"Ambient" shadows

Started by bigben, September 10, 2007, 01:35:41 AM

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Here's something to try now that the bug fix for populations is released.... Add a light with an elevation of 90°, Strength ~0.5, soft shadow width ~45°. Use it with a fill light setup of GI. This should put some subtle shadows under trees that should greatly enhance the realism. (Settings from a quick and dirty trial, so they may need some refining)

The test image isn't the greatest, as settings were chosen to accentuate the difference between the sun's shadow and the ambient shadow (12 samples used, detail 1, aa 4).

I'll post something better after I run some more population tests.


Hi Ben,

What was your 'soft shadow diameter' setting in this set-up?

Volker Harun

Nice gradient shadow. Like it.


Quote from: choronr on September 10, 2007, 02:27:29 AM
Hi Ben,

What was your 'soft shadow diameter' setting in this set-up?

Quote from: bigben on September 10, 2007, 01:35:41 AM
Add a light with an elevation of 90°, Strength ~0.5, soft shadow width ~45°.  ...12 samples

Shadow from sun using default soft shadow settings.

The original strength of my zenith light casting a shadow in my fill light shadow was 0.15, but the increased diameter reduces the intensity of the shadow


I've come back to this as part of my fill light setup review... but I'll leave that part of it out for now as this works with or without GI. Have a look at the shadow of the tree cast by the sun in the attached image. You'll notice that it is darker under the canopy of the tree, than out in the open.   Now get your nose off the monitor, give it a wipe (the monitor ;)) and lean back. Now you should be able to see a faint shadow under the canopy of the tree as well.

Setting this up with a single light is quite tricky as it's a big balancing act between getting a dark enough shadow and overpowering the sunlit areas with the extra light. The wider you make the soft shadow, the stronger the light has to be to be able to see the shadow... and the worse it makes the rest of your image look.

This is where I borrowed some stuff from my fill light setup (with a slight twist) to simplify the process. Taking the available properties of lights inTG2 into consideration we can split this dilemna into separate components and solve it with only two lights.

1. For sunlit areas we don't want any additional light (with GI on) or only a small amount of light (with a fill light setup) - Duplicate the light and stick a minus sign in front of the intensity.

2. But this will remove the shadow as well - turn all shadows off on the duplicate light

3. I want the shadow to have a different colour - choose a colour and look its HSB value (Hue, Saturation, Brightness).  Invert the Hue value only (for windows, add or subtract 120... whichever gives you a positive number < 240) ... apply the colour to BOTH lights. (Try the red decay colour)

4. (For fill light setups) I want to add a slight colour to all light from above that is different to sunlight AND have a complementary colour in the shadow under the tree - increase the intensity of the duplicate light slightly (duplicate light doesn't completely cancel the soft shadow light)

This provides you with separate control over softness, intensity and colour of the shadow with a minimum of variables. Dead simple and easy to control.

The soft shadow in this example is only 30 degrees.... should have made it more like 60

To use this as an example of how the control is simpler.....
The intensities of the 2 lights in this example are 1 and -0.7 
In areas under open sky but shaded from the sun the total effect is that of a warm light with an intensity of 0.3.
Areas shaded frm both the sky and the sun are darkened by 0.3, and have a sky blue cast.

Now I've increased the soft shadow diameter to 60, which will make the shadow much lighter.
Increasing the intensity of the shadowed light to 1.5 gives me a shadow with the darkness I want, and to restore the colour balances I had, the difference in intensities needs to be 0.3 ... i.e. the second light now has an intensity of -1.2 (inset in attached image)

The shadows have been tweaked while retaining the rest of the lighting completely intact without guesswork :)  Shadows near the trunk are now slightly darker, while shadows at the edge of the canopy are roughly the same.

I still have some more work to do on my fill light setup before I post the updated version. I'm not entirely convinced by my colour selections yet....


At the risk of starting another monologue   ;)

Here's another test with a lighter background surface (A side note that the fake grass I set up using fake stones requires a render detail of 1 to work ;) Detail dropped to 0.5 for this test to cut render time down)

The main image uses the same settings as the previous post and you can see that the colour is definitely overkill.  The shadows a bit strong still but I may have to check at the higher detail level as extra softening may lighten it.  The excessive colour cast does however illustrate a possible hack for tinting surfaces under tree populations without having to figure out where the treess are. A typical situation here for example would be paddocks with dry grass and bare brown soil below the canopy from animals seeking shelter from the sun. While not entirely accurate, a brown shadow under trees would look effective from a medium distance... IIf only you could feed shadows into a surface mask.....

The inset is the same colour with the saturation dropped to 20 (8%) confirming that the colour was largely due to the overhead light and not the other blue fill lights.

@nvseal: The clouds are your clip minus two cumulus layers picked at random (4 & 5) Thought you'd like to know so you can see what they look like from "a little" lower.  I'll have to run a render of each layer individually to see how they look from ground level so I know which ones are which. It's going to be awfully tempting to include them in a version of this animation project, even if just to see how the clouds scale on the way down, and watching them morph as their fractals are animated.


"His blood-terragen level is 99.99%...he is definitely drunk on Terragen!"


Hi Ben,

Thank you for all this good information. I was hoping more of those out there would be gleaning this info. I would like to see you posting more in the various galleries. With your knowledge of TG2, I would expect to see some of your knowledge applied; and, masterpieces they would be!!


Quote from: choronr on November 04, 2007, 09:19:58 PM
With your knowledge of TG2, I would expect to see some of your knowledge applied; and, masterpieces they would be!!

I'm actually a bit light on for masterpieces... having too much fun tinkering and keeping the brain active. I'm enjoying this NZ terrain at the moment so I should put at least one proper render together soon  ;)   I'll probably have something put together by the time I finish working through Volker's tutorial.


Quote from: bigben on November 04, 2007, 09:58:04 PM
I'll probably have something put together by the time I finish working through Volker's tutorial.

That I am really looking forward too :P
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Ben, thank you for all your excellent input helping us with your good ideas ...they work!! I look forward to seeing your creations in the galleries.