I have a fundamental question here, and I'm really hoping there's something I'm missing that you fine folk can help me with. I'm having trouble with ambient lighting in areas with PBR. Essentially I can not figure out any way to use an ambient light (does not seem to connect with PBR) or a way to increase the intensity of indirect lighting (bounces)

I've attached a very exciting pink donut wedged render comparing PBR and a secret no name brand render. Excluding the name as it's not about the other renderer, it's about the look and getting it going in Houdini.

Going from left to right, we can get similar looks going from 1 Diffuse Limit (bounce) to 3. I Struggle finding a way to raise the dark contact points, to bring up some of that detail. This is not the same as just lifting the bottom end in comp, I want to actually see more detail exposed.

Thoughts?

- Phunt

Hi,
not sure what your or the unknown render's definition of ambient light is, but ambient lighting is an old school trick to use instead of doing a form of global illumination by simple adding some light wherever and really doesnt belong in the world of physically based rendering. The ambient light was invented to compensate for the lack of indirect diffuse illumination.

A dirty hack for times when you still had to sell your wife, kids, car and house to buy a SGI if you wanted to rock and roll to the tune of 25Mhz of pure power. :p

Ambient lighting can be applied locally with many lights to fake GI but that is the kind of work you save youself from doing when doing physically based rendering at the expense of rendering time.

So I think PBR ignoring ambient lights is quite correct. Just up the env light or add other lights and increase diffuse bounces. Think like a photographer. Need more light? Add bounce cards, set up a light, etc.

And when rendering the thing in floating format then changing the exposure will bring out more detail in the shadow areas. Again just like the real world, need more light in the shadows?, expose longer or light more.

</rant>

-Fabian

So I think PBR ignoring ambient lights is quite correct. Just up the env light or add other lights and increase diffuse bounces. Think like a photographer. Need more light? Add bounce cards, set up a light, etc.

And when rendering the thing in floating format then changing the exposure will bring out more detail in the shadow areas. Again just like the real world, need more light in the shadows?, expose longer or light more.

I think the problem, in a production environment when you have let's say 400 talking animals to light and the inside of the mouth is too dark, is that it's pretty fiddly to start putting bounce cards inside mouths, extra lights, etc. We need to be able to access physically bogus hacks, and do it easily.

Fabian
Hi,
not sure what your or the unknown render's definition of ambient light is, but ambient lighting is an old school trick to use instead of doing a form of global illumination by simple adding some light wherever and really doesnt belong in the world of physically based rendering. The ambient light was invented to compensate for the lack of indirect diffuse illumination.

Heya!

Right you are. In the end I need a way to control these low level values to pump some lighting information in there. You're right of course about what an ambient light traditional does, but some engines will contribute the ambient light to the actual irradiance solve. So it doesn't just lift the blacks like a curve would in comp (traditional ambient light) but instead actually contributes information revealing more detail in your render.

Ambient lighting can be applied locally with many lights to fake GI but that is the kind of work you save youself from doing when doing physically based rendering at the expense of rendering time.

Yes and no. On something really simple like this, sure. But think of an armpit or something like that, maybe not. An organic shaped nook that's constantly moving, and the needs of how much light you'd need to apply to balance it out also constantly change. It's just a case of control. Yes there are ways to do it manually but if you have hundreds of shots you want to find a way of making this process and procedural as possible so you can concentrate on cool things like lens flares and lasers. Well maybe not lens flares and lasers, but you you get the idea

Think like a photographer. Need more light? Add bounce cards, set up a light, etc.

Yes and no imho. The thing about lighting in a purely physically based way, is assuming your lighting render engine is 100% perfect, you'd now need to have every shader acting real, and everything modeled even off camera, every minute detail to interact “physically based.” Comes down to I want to be god in my cg world and follow or break the rules whenever they are convenient to me to get the results I want

For some reason I always want a pink donut.

- Phunt

Yeah I totally agree of course with the need for local fixes and control, just not ambient light being the solution to that. For example with 400 characters I would not want to lift the light levels in a whole scene and every shadow to light up the mouths a bit. That's what global ambient does, in the lighting arsenal it is about as indescriminate as a nuclear weapons or anthrax.

So you either end up with some sort of localized hack, be that a small point light you constrain to your characters armpit hair (ewwwww) or you render out masks/normals/position/etc channels and take those tweaks in comp. Personally I think that tweaks like that belong in comp or shaders.

In the render you light so that the F-stop (yeah that doesnt translate well i know) range isnt totally out of control. You can always control your black and white levels in comp. The nice thing in 3d compared to the real world is that you can simply go ahead and turn down the intensity of the sun to you hearts content or add as many 16k HMI's as you please for free

If you haven't already, have a look at some of the tools Image Engine had for district 9, http://thefoundry.co.uk [thefoundry.co.uk] (link to video a bit down on the page) really nice control for tweaking lighting and all in minute detail. Nuke really looks fantastic for that sort of stuff.

Just some thoughts to be taken with as much salt as you please We all have different problems to solve and different ways of doing so.

Best regards,
Fabian

One more thing, you are looking at your render region/mplay with gamma 2.2 right? Default is 1 for some reason which is beyond me.
-Fabian

What Fabian said in his last post. Make sure you're viewing and saving gamma-corrected images, linear workflow and all that. Then you should see more light in your nooks and crannies. I can't be 100% sure but it doesn't seem to be the case in your mantra renders.

Personally I think that tweaks like that belong in comp or shaders.

I tend to agree with this. :]
If you really want a particular object or objects to spit out more light than what the scene is contributing you could also increase the albedo in your PBR shaders.

Hey guys,

Thanks for your 2 cents. It's not a lin vs SRGB workflow issue. As even if I was crushing the black point with a bad LUT or what have you, I'd still like to have the control to push the low level values wherever I want.

I was hoping there would be some controls in the ROP that I had not taken advantage of, but seems there is not the case. SESI also mentioned exposing albedo controls on the SHOP level, so seems like that's the best bet at the moment.

Off to play in shaderland I go!

- Phunt