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Hey BSE, thanks for reading!

I'm working on a project in which my scene is brightly lit solely by world surface emission. This creates a stark, bright "ambient light" or "global illumination" look, with subtle shadowing in corners and tight spaces.

This was exactly what I was asked to achieve and everyone's happy - until the project lead asked for interesting shadows.

My task now is to:
1. somehow introduce shadows that can be cast by a lamp in a normal, intuitive way.
2. force those newly-shadowed areas to be darker than they should be given the ambient light.
3. ideally, prevent those lamps from adding any light to hit surfaces.

The problem is two-fold:
1. The lamp which casts these shadows should not necessarily add light to the objects it hits.
2. The shadows cast must be much darker than the ambient temperature of the shadowed surfaces.

I'm convinced there is a clever way to achieve this in the compositor, but I'll be darned if I can figure it out.

Can someone help me learn to achieve this illusion? A push in the right direction might go a long way.
My humble thanks,

Edit: Added Screenshot: https://i.stack.imgur.com/7uGar.jpg

Screenshot

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  • $\begingroup$ Did you already considerd using different render layers and compositing (I saw the tag)? Would they be suitable for your project or you need a on-the-fly solution? $\endgroup$
    – Carlo
    Jun 17, 2016 at 19:56
  • $\begingroup$ I'm entirely open to using render layers - I'm posting because I don't know the procedure required to achieve this particular effect. A standard "shadow catcher" setup was interpreting anything NOT illuminated in green (in the above exampe) as a shadow, whereas I need to isolate and manipulate only the shadow cast by the lamp. $\endgroup$
    – AlwaysSunny
    Jun 17, 2016 at 20:10

2 Answers 2

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Use two different render layers

Put the "lamp" on a separate layer and Exclude that layer from the render by clicking on the corrisponent box in the Layer panel.

Your scene now should be affected only by the environment's light (and eventually other light sources, but not the mentioned "lamp").

enter image description here

In the second render layer, uncheck the Use Environment box to remove world's shader influence. The result is a scene lit by the lamp only. Enable this this time the Shadow pass in order to acquire the info about where the shadow fall.

enter image description here

Finish by color mixing the Composite pass from the first render layer with the Shadow pass from the second with Multiply option. Use the Factor slider to adjust the influence of the lamp's shadow in the final image

enter image description here

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    $\begingroup$ Ah, this is excellent! Not nearly as complicated as I thought. I somehow completely missed "Use Environment" - having never clicked on it before. That was the key. I also needed to involve (render, film, transparent) and a third render layer to get rid of the black world (which was visible to the shadow layer frustum) and superimpose these results atop the original world color. Now I have exactly what I wanted. This is a top notch solution. My sincere and emphatic thanks, kind stranger! $\endgroup$
    – AlwaysSunny
    Jun 17, 2016 at 21:21
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Would using a Cyles Ambient Occlusion be an option for you?

It is basically unaffected by lighting and ignores any lamps you add to your scene but generates this sort of proximate global illumination that your described in your question by itself.

If combine with a diffuse shader and you can get some sort of direct control over the intensity of the shadows/light influence. It will still react to the sun light, but it's effect will be less visible.

Ambient Occlusion

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  • $\begingroup$ This looks like a novel effect - I've never seen the AO node used before, so this is new to me. However, I'm pretty sure this will not contribute towards the desired outcome. I added a screenshot to my question which showcases the issue / desire. $\endgroup$
    – AlwaysSunny
    Jun 17, 2016 at 18:48
  • $\begingroup$ Are you willing to make a switch from Rendering engines at this point in work? You could easily achieve the illustrated type of effect using Blender Internal and a "Shadow Only" type of lamp, this is not very suited for a physically accurate type of engine like Cycles. $\endgroup$
    – Duarte Farrajota Ramos ♦
    Jun 17, 2016 at 19:07
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    $\begingroup$ Aww man, that sounds tempting. I'm hopelessly in love with Cycles though. Maybe there's a compositing technique that could use both engines, though I seem to recall that's a huge pain to do. $\endgroup$
    – AlwaysSunny
    Jun 17, 2016 at 20:12

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