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enter image description here Using the standard layers / compositor setup created with the Setup Tracking Scene button (in Cycles), I've used the second layer 'Background' to build a rough mockup of the street in order to act as a shadow catcher. However:

1) The shadow-pass for this layer is always entirely black. Is that correct? If not, how do I correct it?

2) With default settings, the shadowcatcher model darkens EVERYTHING it covers in the render, whether a shadow is cast there or not. I imagined that shadowcatcher layers should ONLY darken the movieclip in areas where the foreground layer (the ship model (please ignore the cube!)) is casting a shadow - that's not happening... so how can I achieve that effect?

3) Is bothering with Ambient Occlusion more trouble than it's worth for the shadowcatcher model? Given that the ship rarely touches the roofs, etc, but that the shadowcatcher model has lots of places with planes meet each other, etc...

(Still quite new to this! Please explain like I'm five!)

All the best,

--RoB

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    $\begingroup$ In my experience, you should get rid of the entire starting compositor node setup...it's designed for BI, not Cycles, and things like Vector-based motion blur and AO effects can be done in Cycles without any need for the compositor at all (sampled motion blur is better than vector-based, for realism at least, and since Cycles has true global illumination AO is really just redundant). And, even with those things aside, the default node setup just didn't...work for me. The results looked nothing like what it should have $\endgroup$
    – markasoftware
    Commented Oct 20, 2015 at 0:54
  • $\begingroup$ Those are interesting points and they definitely point the way for experimentation in future. However, at the moment, I just want to get shadow catchers working with cycles. If you can suggest a compositor node setup that'll work for this as opposed to the default, I'd appreciate it! $\endgroup$
    – Reverend Speed
    Commented Oct 20, 2015 at 15:10

3 Answers 3

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As Sanix, Marasoftware and Sebastian Kónig point out (https://twitter.com/s_koenig/status/656693360955150336), the Cycles shadow pass does not work with environment texture lighting (nor does it work with mesh lighting), hence my shadow pass was entirely black.

A number of solutions were suggested, usually to identify the direction of the environment texture sun light ("Is there anyway to match a sun lamp to the direction of the sun in an environment map?") and then to mimic this light with a sun lamp, excluding it from the main layer. This made a lot of sense - and then I happened across the following:

Cycles: Shadeless "Shadow-catcher" Material for Rendering onto Footage

What a brilliant, simple idea! Render the shadow catcher twice, once with shadows from your main object and once without - then subtract the clean shadowcatcher from the shadowed layer, leaving only the shadow behind! (Then use RBG curves or what have you to tweak the darkness of the shadow).

Barring any future mishaps or objections from the community, I'll be using this in from now on.

Two side notes:

1) This seems like an insanely useful material for this kind of task in future, though I haven't done all my research on it yet. Could be handy for someone doing a little compositing...

2) Had some trouble with backfaces in my Cycles shadowcaster, this solved my problem. Hope it's of use.

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I can't see your whole scene to make sure of this, but the first thing that comes to mind is that your lighting setup isn't done properly. I can see from the top bar that you do have one lamp, but I'm guessing that's just the default one, which doesn't do very much. To test if this is the case, just create a sun lamp and point it straight down, which should get rid of most of the shadows. I've found that using anything but sun lamps often becomes an issue with motion tracking, so before you go into more advanced lighting just put in a sun lamp to make sure that lighting really is the fix for this

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  • $\begingroup$ Lighting for the scene is derived from a single environment texture (non-hdri .jpg equirectangular) created with Photosynth. This is the same process used by Corridor Digital and Freddy Wong ( youtube.com/watch?v=m4OvaVXEzgA ) and seems to light the scene effectively, despite my ongoing problems with the shadow catcher. I'll look into the sun lamp now! =) Also have further experiments in the works... $\endgroup$
    – Reverend Speed
    Commented Oct 20, 2015 at 15:15
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    $\begingroup$ So! The shadow path definitely needs a lamp of some kind - it appears to be mostly working now! The issue is trying to get the light to match up with the environmental texture lighting... $\endgroup$
    – Reverend Speed
    Commented Oct 20, 2015 at 15:22
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Did you add light sources? I get the same effect when I try to render an object without first adding light sources. If you do have light sources, make sure they are positioned correctly.

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  • $\begingroup$ Thank you Sanix25! Please see my response to Markasoftware above. $\endgroup$
    – Reverend Speed
    Commented Oct 20, 2015 at 15:15

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