Tips for fast Iray renders

Oso3D

One of the things I've been tinkering with is how to speed up render times and improve workflow for my comic. And a lot of that comes down to ROI, essentially -- how much does an effect 'cost,' and how much (if any) difference does it make?

It's been repeatedly pointed out that lights have a big impact -- using spot and point lights with geometry is MUCH faster than using emitting surfaces. In fact, you should consider setting surfaces with backscatter or high gloss or similar if you want the surface to be bright but not actually cast light (like 3DL ambient).

But there are other things:

People get really worked up about trying to get good translucence and SSS out of skin, bumps, normals, and so on. But the fact is that unless you are doing a really close-up portrait, many works don't need any of those things. And those lighting effects are COSTLY -- I did a quick experiment with a human figure and some fog. With fog and skin SSS/translucence vs. no fog (which I could add in post), no translucence, no SSS. The first took 3.5x as long as the second, and the difference was pretty subtle even close up at 1000x1000.

I have a figure that basically performs like a blue semi-transparent gel. I switched to just using cutout. The effect is different, and ... way faster.

Textures. While highly textured models are appealing, if you have figures only seen distantly, you might consider using smaller textures or eliminating textures altogether -- at hundreds of feet away, your human figures can have simple one-tone skins.

So consider what you ACTUALLY need in a scene, and cut out what you don't.

 

Any other special tips?

 

Tobor

These are some good points. Height maps (bump, normal, displacement) can also greatly increase render times when the camera is close, as can transparencies, as well as elevated SubD settings for an object or shader.

But I wanted to point our that the spot and point lights don't actually use a geometry, even when changing to one of the other emitter types, such as disc, rectangle, or sphere. While the render may show what appears to be a plane or solid emitter, Iray is instead creating the light programmatically, with no geometry producing the illumination. This allows for faster renders, and smaller scene sizes in memory.