population madness

[digitalguru]

What really helps is to render a separate vegetation pass and adding it with negative multiply in Photoshop.
I did this in some of my renderings, where I ran into the same problem...

I'm planning to do something like that but in Nuke. I'll probably render the foreground flora in Maya and the background in TG. I'll also render out shadows from the Maya flora to comp over the TG terrain so I'll have more control.

[digitalguru]

Didn't see those images when I first refreshed, but very nice! Though my camera is very close to ground level so it's a whole diffrerent raft of issues... 

[Matt]

My 2 cents: If the shadow darkness is a persistent issue, even with path tracers, then the problem lies in one of the following places:

 - The albedo and/or translucency settings of the leaves (including the brightness of the textures).
 - The level of skylight (atmospheric conditions) or other sources of light in the scene
 - An expectation of the light levels and camera exposure that's inconsistent with the render settings.

Reducing leaf opacity to 50% is not realistic, because opacity represents how much direct light is blocked by the leaves, which is usually close to 100%. Scattered, bounced and diffused light through the leaves should be accounted for by reflection and translucency if a path tracer is working well, whether that is Terragen, Arnold, V-Ray, or anything else.

For every photo that has lighter coloured shadows we can also find examples of very dark shadows. It depends on the atmosphere, exposure, surroundings and so on.

If photorealism is important, these are the things I would consider. If not, feel free to use whatever techniques work for you.

[Dune]

Thnks for your input. I know it's not realistic, but it's an easy workaround. Sometimes you don't want more, or any, clouds to have more scattered light, if you increase exposure clouds or whitish objects are sometimes blown up, and if you still want lighter, softer shadow areas, opacity works.
What also helps is using (render) tonemap settings: soft clip effect, contrast.

Intriguing location , btw. I hope you settled in well.

[digitalguru]

I take Matt's point about the object opacity and it is a cheat (but all c.g. is a "cheat" really).

Here's some frames from a video I shot in Richmond recently, the the area in the first is quite open and light bounces around as you'd expect. The second frame is under a fairly dense canopy of trees and the ground is getting bounced light from the environment, but also a fair bit of diffused light transmitting through the leaves I'd say.

Here's a few examples from the net to illustrate:



Translucency doesn't help, no matter how translucent a shader is, its shadows are always black. This is the same in Maya, and the only way I've found so far is to pass a shader with colored transparency to shadows only is with a ray switch.

Dune's solution is the best so far, though lacks some physical plausibility, even when path tracing is on. Must admit I haven't played with path tracing much at all, but it seems not to help in this situation (though I may be missing something).

Next thing I'll try in Maya is adding a little contribution form a second dome light including on the ground, but exuding shadow casting from the trees. Actually light inclusions/exclusions might a good feature to add in Terragen (feature for Terragen 5 perhaps?)

[Matt]

I think the key here is exposure.

In these photos the contrast between sunlight and shadow is as high as what you're trying to avoid, in my opinion. Look how overexposed the sunlight is in some places (outside of penumbra). Why is this accepted in a photo but deemed unrealistic in a render?

[Matt]

Thanks Dune. I am settled in well. Mammoth is an awesome place!

[Matt]

I want to solve this too. I hope I don't sound unreasonably argumentative 😬 But I think at least half the problem is exposure, before we look at what else could be done.

[digitalguru]

I want to solve this too. I hope I don't sound unreasonably argumentative 😬 But I think at least half the problem is exposure, before we look at what else could be done.

NP Matt, it's a tricky one to light for sure, and as you say exposure is key, though I think some "cheating" might be the key i.e light/exclusions for the different elements. moving all the populations to Maya for that reason. My main point is that shadows don't respect translucency (or SSS in Maya) and it's half the battle, but I'll figure something out

[Matt]

Light from leaf SSS/translucency will land on the ground with path tracing (std render/GI cache too, but not very well). I don't think we're missing any major terms here - it's different from the coloured glass transparency issue. But the leaf shaders need to be bright enough in diffuse colour and translucency to make this a strong effect.

[digitalguru]

I tried that with path tracing, but it didn't work, what am I missing?

[Matt]

I think this is a very different kind of scene. The ground would need to be mostly in shadow and surrounded by leaves, like in the photos you posted. I will set up an example and show you what I mean.

[Matt]

Sorry it's an ugly test, and not with real leaves. But this shows that if most of the environment is a green canopy then the ground picks up the green. I increased exposure slightly, but only to a value of 2. Your photos have much higher exposure where the sunlight is overexposed. I could have done that here and it would have made the shadows even lighter.

Your test renders on page 1 are mostly lit by the open sky, so the shadows won't look much different from the default scene. If you put yourself in the position of a pixel on the ground, and look at what's all around you, that gives you some idea of what colour the shadows will be. If it's mostly sky, the shadows will still be dark blue. Compare this with the photos you posted. In the photos the ground is mostly in shadow (at least 50%), surrounded by green leaves. There's one exception where the shadows are blue, but in that photo the exposure is very high. Where the sunlight hits the ground it is *very* bright, which means the exposure was increased considerably.

[Matt]

(Bad quality screenshot because I'm going through remote desktop)

If you boost your leaf shaders to these settings and surround the area with trees I think you'll be able to get plenty of green light on the ground. But the texture maps will have a darkening effect, so be careful with those. I increased the PT quality to 64 but this is just a quality/AA trade-off, and I don't think it's necessary for the effect. Not shown: Camera exposure = 2. This alone is enough to brighten the shadows quite a lot.

[Matt]

To give some perspective: as we move away from the trees, the shadows return to the colour of the sky. This is because it's not the leaf opacity that allows the extra light on the ground, it's the light scattered down from many directions.