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View Full Version : Soft shadow edges needs hundreds of rays?


JohnP10
08-10-2010, 02:20 AM
I'm finding that when I use ray tracing shadows in MR, in order to get a decent/realistic soft edge to shadows, I need to make the shadow rays about 400ish. This seems excessive. Am I missing something?

Wouldn't it make sense for MR to give you an option to blur the 'grainy' result instead of having to pour hundreds of samples into a light to get a smooth result??

What are typical settings for the light, shadow and render globals to get a decent soft shadow?

Thanks

Dangertaz
08-10-2010, 02:45 AM
For soft shadows I typically use a large area light set to 20 Rays with a ray depth of 5. It's grainy but then I set my AA Max Sample level to 2 and that cleans it up quite a bit.

InfernalDarkness
08-10-2010, 05:39 AM
For preview renders I use 8, and for finals generally 16 (or less if possible). What kind of filtering are you rendering with? What kind of sampling?

Any specific light you're talking about? I think for the most part Final Gather and/or GI smooth out the shadows anyway, and if you're using indirect lighting like that it really helps blend the raytraced shadows.

ndeboar
08-10-2010, 05:41 AM
if it's a REALLY soft shadow, look into directional occlusion, you can similar results using a lot less samples.

JohnP10
08-10-2010, 08:36 PM
Okay, here's a few renders. For all I have Production Quality set in render globals. I rendered them all at 960x540, but had to halve their res to upload them, so sorry for the squinting!

On the Directional Light image I have a light angle of 30 and 40 shadow rays. You'll notice the soft shadows are very chunky. I have reflective MR mia materials on the back wall and floor, but even with a lambert room it is still very chunky. (So it's not reflection related...)

On the MR Area light (the one with the big hotspot) I have 16 shadow rays and 16 high samples on a sphere shape light which I scaled up (all low samples are set to 2 on all three renders btw). This image has very grainy results also. (I'm also still searching for a way to hide the hotspot in reflections btw)

On the last image I used a spot light converted to MR area light and put it outside the window and scaled up. I made the room a lambert shader. I had 30 Angle, 16 Rays on the shadows, and a rectangle type with 8 in high samples on the light. This took 6 min to render at 960x540 on a brand new i7 (fastest 4 core processor hp offers). It's hard to see because I down res'd, but even this appears very chunky, especially around the mid tones/shadow edges.

Isn't this render time a little excessive (and still less quality than I'd like) for a simple 1 light scene with 2 objects? Not to mention FG and GI aren't even turned on...

I'm working in television and am outputting for HD 1920x1080 (or at least 1440x810). I don't expect the highest quality, but is there is some sort of acceptable compromise where animations can render @ about 10 min a frame? Am I asking for too much?

@Dangertaz - 'AA Max Sample level' is that the raytrace quality in the render globals you're referring to?

Thanks

Dangertaz
08-10-2010, 08:48 PM
I meant Quality>Anti-Aliasing Quality>Max Sample Level under the Render Settings.


Try making your area light a rectangle and setting the high samples to 100 with the high and low sample limits to 50.

Within the mia material, towards the bottom is an "advanced" tab and within that is a control for "Specular Balance", turn it to zero to eliminate the hotspots.

InfernalDarkness
08-10-2010, 08:58 PM
On the Directional Light image I have a light angle of 30 and 40 shadow rays.

Sun/sky? You should be using a portal light here, period.

On the MR Area light (the one with the big hotspot) I have 16 shadow rays and 16 high samples on a sphere shape light which I scaled up (all low samples are set to 2 on all three renders btw).

Portal Light.

On the last image I used a spot light converted to MR area light and put it outside the window and scaled up. I made the room a lambert shader.

You should be using an area light set to mental ray area light, and again: Portal Light.

I see what you're trying to do here, but you need to be using the Portal Light for scenes like this. I just watched a spectacular video (try and dig up the link for you) explaining exactly why the Portal Light node works so well, and to sum it up: the portal light helps FG smooth out the scene by concentrating the FG rays so that they return the actual lighting, instead of an average of the lighting points spread throughout.

If you're using mental ray for interiors like this, you should be using the Portal Light instead of these other deprecated lighting methods. Your render times can be decimated (1/10th) if not better, and your results will be far, far smoother and more realistic.

JohnP10
08-10-2010, 09:20 PM
Thanks for the info and the quick reply guys.

Got rid of that hotspot, so thanks for that Chris.

I was trained as a games artist, so lighting and MR are (obviously) not my strengths. How do I go about hooking up a portal light (or any other MR light node...) Any tutorials you know of would be great.

@InfernalDarkness - So a portal light is the go for shining in from outside, but you're saying it's still best for a general 'lets brighten the room' situations also? I like this 1/10th talk, what other 'crap' lights should I always avoid?

InfernalDarkness
08-10-2010, 10:37 PM
@InfernalDarkness - So a portal light is the go for shining in from outside, but you're saying it's still best for a general 'lets brighten the room' situations also? I like this 1/10th talk, what other 'crap' lights should I always avoid?

It's not so much that they're "crap", although I see where you're coming from, but try to pull off smooth shadows in Maya software: you'll end up using roughly the same render-intensive settings.

The Portal Light should be used for any interior scene with any lighting, but of course in some cases you'll need point lights and spot lights for various real-world lighting types. I don't use them for, say, lighting fixtures, but I probably should/could.

The Portal Light's function is to basically create ACTUAL light in the scene for the Final Gather to pick up on and work with... Here's the video I was talking about; it's WELL worth watching in its entirety; you'll learn a great deal about how mental ray works, too, and it's simple and funny enough to still make sense.

Maya/mental ray: Portal Lights (http://vimeo.com/8424293)

JohnP10
08-11-2010, 02:39 AM
Thanks for the great link. I think I just quadrupled my MR knowledge... :beer:

Looks like there's a whole bunch of stuff there... (Lots of learning to be done!)

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