I’m creating a glowing spark particle system based scenario in Cycles. It uses an object particle system using Ico spheres as the particles, each one with an emission shader, with various colours, emission and transparency levels based on the particle’s age.
If there’s one thing Cycles hates, it’s small lamps. What better way to make it angry than give each particle emission… The noise coming off it is crazy, requiring a minimum of about 2000 samples, which is still pretty decent I guess.
I was wondering:
1) Would it be possible to simplify the diffuse lighting? I have no idea whether there’s a way of creating a volume-based average or getting the average of a group of particles. I imagine this isn’t possible natively and would probably require scripting?
The other idea I had is deselecting diffuse on the particles and using a few keyframed lamps to give a “rough” lighting estimate, hopefully, good enough to fool the eye?
2) The idea of a particle emitting light is simple and quick to render, but when DOF gets involved the bokeh balls get very noisy. Is it possible to simplify the DOF by just drawing balls instead of tracing each pixel of the ball? There isn’t any way for the light to get blocked in my scene, no need for that level of realism.
Of course, the solution for all of this is more samples… But I’m wondering whether I’m unnecessarily complicating the scene and there’s some sort of optimisation possible. The amount of options in Blender confuse me! This is the only place I could think of posting to, sorry if this is a stupid question. A reply would be much appreciated!
The other idea I had is deselecting diffuse on the particles and using a few keyframed lamps to give a “rough” lighting estimate, hopefully, good enough to fool the eye?
This is usually the way to go. In the vast majority of cases, no one will really notice the difference.
For question #2, you could in theory do this. I don’t think there’s really a good way to do it in Blender though, tools just aren’t set up for it. Post-process DOF is probably the easiest way to handle it. You can dilate out the z-buffer (use the dilate/erode node if in Blender’s compositor) to get some nice blur on your particles. Rendering them on a separate layer might help, depending on how much control over the DoF you need.
I’m sometimes faced with rooms using lots of tiny ceiling spotlights, sometimes alcove (pure indirect ceiling lights) as well. Trying to brute force this results in insane amounts of noise, and I try to cheat the system a bit thinking like this:
Huge area light in the ceiling doing diffuse only, mimicking bounced light from the ceiling. MIS enabled. Can be bounce controlled in light settings.
Huge area light above the table doing diffuse only, mimicking bounced light from the floor. MIS enabled. Can be bounce controlled in light settings.
Smaller emitting planes for rough glossy only, resembling general strips or patches of light sources. MIS usually off, sometimes enabled. Since material, not possible to bounce control. You can’t use light sources unfortunately (which converges faster), because they won’t react to light path node. You can toggle visible to glossy, but not glossy sharp only.
For cove lights I use strips of area lights doing diffuse only, MIS disabled, and 0 bounces. Indirect light comes from a separate light source rather than being actually bounced.
Tiny emitting materials for the actual lights, visible only to camera and sharp glossy. MIS disabled.
Pretty much disable MIS for anything dark and/or which contribute little to bounced lighting.
For environment lighting, I will setup the HDR, and then approximately mimic the result using area lights close to the windows (can’t texture them yet) and a sun light (if present) and still render that one out separately.
I don’t know if I’m thinking about MIS (multi importance sampling) correctly, I could be completely wrong. Things may improve when we get IES lights and UV coordinates for light sources.
This is obviously not very “realistic” and you have to consider using sharp reflections if you want visible lights in the reflections, but I’m still getting images others call “pretty”. Not good for a lighting and material study, but good enough in some cases if that is not the focus of the image.
Many tiny lights? Fake the hell out of it or get a renderer more suitable for that kind of job.