When i render the shadows on to a plane with basic surface they look great, and quality improves with the area samples setting of the environment light.

However when rendering to a shadow matte SHOP surface, the shadows are terrible, and I can't improve them at all, either in the light or the Mantra ROP.

Any ideas what I might be missing?

In your regular beauty render, added an “Extra Image Plane” for “direct_shadow”. This will provide you a shadow matte on the fly.

And I don't know why the ShadowMatte shader looks bad

Hi Jason

I wont take up more of your weekend to explain what I was doing wrong; suffice to say I now have lovely shadows - and learnt a thing or two about compositing and mantra rendering in the process.

thanks!
Mark

Share your discovery would be nice

sure. i was doing it the ‘old’ way, with my background geometry (i.e. plane) having a shadow matte shader. I then went to composite my foreground objects over that. (PBR + the shadow matte shader rendered as poor quality - not sure why - but after Jason's post I realised I was on the wrong track so I didn't pursue it further.)

Instead, for both the beauty and shadow passes, I use the full scene geometry with the normal shaders – except in the beauty pass, the background geometry is set to Phantom (so it is included in reflections and light bounces, but not visible in the output).

Then, as Jason suggested, the shadow matte can be obtained with deep raster (extra image plane) from the shadow pass output.

In COPS, I first composite my beauty pass with the background image (over), then composite the result of that with the shadow pass (multiply).

not sure if this is ‘correct’, but I am happy with the results

P.S. use takes to setup the different passes.