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ShawnStovall
04-19-2006, 08:19 PM
I would like to know a little bit more about radiosity because I can't figure out how the stupid thing works. I have done several different tests and I just can't see the difference. I would like to learn how to use it because I have seen some great things done with it.

Thanks a lot for your time!:thumbsup: :lwicon:

wongster
04-19-2006, 08:26 PM
hi.
If you cannot see the difference, maybe the object / surface doesn't show much difference.
I can explain what radiosity is. In the 3d world, light hits an object and illuminates it. You know how in real life light bounces? Well with radiosity, a surface that would normally not be in direct light, (such as the bottom of a table) is lighten up by "bounced light". Without radiosity, you can still see the bottom of the table, but this is only because of global lighting.

ShawnStovall
04-19-2006, 08:35 PM
Any tips on using it?

Captain Obvious
04-19-2006, 08:43 PM
http://www.newtek.com/products/lightwave/tutorials/rendering/fullprecision/index.html#3

This entire article should be read by anyone doing 3D graphics. There is a little bit about radiosity in LW.


http://www.winosi.onlinehome.de/Gallery_t5.htm

The image on the left on that page uses "radiosity," while the image on the right doesn't. Which do you think looks better? ;)


http://graphics.ucsd.edu/~henrik/images/cbox.html

Scroll down to Ray Tracing, Photon Mapping, and Global Illumination.




Edit: also, check THIS (http://tegelstenclothes.mememachines.net/randomcrap/krayKitchenIrrCache.jpg) out. I rendered that with just one area light for the sun and a bright sphere around my scene. There are no lights in the windows, there is no ambient light. All the nice and soft shadows are there because of global illumination. It should perhaps be noted that I rendered this in Kray, and not Lightwave, but still. I think it's a good example of what global illumination can accomplish and why you'd want to use it. So, what's the downside? The render time for that image was over three hours...

ShawnStovall
04-19-2006, 10:47 PM
WOW! Radiosity is great! I have finally found the lighting tool I've be looking for. Before I couldn't understand how people got such realistic lighting but now I do. The only downside to radiosity is that it take forever to render. I just made a scene with just a box and a ball and it toke me about two minuets with Monte Carlo(which isn't too bad)and about fifteen with interpolated! With regular rendering it only takes about 0.2 seconds! Other then the amount of time it takes, I really like radiosity.:lwicon:

Yamba
04-20-2006, 12:23 AM
Hi Captain Obvious,

Your "THIS" render is beautiful thanks for attaching and thanks for the links very useful.

Yamba
Mac since IIe and still, well almost, sane.

starbase1
04-20-2006, 02:30 AM
Agreed 'this' is an awesome image.

And Shawn, I hope this does not worry you, but that is VERY quick for a radiosity render! :) (The last image I rendered with radiosity took 14 hours at 1600x1600 pixels!)

But as you have discovered, careful choice of parameters makes a huge difference. It's always worth experimenting with a smaller version of the image, (or a smaller part of the big one). Shading noise rediuction will also often improve quality without increasing render times, by smoothing the shadows.

When you have an imqage you really like, it's often best to set it rendering as you go to bed and hope it is done when you wake up. (Though I think my longest ever still image render was something like 24 days! Long time ago now...)

Captain Obvious
04-20-2006, 06:55 AM
Thanks :)

Anyway, now some practical tips regarding "radiosity" in Lightwave:

It's called radiosity, but it's technically not. Radiosity is a method of global illumination, but not actually the method Lightwave uses. Oh, I'm going to abbreviate some words: GI means global illumination. It's a collective name for rendering where light bounces around. Light comes from everywhere, hence the name.

LW has two modes of global illumination: monte carlo and interpolated.

The monte carlo mode is a brute force method. The global illumination is calculated independently at every single pixel. Since the result will vary slightly from each pixel, there will always be a certain amount of noise in an image rendered with monte carlo GI, unless you render with insanely high settings. The other downside of monte carlo is that it takes a long time to render, especially with multiple bounces. Every additional bounce will effectively double your render times, and even with one bounce, monte carlo is really slow. The advantages of monte carlo is that it's really easy to set up (just turn it on and hit render, essentially), and that it produces wonderful results. You'll never see render errors (blothces or light leaks, for example) in an image rendered with monte carlo GI, and the shadows are never washed out.

Interpolated GI is similar, yet very different. Instead of calculating the GI at every single pixel, it calculates it here and there, and then interpolates the result to fill the gaps. The samples are taken closer together in areas of higher detail, so that shadows won't get washed out, but this is far from perfect. Interpolated is really fast (and it slows down much less with multiple bounces than monte carlo; you can often use three bounces without much of a speed-hit), but it often produces big blotches and light leaks and washed out shadows, and this requires a lot of effort to tweak away. Another problem with the interpolated mode is that it will flicker in animations. This means, unfortunately, that Lightwave has no animation-friendly global illumination at all: monte carlo looks great, but takes too long to render; and interpolated will either flicker or take just as long to render.

JML
04-20-2006, 07:15 AM
Thanks :)
Anyway, now some practical tips regarding "radiosity" in Lightwave:

It's called radiosity, but it's technically not. Radiosity is a method of global illumination, but not actually the method Lightwave uses. Oh, I'm going to abbreviate some words: GI means global illumination. It's a collective name for rendering where light bounces around. Light comes from everywhere, hence the name.


I disagree,
in LW and some other softwares,
GI is a skydome emitter that doesn't bounce light.
like "backdrop Only" 'radiosity' in LW.

montecarlo and inerpolated is (slow) radiosity, it bounces light, emited from a skydome/backdrop or directly from lights.

Captain Obvious
04-20-2006, 07:19 AM
Now, here are some practical advice for using interpolated GI in Lightwave:

First off, let's look at the different settings:

"Cache radiosity" doesn't really do anything. Ignore it.

"Intensity" lets you control how much the GI affects the lighting. It's essentially the same thing as the global light intensity, but for indirect lighting. I generally recomend turning this up a bit, to 150% or so, but you don't have to do that unless you feel the scene needs more light.

"Rays per evaluation" controls how much splotchiness you get. If you turn render an image with monte carlo GI with a too low RPE setting, you will get noise. If you turn it up, the image becomes smoother. If you render an image with interpolated GI with a too low RPE setting, you get horrible blotches. Turn it up to smooth it out.

"Indirect bounces" is exactly that. More bounces means the light bounces around more times, filling out the scene. In interpolated mode, you can usually get away with setting this to 3, but you may need to turn it down to save on render times.

"Tolerance" controls how far apart the samples are taken. If you leave this at the default of zero, samples are taken everywhere, and interpolated will be just like monte carlo with all that comes with it. This is the primary thing you need to tweak. Set it to 1, and everything becomes washed out. Set it to 0.01 and the render time is too long. Getting this setting right is hard work, and it takes experience.

"Minimum space evaluation" controls the minimum distance between two samples. If this setting is too high, you won't get enough samples in high-detail areas, resulting in washed-out shadows. If you set it too low, render times go high. Again, this is something that needs tweaking.

Now, some practical down-to-earth tips for using interpolated in Lightwave!

First off, turn on motion blur! I cannot stress this enough. Rendering with interpolated NEEDS motion blur. Essentially, what this does is that it calculates the global illumination several times and then averages the result. It increases the render time by almost nothing, and increases quality a whole lot. Secondly, you might want to turn off ambient light. With both ambient and GI, an image often becomes washed out.

As for the settings, they're highly scene-dependant. But you might want to start with setting the RPE to 6x18, the bounces to 2, the tolerance to 0.4 and leave the minimum distance at the default. If you find that your shadows are washed out, try reducing the minimum distance. If you feel that you get too much blotchiness, try increasing the RPE slightly. And then, see how much you can reduce the tolerance while still getting good render times. Finally, turn on at least enhanced medium anti-aliasing and render. This will take exactly nine times longer than a render without anti-aliasing.





Also, there are a couple of better ways of getting good global illumination renders in Lightwave: Kray and Fprime. They're both plugin renderers, and both handle GI much better than Lightwave's standard renderer.

Captain Obvious
04-20-2006, 07:29 AM
I disagree,
in LW and some other softwares,
GI is a skydome emitter that doesn't bounce light.
like "backdrop Only" 'radiosity' in LW.

montecarlo and inerpolated is (slow) radiosity, it bounces light, emited from a skydome/backdrop or directly from lights.
Global illumination is a collective name for rendering technologies that allow for diffuse-diffuse interactions, like irradiance caching, MLT, etc etc etc.

Edit: Oh, right, I got my words mixed up. Radiosity is just, well, light bouncing.

ShawnStovall
04-20-2006, 10:04 AM
Where can I find Kray?

mattclary
04-20-2006, 10:14 AM
http://www.kraytracing.com/

You should also go here:

http://www.worley.com/fprime.html

Rendered with FPrime and radiosity:
http://www.newtek.com/forums/showthread.php?t=26754

http://www.newtek.com/forums/showthread.php?t=26352

ShawnStovall
04-20-2006, 10:25 AM
I checked out both and they are very expensive! I can't afford either of them. Does anyone know where I can find a high quality renderer for free?

-Thanks-

Ztreem
04-20-2006, 11:04 AM
I think Lightwave has quality enough, it can be a little slow with radiosity becuase some lack of methods like final gathering and such, but I don't think you should get stuck with using only radiosity. Sure it's a nice thing and I like it a lot, but it's not impossible to make realistic renders without it. Here's an example of two different renders of the same scene with almost the same result. I made this a while back just to show it's possible to fake radiosity and you can gain a lot of time using it.

JML
04-20-2006, 11:07 AM
nice test Ztreem :thumbsup:

Ztreem
04-20-2006, 12:24 PM
JML: Thanks!

Here's an other one, this render doesn't even have shadows in it, even if looks like it. :D

Captain Obvious
04-20-2006, 12:38 PM
I checked out both and they are very expensive! I can't afford either of them. Does anyone know where I can find a high quality renderer for free?

-Thanks-
http://www.kraytracing.com/

There's a free demo available for non-commercial work. It has no limitations other than a "demo version" watermark that doesn't take up much space. But beware: Kray is NOT the easiest renderer to use.

mattclary
04-21-2006, 05:29 AM
Yeah, $399 ain't cheap. I think I bought it originally for about $249 when it firts came out. Whatver I spent, it was well worth it. As soon as you can afford it, I encourage you to get it, it's truly awesome.

ShawnStovall
04-21-2006, 08:44 AM
Opinions on Fprime?

Captain Obvious
04-21-2006, 09:36 AM
It seems really fast and good. It's probably a huge timesaver when setting up textures and lighting.

ShawnStovall
04-21-2006, 04:34 PM
How do I do the lighting for a Radiosity box?

Captain Obvious
04-21-2006, 04:44 PM
You mean a cornell box (http://graphics.ucsd.edu/~henrik/images/imgs/cboxgi.jpg)?

Intuition
04-21-2006, 07:01 PM
F-Prime is super fast. You can make changes and see them instantly.

Some say its pricey, others don't, but in my opinion it is a must have for anyone using Lightwave.

You want to do radiosity and do it fast then F-Prime is the way to go.

Kray is very good as well. Its also free to try out so you can learn as you go.