exclusive lighting

(lacilaci86) #1

How do I do this in blender(cycles)? Something like an exclude or include list for lights so that a light only affects single object in the scene?

I’ve read that blender internal had this feature “light groups” that should do something like that, but can’t find a way to do it in cycles.

(Thies Schulz-Holland) #2

You might want to do a forum search for “light linking” - this has been discussed quite extensively.

(Martynas Žiemys) #3

Cycles is not this kind of renderer. You would have to render layers separately and combine them to achieve this. Objects are not lit by the light from the light source alone in cycles, they are lit by the light reflected and refracted by other objects as well. That would make things complicated.

(lacilaci86) #4

Well, that applies to corona aswell and yet it is possible to make light exclusive for an object etc…
Helps a lot when lighting of a scene is already established but an object that appears flat could use some extra light/reflection and so on.
Rendering separate layers and combining them sounds a bit more complicated than a include/exclude list (I haven’t tried that yet though)

(Martynas Žiemys) #5

I would not give up on render layers. That can be more straight forward than it seems and with compositing nodes you get the result combined in the following renders with no extra work. Rendering is also somewhat faster, when unnecessary parts of the scene are masked out in the render layers. It’s so annoying Cycles still samples the masked areas though.

(lacilaci86) #6

Yeah, I guess I’ll have to take a look into layers and compositing. Might be useful in the future anyways.

(lacilaci86) #7

Alright, it wasn’t that difficult and i somewhat like how renderlayers and compositing works…
But I still think that if light or emission node had the option to list include/exclude objects it would be much better, especially if I would want to control several objects and their lighting

(sundialsvc4) #8

One strategy would be – “use BI!” Or, “use BI and Cycles.”

BI is a ray-tracer algorithm that effectively goes from a light-source to see what the light from that source “hits.” If it is a layer-specific light it “sees” only objects in the chosen layer(s). I like to say that it’s a good “spotlight.” (Or, “spot shadow.” Yes, you can have a spotlight that casts shadows but not light.)

Cycles is a path-tracer which effectively searches out in all directions from an object to discover what things illuminate it, and for pragmatic reasons it must consider everything. It uses the GPU to perform massively-parallel computations. It’s a good “soft box.” The lighting is accurate and beautifully even … which can get a little boring.

But you could use the two together, and composite the result – rig spotlights in BI to shine light on exact things and then comp the two renders together. (BI wouldn’t be doing the whole thing – just the “spice.”) This gives you far more precise control of the illumination by leveraging the special capabilities and viewpoints of both algorithms at once. Real-world photographers often use both soft-boxes and strobes for the same reasons.

And incidentally – sometimes what you really want from BI is those “spot shadows” that I mentioned. (Shadow information can also be extracted separately from a render that uses regular lights.) A slight darkening of certain areas, consistent with the presence of a clearly-directional light source, can be exactly what you’re looking for to add a sense of drama and depth to an otherwise-Cycles render, without adding any “light” at all. (You can fine-tune the effect in “comp,” using the shadow data for a variety of creative purposes.)