How to render a shadow pass with GI contribution in an efficient way...sorry again

[olika]

I´m more and more afraid i`m annoying you all with asking the same questions over and over again

It´s not that i`m not able to solve it, but i still feel i`m messing around with it and still not satisfied or sure i understood everything right...
Maybe some of you feel the same, but ok, first things first, already have an old thread here:
http://forums.chaosgroup.com/showthr...w-what-do-tune

Thanks to Morbid Angel who helped me out how to do it correctly:
"To produce a shadow, what you need to do (what I usually do) is turn off gi, so direct lights only, set your shadow casting object to be visible to camera off, set your plane (shadow receiving object) to be vray properties matte, alpha -1, shadow, affect alpha on. "

But still i`m running into some things which rises questions to me, hopefully some of you can put some light on this, see the following renders:


Let`s take the RGB Render as a reference how i want the shadow to look like.
Client wants that render with one layer the object itself masked and one layer the shadow masked.
When i try to follow Morbid Angels solution i come up with a comp like Picture 3
You can see the shadow there is way more prominent and lacks gradients i think because of the lack of GI contribution.
Am i wrong? Does it make sense?

[olika]

Now let`s have a look more into the GI contribution, see next pictures:


Let me explain what i did:
first pic is just the same render (objects invisible etc.) but with GI on (Brute/Lc)
You can see it takes ages to render and it`s splotchy, i never understood why that is happening and can`t resist the feeling it wasn`t behaving like that in the past.

You may ask yourself (and that`s what i also do with this post) "hey why you need GI?, Morbid said do not use it". Yeah but as i tried to show it`s a different result using shadowpass rendered without GI.
The other thing is, why turns Brute/LC crazy when i just change the groundplane to be matte? As long as it`s not matte it renders like a charm.

Now, and thats why i ressurected the old thread, i found out that when i change the GI to irradiance map and no secondary GI than it`s working (see picture 5)
I think you can clearly see the difference in the shadow as the GI shadow pass has way more variation in it (just like the original render)
... huh why is that?
Does that all make sense?

Can`t stop scratch my head about that, as i think using a irradiance map solution is maybe fine for stills but no solution for animation and smells like trying and not fully understanding it
...Anyone? Thanks in advance my vray friends