need help lighting scene using portal lights + Phy-Sky

[copain]

hey steve

Have you looked into using a custom light rigg (faking GI)?
I do not do that many animation stuff, but I think that would be a better option for you.

[mister3d]

If we didn't have problems with sampling, we would just turn on outdoor lighting and light would come through windows in our scenes. But unfortunately light has a finite quality, so we must use it more economically. Usually you set your area lights in window frames, not behind it. You need your light only going from the area of your window. Create area lights just to fit into window frames and exclude the glass from it not to bother with refraction.

When it comes to animation, the best option for you is to fake GI. First of all setup your lighting in usual way, place your lights where you want them to be for GI setup. Make test frames with GI. Save them for reference. Now turn off Gi. Copy your area lights and place them behind each wall, floor and ceiling. Also under the surface of the table and exclude each surface from corresponding light, meaning if you place a light under floor, it will mimc Gi from the floor, but you want it be under it, not above, so you need to exclude the floor from this light. THe intensity of 2 window area lights was 10, when each fake Gi light had from 0.1 to 0.3. You don't nessesarily must be presice in mimcing your GI, use your own judgement what looks good.
I setup basic fake Gi, but some small areas still were too dark, so I placed spotlights and included into lighting only the objects I needed to brighten. I also linked 2 lights to the character as he will move during the animation.

http://img249.imageshack.us/img249/4161/rendertestsku9.th.jpg (http://img249.imageshack.us/my.php?image=rendertestsku9.jpg)

http://img249.imageshack.us/img249/9933/setupshememy8.th.jpg (http://img249.imageshack.us/my.php?image=setupshememy8.jpg)

It took me 20 minutes to setup. Now I can render flicker-free animation for 4 minutes a frame (765x576 on one quad-core), which is not incredibly fast of course, and I'm sure if I used not area lights for fake GI lights but spotlights with depthmaps, I would win some more time. I didn't do tests yet but it's certanly faster.

...Ok, I made a test with spotlights with depthmaps instead of area lights with raytraced shadows for fake GI lights, leaving window lights area lights with raytraced shadows. I managed to cut rendertime in half, which is now appr.2 minutes vs 4. All you need to care is the resolution of depthmaps(called shadowmaps in 3ds max) and its blur. Try to set low resolution and then blur it to get rid of concrete shadows from them.

Your grain is from low sampling quality either in your area lights, or in global sampler. Also when you set your area lights exactly into window frame samples will be used more economically and grain will decrease. But this grain is nothing in comparison with Gi noise. That's why I suggest to using fake GI. It's very hard to setup fast and flicker-free Gi, especially in mental ray.

http://img216.imageshack.us/img216/7052/depthmapsci0.jpg (http://imageshack.us)
http://img216.imageshack.us/img216/depthmapsci0.jpg/1/w712.png (http://g.imageshack.us/img216/depthmapsci0.jpg/1/)

[SteveN25]

Wow thanks mister3d. Im trying this just now, sorry been busy sorting out my xmas shopping, now thats outa the way I'll get back on to this.

This all makes sense but the one part im struggling with is this bit

"exclude each surface from corresponding light"

I know what you mean but Im not sure how I actually do this.Do I need to split the model into pieces and change each surfaces renderstats or is it something to do with light linking.

Im using maya so if you could explain how to actually exclude the lighting from certain surfaces that would be super.

I very much appreciate your help.

thanks
steve

[mister3d]

I know what you mean but Im not sure how I actually do this.Do I need to split the model into pieces and change each surfaces renderstats or is it something to do with light linking.

Im using maya so if you could explain how to actually exclude the lighting from certain surfaces that would be super.

I very much appreciate your help.

thanks
steve

Yes, you will need to split the walls into 4 different walls and separate ceiling and floor. Also main surfaces affecting your lightiing will need fake Gi light too, like the table surface. This is because you need each your light to represent the bounce light from each wall, ceiling and floor. But you need the wall not to cast shadows and not to being lit by this light from back. So you exclude the corresponding wall from lighting, illuminating the rest.
About how you include or exclude one object from lighting in maya I don't know, try to search in help files "light linking", or "selective lighting", "lighting exclusion" etc. It must be in your light source options.
I made an animation with depth maps and I can see some flickering on the main character. It must be low settings of depthmaps causing this. I will need to test this further. You can of course use just area lights with raytraced shadows, but it will be longer a bit.

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