render layer system help please

[darkline]

Hi,

I don't know if this is a bug or simply I don't fully understand the render layer system, but if so I'd really appreciate some help.

I have a moving background shot which I need to composite a cg character in, so firstly I've tracked the shot with Syntheyes and imported the camera into 3dsmax. Next I've created all the proxy objects which are used to catch shadows of my charatcer, and sculpt the light. Mainly the floor and several walls. All these proxy objects, which will not be visible in the final render, I've assigned to layer 2

Next there are 2 lights in the scene which ive left on layer 1 along with my CG character.

Finally ive added a layer shadow pass in render elements, and enabled 'render layers' to 1.

Here's the problem: When my character runs behind a wall it does act as an occulsion for the light source which is good (my character goes into darkness), but the shadow is still cast like there is no wall present to block it. On the shadow pass layer i can see this shadow being cast on my proxy surfaces even though theres no way it would be casting one (because there is a wall blocking the light).

At the start of my shot i can clearly see my character is casting 2 shadows in the scene, however one of those shadows should not be there as the light is behind another wall - it's almost as if the light is passing through the walls to create the shadow even though the illumination itself is not passing through the wall.

So is this a bug, or is there a setting or workflow that I'm missing? I have 2 lights in the scene because as my character moves along he goes from being illuminated by one light in one room, to another when he passes through a door. Even though my proxy objects block the light on the beauty pass I can see both these shadows throughout the shot on the shadow layer.

If this sounds confusing i can post some stills to illustrate.

thanks

[darkline]

here's a basic example :

Perhaps I'm not using this correctly, but shouldn't the ID1 shadow pass contain all the shadows cast from ID1 objects onto ID2 (including any occlusion)?

[paride4331]

Hi darkline,
I do not think there's any issue, maybe I did not understand what you say.
attached a quick test.
Regards
Paride

[darkline]

Hi Paride,

Yes I think you have missed my point. What you showed me was a 'shadow pass' and not 'layer shadows'. Shadows pass includes all sorts of shadows you don't want in the composite.

I only want to include the shadows of layer 1 cast onto layer 2 (because shadows already exist in my VFX background video). If I composited a 'shadow pass' onto my footage it would look wrong - have a look at my original post to see the background image with all it's lighting/shadows and how I built proxies to mimic the same thing in max so that the same lighting and shadows fall onto my character (or spheres in this example).

So when you render out a beauty pass from Layer ID 1 you also add 'layer shadows' as a render element to see the shadows ID1 casts onto all other layers. However, i think the bug is 'layer shadows' does not occlude the shadows from other objects like it should - hence double shadows which are look wrong in the composite.

Unless of course the workflow im using is wrong.

[paride4331]

Hi darkline,
I did not understand, I read in your screenshot "shadow pass" so I thought you talked about shadow pass issue.
shadow pass is a new pass, it shows all the direct light shadows that calculated on the first bounce.
to make compositing you need shadowpass and shadow layer together.
Regards
Paride

[darkline]

Hi Paride,

Now Im a bit confused, you're saying i have to use the shadow pass and layer shadows together to get the result i want? How does that give me the result i need? Thats confusing as i cant get any pass to show the correct shadows in the scene. Can you please show me how I get the correct shadows i need from the original post?

In my opinion the layer shadows does not fucntion correctly as it does not occlude the shadows from the light sources and walls, and the shadow pass has all the shadows on which is no use either.

To me this seems a simple question, i want to see the shadows from layer id 1 onto objects layer id 2 but they have to respect occlusion from the walls also. Is this possible and if so how?

thanks

[paride4331]

Hi darkline,
I apologize, I made a mistake, I never used shadow pass when released, so reading about this layer, generated by the first bounce, I thought was split into multiple shadow layers.
Said that, i did some tests to understand your issue. i think shadow layer is correct, maybe it seems incorrect but it should be right.
I created this scene and made tests, looking at the light, the shadows generated seem more and moving the lights, you can understand how and why the lights and shadows seem incorrect.
Regards
Paride

[darkline]

Hi Paride

I think you're still not quite understanding my problem. Remember my background video/image already has shadows on it from walls and lights. I dont want to see extra shadows on my render which already exist in the video. In the example you posted you can still see all the shadows from the doorways on the render which you would not want on the composite. You would only want the shadows from Layer id1 falling onto layer Id2

The way I've been working is setting up my Cg character as layer ID1 and my floor as layer 2 - this all works fine when there is a single light in the scene and a floor, but as soon as you get into sculpting the light with object occlusions the system doesn't work.

shall I try to make a video to explain clearer what the problem is? effecitvely if you turn render layer soff all the shadows look correct because they are occluded by walls, however when you turn render layer back on the walls stop acting as a light blocker.

In the example you posted you are doing things very differently. Your shadow layer comes from changing the render layer ID to 2, instead of 1. the way Ive been working is leaving the layer ID on 1 and assigning floor and walls to 2, leaving the spheres on 1 . This should give you a correct beauty and shadow layer in a single render pass, but it does not.

[darkline]

Ok here's a video which I hope explains what I'm trying to do and why the layer shadows may not be functioning correctly. Or maybe It's I'm using the wrong combination.

However I do believe this can be done as you'd need to do this for almost all VFX shots in a film.

Hope you can help!

[darkline]

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