rendering hair (xsi hair - not ice) with ibl

[fjg]

I'm trying to render hair with image based lighting and it seems to always come out very grainy. Not the best example, but this is what I'm
talking about:


There is probably a 'sample level' that I haven't set high enough, but I'm not sure
where. I've adjusted the lights themselves quite a bit already.

Any ideas on how to sharpen up the details on (shave)hair?

thanks

EDIT: btw, I'm using the hair gradient shader, but any shader suggestions welcome...

[swann]

Use DeepShadows on lights instead of ratraced onses and set MR to rasterize mode.

[fjg]

A better example of the render issue:


I've tried various shader (all with normal blend set to 1) and light types, but the hair is still rendering strangely.
Each strand segment is rendered without regard for its neighboring segment.
I'm using kh3 hair here, but this happens with xsi hair and other strands...

Is it possible in this case that is getting uv's incorrectly?

EDIT: edited the title

[rray]

What is your lighting setup?

[fjg]

The last render is a couple of portal lights, top and front, and a point in back.

EDIT: Also, the shader uses a ray switch to combine a hair shader and lambert.

[rray]

If it's possible I'd work with a light rig built from the image, and a normal hair shader (internal "Hair_shading" or muh_hair). This will be much faster. Hair+area lights is the slowest it gets.

Don't know if it's the shader that causes the artefacts, I've seen something similar when not using "segment" shapes for the points - although you wrote you get them with normal hair, too.

[fjg]

thanks for the tips, I'll give it a shot.

[rray]

Found that out recently... a good compromise between speed & quality is also using mental ray's internal IBL lighting accelleration (can be enabled with the Ctrl_Ghost_Settings geoshader).
(Tip don't use approximate mode if you want realistic highlights)

[rray]

Here's a hair test btw, rendered with MR's IBL accelleration.
Ca . 10 hr but no render settings tweaking, max IBL quality.
Would need stronger specular settings and some thickness+length gradient for a more realistic hairline

rr_hair_ibl.jpg

[fjg]

Hey this looks really cool - I haven't been able to get anything like this. Is it possible to post the file so I can deconstruct it and find out what I'm doing wrong? I wouldn't need the geo, just the hair cloud, lighting, and render settings... I took a look at your other file (with the cube) and it does render better that what I've been able to get - is it done with same settings as this image?

I guess my next question is would you render a character skin on a different pass (with portal lights) and comp the hair rendered with light-rig in post? or is that a nightmare? I like how the portal lights and ibl look on the skin, but as you pointed out earlier, it is slooooow.

Thanks!

[Mathaeus]

I guess my next question is would you render a character skin on a different pass (with portal lights) and comp the hair rendered with light-rig in post? or is that a nightmare? I like how the portal lights and ibl look on the skin, but as you pointed out earlier, it is slooooow.

I'd say, not a nightmare. If you're already with this, maybe it's good idea to use a low-res hair for 'body pass', setting the hair only as a shadow caster, invisible to primary rays. In "hair pass", matte material for body.
Anyway, this requires a good bit of work, just to "match" the look of both. So many images on internet (cgTalk and so) suffers of this "mismatch".
Now I always trying to use the same lighting setup, as well as one render pass for whole character - in 3delight.

[rray]

Hey this looks really cool - I haven't been able to get anything like this. Is it possible to post the file so I can deconstruct it and find out what I'm doing wrong? I wouldn't need the geo, just the hair cloud, lighting, and render settings... I took a look at your other file (with the cube) and it does render better that what I've been able to get - is it done with same settings as this image?

I guess my next question is would you render a character skin on a different pass (with portal lights) and comp the hair rendered with light-rig in post? or is that a nightmare? I like how the portal lights and ibl look on the skin, but as you pointed out earlier, it is slooooow.

Thanks!

It's a different setup than that, it uses IBL lighting (Which works great too with the fast skin shader btw.. combination should work fine too)

Process is
1. download & install

Ctrl.Ghost.Settings.xsiaddon.zip

2. get primitive geoshader, apply the ctrl_ghost_settings to it
3. Inside, turn on the IBL lighting option with "transparent" shadows
4. create a pass environment, set default light to intensity 0
5. There's a bug, it doesn't render right away, only for the second time, so press f5 to refresh render region/add an extra frame in front of a sequence

I'll put something together if I find some time.

[Kzin]

try to render with unified. with this you can set the ibl quality to 0.2 and unified with min1/max100 and quality 5 or 10 as starting point. if you have grain in your render increase the max sampling of unified, not the ibl quality. i never use ibl quality of one, its to slow at the moment with adaptive and with unified not necessary.

[fjg]

Thanks for the replies - I'm testing each suggestion.

rray - does brute force final gather in ctrl.ghost need to be turned on? What about the progressive settings - do they work in si?

Thanks!

[rray]

Kzin, thanks for the tip. I tried Unified with Rasterizer+IBL but got stripe artefacts with low IBL quality settings.
But got a 5-10% speedup for the Light rig+shadowmap render, without quality loss. Have yet to try Scanline+IBL+Unified but am guessing that it'll be too slow. Light rigs+shadowmaps for IBL still seem to be the way to go, even though it would require a pass setup because normal (non-hair) shadows have too much artefacts with that setup.

fjg, brute force FG isn't needed unless you want high quality (uninterpolated) FG results. Progressive works fine, but only with mia_material (not even with "Architectural" even though it's the same basically). Using textures logs an error, but it renders fine using a Projection_Lookup in mib_texture_lookup. Hair doesn't work.