Spotlight shadows

[mechis]

Hi Everyone,

I'm trying to learn how to light scenes in xsi and have a few questions for you.

1) If I'm lighting with spotlights, is it possible to have raytraced shadows that get blurry as they go further away from the object, without turning on area lights? It seems that if I have raytraced shadows on (and no area light), I can only get a hard edged shadow.

2) In the picture I attached, I have a spot light with area lights turned on. As you can see, the shadow is noisy as it hits the wall and that is something I can't seem to get rid of. What settings do you think I should be changing? All I can find that might affect this is the shadow's U and V sampling and they don't seem to do anything.

3) In Maya, there's a "Raytrace Shadow attributes" dialogue that has settings to control the quality of the shadow. The settings are-- light radius, shadow rays and ray depth limit. What would be the equivalent in xsi? I've been reading the docs and going through the panels in xsi and can't seem to find these settings.

Thanks,
~Mechis

[mechis]

I've been reading online and also experimenting... it seems that you can't have raytraced shadows that are smooth, unless you use area lights.

What is the usual sampling level that people like to use for area lights?

Do most people like to light with area lights for their more realistic shadows? Or do they just use shadow maps?

If you use shadow maps, is there a way to make the result look more realistic than simply a shadow that has been blurred all the way around?

Thanks,
~Mechis

[CiaranM]

Hi,
The only way to get really accurate soft shadows is with area lights. I really like to use them myself, as shadow maps are no good substitute if there are ground contact shadows involved.
You're right to adjust the u,v area light samples, that will increase the quality of the cast shadows as well as shading from the area light. However, your anti-aliasing settings will also help clean up the noise.
Generally, I might adjust my aa settings to suite the rest of the shot, then would increase my area light samples to remove excessive area light noise. I might then tweak the aa (lower the sampling threshold) for a little extra help. However, adjusting the light samples will be more efficient as it effects only those parts of the frame illuminated by the light, whereas aa sampling is for the whole frame.
The area light samples really depends on the size of the light and the softness of the shadows. Once it gets too big, you'll need to ramp up the samples.
Mental Ray area lights aren't perfect, and there might always be a little bit of noise - which often is not noticeable on a textured surface. If your area light is too huge, you might consider using Final Gathering and an emitter object instead of a light.

There is no shadow depth setting in XSI. Reflection and refraction and global trace depths are controlled in the MR render settings.

[mechis]

Interesting stuff, Ciaran. Thanks for the info. The main reason why I was resisting area lights is b/c in the wiki it said they were cpu intensive and should only be used as a last resort... it seems like they are the only way to get nice and accurate soft shadows though.

I also didn't realize the effect that aa had on the shadow... I'll definitely have to experiment with that.

Thanks a lot!
~Mechis

[JDex]

Hmmm... while they are cpu intensive, if you do a good job optimizing your scene, there's no reason that you can't use area lights where ever you need them, even if you need alot of them.

Keep the samples as low as you can get away with... render the shadows as a separate pass, optimize the aa and bsp as best as you can and render times should be acceptable in most cases.

[mechis]

Thanks jdex... the optimization tips are great to know! I'll definitely remember to do this while I practice my lighting.

~Mechis

[kim aldis]

The main reason why I was resisting area lights is b/c in the wiki it said they were cpu intensive and should only be used as a last resort...
~Mechis

I wouldn't say that intensive, although you should do some tests before considering their use with hair. Area lights kill hair renders.

Render times are more or less dependant upon how much softness you introduce into your shadows and the apparant softness depends on a combination of light size, distance from shadow of light and camera distance from shadow. Unless you start going for really large soft shadows render times should be reasonable.

if you go for shadow maps try and use spot lights, you'll get better results.

[mechis]

Thanks Kim... it was your article on the wiki that I was looking at. Re-reading it, I realized that the big time jump was from area lights + hair. I guess if I'm not using hair and am careful with how soft the shadows are, I should be good.

~Mechis

[kim aldis]

Thanks Kim... it was your article on the wiki that I was looking at. Re-reading it, I realized that the big time jump was from area lights + hair. I guess if I'm not using hair and am careful with how soft the shadows are, I should be good.

~Mechis

I didn't realise that piece was on the wiki. Yes, it's just hair really.

In general, what you consider reasonable rendering time is up to you, it'll vary according to need, production, production schedule, resources ... The most important thing is to test and keep tabs on what render times are becoming throughout your project so you don't get caught out at the last minute.

And learning how to optimise, of course.