

[duke]

You could even use fractional frames (still using a total of 1 frame) and move them across as many rows as you want if you're nuts!

[Dave Jerrard]

MotionBlur is your friend. You can achieve some interesting (and FASTER!) results with spinning lights, a technique created by this http://webpages.charter.net/djerrard/DJ-SP-10DPI.jpg freaking LW genius


DAMN that's scary! Had me laughing too. I was kinda freaked out about how you got that full sized image. Then I remembered the other post.


Nice renders by the way. Amazing what Over/InnerCaster is capable of.

He Who Is Watching Some Of The Weirdest Stuff On TV Right Now.

[Dave Jerrard]

Follow the yellow brick road to Dave's site.

That is, when I get a new one up. Haven't had any time to work on an update lately.


He Who Has A Lot Of Updating To Do.

[gerardo]

DAMN that's scary! Had me laughing too. I was kinda freaked out about how you got that full sized image. Then I remembered the other post.


Nice renders by the way. Amazing what Over/InnerCaster is capable of.

He Who Is Watching Some Of The Weirdest Stuff On TV Right Now.


Hehe. Yes, Ekki's spinning lights rigs are excellent and a good starting point for more elaborated rigs; in the previous case I made a slight modification to his Innercaster rig and I separated the geometry in square modules (because this type of rigs works better this way).
I should suppose that the spinning lights principle is the most useful and the technique more used in the history of LW, its applications are endless, but isn't always something easy to figure out since we should think in 4 dimensions.
Btw, thank you for your comments and thank you very much for this ancient Spinning Light Trick article:

http://www.mohhs.com/lw/pdf/
(that I was searching for years) :)



Gerardo

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