Few questions about this shadows compositing + Screenshots

[Silverland]

Ok. I am gettin deep into compositing and layers during work with long animation but dont now too much about shadows yet. So have some basic questions.

Guys, please dont hesitate to answer since this is pretty straightforward questions VERY WELL EXPLAINED and i supplied 3 screenshots.

Dont worry about my nodes - since this is just a recombining all the passes together (to remove the noise with help of bilateral blur and determinator only from particular passes) and one group of nodes for glow and blur. Just pay attention on the right panel where i have a three layers -

1 LAYER - ONLY MY ASTRONAUT - WITH NO LIGTHS ( layer 2 - excluded)
2 LAYER - ONLY MY SPACE CORRIDOR - WHICH HAS SOME CORRIDORS EMISSIONS (to lighten up the corridor) BUT THEY ARE EXCLUDED FROM OTHER LAYERS ( layer 3 - excluded)
3 LAYER - ONLY FEW EMISSIONS (TO LIGHTEN UP THE CHARACTER) (layers 1 and 2 excluded)

So first question: Even that i have no shadows passes enabled at all (so they are not combined) i still can see shadows of the character (yes character is not excluded from layer 2, but still…) !!! Is that supposed to be like that, is that how it works?

Second question: Even if i delete third layer where all of the emissions are - shadows are still will be visible. But are they appear even if there is no light source? Is that how it works?

Third question: Even if i enable shadow pass for 2 layer where only my corridor is, and add (add node) it in compositor - i have no control over it. So if i want to change the color or make it strong - i cannot do it though i have access to all other passes which are added in compositor. So what i am missing here. Shouldnt i use add node to add shadows if i want? But all of the other passes are added and i can control them but shadows if i simply add them - not. So how to properly add them as well so i can tweak them?

1 LAYER (LOOK ONLY ON THE RIGHT PANEL)

2 LAYER (LOOK ONLY ON THE RIGHT PANEL)

3 LAYER (LOOK ONLY ON THE RIGHT PANEL)

[kesonmis]

1.Shadow is the absence of light. There is no special “shadow thing” that can somehow be simply captured or rendered. The shadow pass is a try to create a somewhat meaningful element that can be used in compositing to manipulate these areas. How it is actually implemented in cycles, someone else can maybe explain better. The shadow pass does not affect render itself at all. When there is light that casts a shadow, there will be shadows independent of shadow pass being enabled.

2. Without no light sources you would see a black image, so I suspect there are lights afterall. And maybe you are confusing reflection on floor with shadow? It looks similar.

3. Shadow pass is not a light element, so adding it does not make sense. I can’t test it now, but if I remember correctly, shadow pass is white with shadow part being darker. This implied that you must multiply with it, not add. To control, grade it or do whatever you want to control there.

[Silverland]

Thanks. First answer is clear enough now.

Second answer. If i delete third layer with lights… there is corridors emissions lights still in a second layer but…character (so probably and characters shadow as well - i can be wrong though) doesnt supposed to receive this light (because second layer is excluded for the character). And because of that i can see that the character really doesnt lightened up by second layer (otherwise character material will have too much blue on it because corridors some blue emissions)… but characters shadows are still presented in second layer.

Third - But shadows pass of the 2 layer looks completely black if plugged into the viewer node. So you advise to multiply it with image but because its black the output will be black as well. So i still not sure how i can grade shadows in my case.

[Silverland]

And now i found why my shadow does not appear in the viewer node - because as i mentioned in my third layer i used emission materials instead of lamps/ Emissions are not visible for shadows in compositor. Shall use only lamps.