How would you approach lighting this scene for quick render?

#1

http://spittle.cgsociety.org/gallery/872677/
edit - the above image no longer used as example - see below for new example***

Anyone fancy mentoring me with rendering this scene?

This still shot at 800x600pix renders in whopping 45 minutes using an Intel core2 duo 2.4GHz processor. I was also writing a word document whilst viewing a pdf during render.

I’m using mental ray, AA=1,16 using Mitchell filter.

I’m using final gathering on low. 1 bounce. Mostly MR Arch & Des materials, a couple of standard ones too.

The scene has about 300,000 polys, lit by 8 photometric lights using ray tracing, also a spot light again using ray tracing.

I have a skylight in my scene.

[actually the image shown was rendered on diff PC with similar settings. Don’t have info so checked render time on my home PC - but the one I just rendered has an additional spotlight so the scene has some exterior lighting too, the skylight also contains a gradient ramp, also used in environment slot].

This is fine for still shots however if producing an animation of the sequence of construction for example, with the crane positioning the pumps, say five or 10 minutes long, then I’d need a serious rethink in my approach. Low final gather would also probably flicker a lot.

I understand some of the components, ray trace shadows, mitchell filter etc impact on the render time however I’ve yet to be successful with any work arounds whilst keeping the same render quality. My fake GI’s show multiple shadows so I’ve always reverted back to longer render times.

So how would you do it? Would you fake GI -how? Use shadow maps for shadows? Buy a new PC?! I have a faster one at work but again animations still would still take a long time to render using the methods I have been.

edit If I delete all lighting, and revert to default lighting, no FG etc, and render at 720x486, the render time is reduced to 3mins 40sec.

#2

Hi,

Since you’re using mental ray consider deleting your lights, adding a daylight system and place MR Sky Portals in the windows. It seems to me that you’re overcomplicating things.

Also, a great tip, use an override material (there is a slot on the rendering dialog under ‘processing’), just a mid grey coloured MR A&D material with no reflection to make your scene a ‘grey card’ while you’re setting up the lighting and when you’re happy with it, turn of the override and start working the materials.

Check the help for setting up a daylight system with a MR exposure control and a MR Sky.

J.

#3

On top of J-man’s advice, have you ran a test with the AA dropped to 1:4? also switch to BSP2 (default is BSP)

You wern’t too clear on whether or not you’re using GI.

45min sounds waaay too long for a scene like this.

#4

Daylight system only won’t cut it. It needs to be well illuminated hence the interior lights. I originally used a daylight system with MR sky portals placed in front of the windows and doors but I couldn’t work out how to expose the interior without blowing out the highlights created by the sun.

Even tried exporting a HDRI to try and tone map it but only have Gimp at work and not photoshop.

I’m just using FG.

I’d like to keep the scene at 1,16 AA minimum as sometimes there will be smaller pipes than on this image.

I’ll try BSP2 also.

This project is done and dusted by the way - I’m using this scene though to try and improve my skills.

Thanks for the replies.

#5

Actually, I have a feeling my scene has something funny going on. The version I have at home was originally crashing every time I rendered, I fixed that but it does seem a rediculous render time. I orig thought it may be due to my home PC only being 2x2.4GHz however since working on another scene I think perhaps scrap this idea.

Can you offer advice on this scene instead - again just an example.

Now this scene has the same settings, renders at 1min 54 on 8x2.66GHz. How could I improve this setup to get the render times down to say a minute?

I maybe have a job in the pipeline for an animation for about 10 mins. this is what sparked the trial.

On my home PC this image would still render in about 8 mins resulting in a very long render time at 15000 or so frames.

#6

If I had 15000 frames to render, I would fake the GI by putting spots around my scene with soft shadow. Or maybe no shadow at all and some occlusion on the model. That way you could bring the render time down to under 20sec per frame.

For corporate videos I tend to optimize my scene if renders go over 30sec/frame. You cannot let render time crash your deadline.

By killing GI, you get faster feedback on your scene and can improve your reflections and overall mood way faster.

Or you can bake a GI or occlusion map on your object, then kill the GI and keep the good look.

#7

Any tips on faking GI on this scene? I tried this and I ended up with multiple shadows and it looked crap. I’ve made it work around a simple object before. Is there a methodical approach I can use?

What kind of arrangement would I need?

Baking won’t work because I plan to animate so shadows will be moving - I had thought of this. [saying that I guess I could bake the light into the roof and walls. Not sure that would be worthwhile as can’t bake light into all of the other objects.

Please keep tips coming - much appreciated. I’d love to get this nailed.

#8

On my home PC (2x2.44GHz), using AA1,16, low FG with 1 bounch at 800x600 I get 17mins 9 seconds.

I then used this tutorial to fake GI: http://*******.com/team/Tutorials/fake_gi/fake_01.php

This got render time down to 7mins 34. Interestingly with no fake GI, with no FG or fake GI the render time was slightly higher at 8mins 24sec.

Here’s the faked image. Problems:

-shadows are washed too light, makes image look washed out.
-I’m unsure how to tackle the fact that I have clad walls blocking half of my fake GI lights. The dome of lights is located outside of my building and obviously half of them arn’t going to be doing anything.

#9

what is that " http://*******.com" ???

Sorry, as I am using lightwave most of the time it would be hard for me to tell you more precise info for 3ds max.

Your fake GI image look good none the less. Reduce the numbers of rays bounce for the reflections. Also blurry reflection are crazy long to render. i would try to use a blured reflection map for this. It would be less realistic but the overall feeling will be the same.

#10

Thanks for the tips earwax, I’ll give them a try.

The link was:

3dt0taldotcom/team/Tutorials/fake_gi/fake_01dotphp [just swap the 0 with O]

Is there any particular reason why we can’t share tutorials from this site without them being blocked?

[font=Verdana, Arial, Helvetica, sans-serif]“Fake GI” tutorial [/font]by Bonar Siregar

Do you have any advice regarding the fake GI light dome when there are outer walls and various other objects blocking some of them?

I was wondering whether I need to be doing something a little more complex with the lighting rig as there are so many object. A close up of some areas may bnot be so forgiving.

#11

Considering you intend to animate this scene the first question there are a number of considerations.

  1. Will the scene be “Static” or will objects be moving around? If yes, then you will want a fake GI solution. If no, then you can store your FG one cache file with low or even draft settings then have nodes read from it for flicker free FG.

  2. how close will you get to any given object in the scene? I’m asking because you can get away with shadow maps at a distance to get that softer diffuse light source look without the render time it takes to do it for real with raytraced area lights.

  3. No matter what lighting method you go with you’ll want an AO pass or you can build it into your shaders to save a separate pass but I thing a separate pass is the way to go.

  4. Beware the glossy reflection! If you don’t need the material to really reflect then don’t. Many of the preset mats in MR can eat render time if you don’t tweak them, especially if they have blurry reflections. For example your steel beams would most likely not have any significant reflection in the real world. Use fast interpolation or even FG / highlights only to save on render time.

There many more tips I can think of but it really depends on what approach your taking. Hope that helps a little.

#12

That is helpfull. This scene in particular is low budget, a days work with several design changes along the way hence the materials are just thrown on.

I’d like to be able to use the fake GI technique some decent textures, probably with some maps painted in photoshop or procedurals blended with alphas. And of course some standard Arch & Design materials. I get what you’re saying though about the glossy reflections.

I guess I’d like to understand the best options for both static scenes and where objects are also moving. It’s likely at some point I’ll have to show sequence of construction and it would be nice to show the pipes growing, so would need to save FG atleast every 4 frames. Saying that, I still find you get flickering unless you have resonably high settings and long render times so I’d ideally like to avoid FG and I’d like to get renders super fast.

Any ideas - should I be having multiple lighitng rigs, some excluding certain obejcts? As I said before, the walls on the far side of the render are occluding half of my fake GI lighting rig hence it looks a bit crap.

And are you saying shadow maps are not suitable for close ups?

#13

I’ve started a new thread here that’s a bit more specific to what I’m tring to acheive and in the lighting forum. Please post futher comments here:

http://forums.cgsociety.org/showthread.php?p=6528678#post6528678

#14

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