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I try to render a layer that only includes the light as if it was cast onto an object.

But it seams it is not possible to make a material that is invisible for the camera but bounces light from a certain light sources.

To put is simple I want to render a layer that only includes Emssionshader bounces from certain Lights.

best regards,
Wasabi

edit: I hope this makes it more clear what I want. enter image description here

.blend for picture above

edit2: And I already know how to do a Shadow/AO Layer but the light is difficult to distinguish as every pixel I render and is not Black is light. So i only want the Spotlight light but no world bounces or light that is 2-3 bounces "old".

edit3: I faked the effect I am looking for with the asset I am working on. This is maybe a better example than above. enter image description here

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  • $\begingroup$ As far I understand your question, creating an invisible emission material is possible, see: blender.stackexchange.com/questions/17910/… What do you want to achieve exactly? $\endgroup$ – p2or Sep 12 '15 at 13:55
  • $\begingroup$ Imagen a scene with an object that is light with a spotlight. There is nice round light border around the object. Now i want to render that object and the light cast but the ground should be transparent. $\endgroup$ – Wasabi Sep 12 '15 at 14:01
  • $\begingroup$ For the sake of clarity, may set up a simple scene in which one could easly figure out what you are looking for and what are the limitations that prevent you from reaching it? As far the ray hits a surface and bounces back to the camera, is already bringing the light info about the material. Is your problem only about how to put each lightsource in a different Render Layer? $\endgroup$ – Carlo Sep 12 '15 at 14:02
  • $\begingroup$ Ok, what do mean by light border? For the render layers, this great answer: blender.stackexchange.com/questions/3002/… might help. $\endgroup$ – p2or Sep 12 '15 at 14:08
  • $\begingroup$ I have added an example picture what hopefully can describe what I am looking for. $\endgroup$ – Wasabi Sep 12 '15 at 14:27
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I'm quite sure to not have fully understood your question, so before giving you some suggestions I would like to punctualize one aspect (as I have seen you are interested in compositing layers):

No transparency is involved in this scene, dark grey color of the plane/cube in shadow comes first of all from interaction of the plane/cube (diffuse white) with the world background light (which is colored dark grey). All the visible surfaces will produce a white alpha channel area.

You can remove the world influence on the scene by lowering the Background strenght to 0 or even completely remove the shader.

enter image description here

You can set the Max number of bounces of light allowed for each light source in the Lamp panel in the Object Data tab.

enter image description here

You could also tweak the "global" light path bounces, but you'll not have the precise control that the "per lamp" option allows.


By seeing your third edits I would suggest the following (more general) instructions:

  • Switch all lights off (Background too), except the light source you would like to isolate. All the light present in the scene is it contribution
  • Set the amount of bounces allowed for the light source (per lamp, or globally if you are using an emission shader as a per object option is not currently (2.75a) available)
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  • $\begingroup$ What I want is a Layer where are only the information in it how much did this light add light from witch color to this scene. Your second picture is pretty close if i would make the black transparent. but to archive this I would need to make a extra scene with no Environment light. $\endgroup$ – Wasabi Sep 12 '15 at 15:44
  • $\begingroup$ A possible workaround could be to set background strenght to 0 and add a big emitting object (ex a sphere) to substitute it in a specific layer. This way you'll be able to to user render layers to switch off the emitting object. Same thing if you want to have different settings in the lamp object between render layers, but for the global light path there's no other way than make anothere scene. $\endgroup$ – Carlo Sep 12 '15 at 16:41
  • $\begingroup$ Ok thanks I will try that. I hope it will deliver the result I am serching for. $\endgroup$ – Wasabi Sep 12 '15 at 17:02

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