Hello all. I am just getting back into CG after a long hiatus. I used Maya back in the 90’s, so still learning the new tech and Blender. But what a change!
I am doing a practice scene with a small camping scene and a camp fire. Got most of that going, but now into the lighting. I like the look of the fire, but want to add some more fire light onto the other objects with out affecting the ground near the fire. I would normally use separate lights for each object to be able to control it more precisely. I know I can animate the strength, but I would like to have it “automatic” so I can link several lights to the same values based on the flame intensity.
It’s been awhile, but (IIRC) I used to connect the flame output to the lamp intensity input via nodes.
So basically can I somehow get the value of the partial emission and connect it to the light node intensity? Does the make sense?
Sounds not like the easiest way to do it, IMHO. Wouldn’t know a way to get the value of the total light emitted by a fire.
My idea would be to use render layers. Then you can use the ‘real’ light from the fire but with different intensity/material settings for different light paths. The way I see it, you have three different paths of light you want to treat differently:
‘direct’ light from the fire
light scattered on the ground to the eye
indirect light from elsewhere
If you set the holdout flag on a collection for a view layer you make the objects inside appear black to the camera but still contribute indirectly. So you would put ‘differently lit’ objects into different collections which are active only on one view layer each (and set to holdout on the others). The full image you can obtain by adding the intensities of all view layers in the compositor.
The different lighting you would get by changing the material settings for the fire/smoke domain for each view layer. Unfortunately that is a little bit of a nuissance to do, as it cannot be set directly (per object). What works for me is:
do a ‘duplicate linked’ of the smoke domain for each view layer and place these in the corresponding collection
in the material tab change the ‘Link Material’ from ‘data’ to ‘object’
make a copy fof the original material for each copy of the object, so you can tweak it independently
one further obstacle with the smoke sim is, that ‘duplicate linked’ only links the sim bake, when ‘External’ is checked for the cache.
I am still new to Blender, but I think I follow your thought process on comp’ing different layers of exposure. That would work, albeit with several extra renders.
I am thinking maybe to create hidden planes as emission sources and “project” a fire image off them onto the objects. Sorta like a TV illumination trick.
Again, thank you - and all I have learned from B.A.
I used a texture node with a animation mpeg of a quick closeup render of my fire (that I trimmed and blured a bit in Premiere). I connected it to the lamp Emision (Color to Color, Alpha to Strength) with some Math Nodes in there to tweak it.
It works very well, and I can quickly duplicate and add to several other “accent” light in the scene.
