CGTalk - 8.5 hours for highres FG /GI render... can it be shortened?

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stormfrog

01-19-2008, 04:53 PM

Hi!

I am playing around with MR and learning different lighting models proved to be alot more advanced than I had any idea it would be. Modeling seems trivial compared to setting up lighting now.

In my latest learning session Ive been exploring FG and GI using only "bounce back" lighting. (That is light source aimed at reflectors that the reflector or "barndoor" reflect back at the object and where the lighting is controlled by adjusting the color/irradiance of the reflectors materials. Much like what is used in Photostudios, I am sure all of you already now of all this I am just describing it since I dont know what this "light model" is called.)

Anyway, in my latest render I wanted to leave the safety of rendering my boxes and spheres and try and use this light setup to imitate a photostudio scenario with real lighting using reflectors, barndoors and most important - a pretty model in the center of it all. I used "Victora 4" mesh from DAZ Studio for that purpose.

When I cranked the settings up a bit I found that the rendertime became overly long. I am wondering if anyone here have any experience with optimizing a scene using FG/GI that would help me bring render times down.

The scene consist of a high poly mesh,
All textures is 30Mb (about 20 different files, where most are 2500x2500), but they need to be huge to produce anything good sine I want to render a HighRes image equal to a photograph.
FG is set to 500.
GI Accuracy is also set to 500.
Using two Maya Area lights (old style converted from Spot Lights, I hear MR has native lights for that now) with its detail set to 6 x 6.
Render size is 2400x3200
This took 8.5 Hours to render :P

Image:
http://www.acc.umu.se/%7Estorm/misc/share/cowgirl_render-finalgather-globalillumination-lowres.png

-> HIGHRES (http://www.acc.umu.se/%7Estorm/misc/share/cowgirl_render-finalgather-globalillumination-hires.png) <-

Also, the high resolution didnt turn out very impressive at all. It is nothing like the detail you get with a photo, I suppose I would need even larger textures to get it right? :P

master-soldier

01-21-2008, 06:29 AM

What kind of hardware are you running?

Hejl

01-21-2008, 08:17 AM

Hi, did you try lowering contrast treshhold to say 0.02?
Cheers

HellstormDe

01-21-2008, 12:41 PM

Hmmz0r... I don't really like FG. Results from GlobIllum are ways nicer and faster. IMHO FG is still only useful in combination with GlobIllum. This way you also don't need such high FG settings.
I still consider FG as a final touchup of a Global Illumination pass.
Maybe that way you even don't need an accuracy of 100.

If you are still missing some detail shadows, try to achieve them with Ambient Occlusion.
This way everything should be much faster.

Ash-Man

01-21-2008, 07:00 PM

Maybe the time was gone calculating the bounce on her large boobs:)

Dude you defiantly don’t need this huge texture file ……rule of thumb..textures size is about 1/3 of the final rendered image

So the textures can be done with 800*800 easily.
It’s just a simple waist of your render time with no noticeable result.

As for rendering for print
Look for a thread by Master Zap

He talks about what is a proper DPI and rendering for print

mehran

01-27-2008, 03:59 PM

I herd textures had to be double the size fo the rendered image, so as to compensate for zooming in and stuff..
...
anyway
....
your Fg settings are on steroids...:Literally ... try 50 rays with hundered accuracy and you 'll get the same result..
and as mentioned before the cotrast settings don't need to be at 0.1 when you go up the rez size..it needs go down.
One last thing, you right now are not using any fancy (hard to render shaders) and trust me if you were to give here some shinny bra with blurry reflection.. your render time will rocket to 2 days or something equally insane..
Cheers and keep researching ...
(a good method for rendering hi rez himages is to break them up into tiles)

stormfrog

01-30-2008, 10:57 PM

Thanks for replies everyone.

I had no idea FG setting could be as low as you describe, some tutorials Ive followed often stated that a level of 500 is good but preferably higher setting should be used for finetrace.

Ive never used GI in itself w/o FG to complement it. Mosty because I dont really understand how GI works I suppose. Usualy my GI scenes get dark blotches or just to bright and it seems to take forever to tweak the GI settings for the scene.

As for texture size, my "work size" when I was working with the scene in maya textures were down at 512x512 to make hardware texturing possible. But the test renders aI did with that resolution turned out very poor when you zoomed in on details of the model. I suppose for a "shot" like this textures of lower resolution should have been used. Then I could copy back the highres textures for closeup renders of eyes/face etc.

And btw, Im running a medicore intel 2.8 32-bit cpu and 2Gb ram. Its nothing fancy, but it usually get things done reasonably fast. Then again, Ive never rendered anything quite this large wiht these settings before.

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