Optimal cycles settings for raytrace rendering?

Hi all, I was hoping to learn how to optimize the mysterious cycles settings (“integrator settings” “seed”, “ray bounces”, etc) to get a nice quality to speed ratio with raytrace renderings. Anyone have any tips for settings? Thanks

@nathanletwory

Seed is something you don’t really need to worry about. The seed is used for the random number generator, changing the value doesn’t have any impact on speed.

The integrator settings govern how the raytracing is done. Maximum bounces is capping the amount of total bounces a ray can make. These are best explained in the original Cycles manual: https://docs.blender.org/manual/en/latest/render/cycles/render_settings/light_paths.html . In our options interface we call them Ray Bounces, in Blender they are Light Paths. In all cases lower values will mean faster, but that will be at the cost of fidelity. What each type of bounce / ray contributes to the rendering is explained quite nicely here: https://docs.blender.org/manual/en/latest/render/cycles/introduction.html#light-rays

I suggest you do a test with a scene that is typical for your work and set all bounces to 0. Turn of skylight and have only one point light active. You’ll see that you get pitch-black shadows, and reflections in metal-type surfaces look just black. The lighting is harsh.

Now set all bounces to 1, toggle Raytraced mode and observe the shadows. They already get some depth. But you’ll see in reflections diffuse objects, but reflective objects look awful. So do glasses. There is no real indirect lighting going on.

Bump all bounces to 2. You’ll find that glass materials start to look better. You can also notice indirect lighting between diffuse surfaces (color bleeding, if you will). Reflections start to improve too, but you notice that two reflective objects reflecting each other will start showing black after the first iteration.

Bump all bounces to 3. More indirect lighting, because light can bounce more around, yet improved glass and reflections. In recursive reflections you can see one more object, then black again.

Quality depends on your scene and how you light it. You will want to play with the bounces, have them as low as you can accept for a render. Higher gives better, but beyond some settings it may be hard to tell the difference. But upping the numbers means more rays. And each ray takes time to process.

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FWIW In the future there’ll be adaptive sampling. That would mean that you could set bounces pretty high, and the Cycles engine itself determines when to stop (pixel and neighbouring pixel changes fall below a certain treshold).

Oh, one thing I forgot to mention: the setting throttle ms is a bit of a hack really. It is the time in milliseconds between each pass. So if you want faster, and don’t mind potential slowness of OS response you can set it to say 5 or even 0.

Big thank you for this. Ill be testing with your suggestions as soon as I have a moment!

When you say “all bounces”, do you mean the six options under the “ray bounces” category: max bounces, diffuse, glossy, tranmission, volume and transparency. ? So I should be setting all those to 0 and then increase them all by 1, then 2, etc?

Yes. That way you can see how those affect the raytracing and the quality thereof.

Thanks Nathan

Ran a bunch of tests and here are the results in case anyone is interested. Seems like these settings are the best minimums at least for this one model of mine:
max bounces: 3
diffuse: 2 (a 3 or higher makes the scene too bright…adjust this one to change scene brightness)
glossy: 1
transmission: 3 (raising it above 3 didn’t make a difference)
volume: 1
transparency: 1

I tried making the glass more transparent by changing the glossy/volume/transparency but they didn’t do anything.

RAYTRACE%20TEST%206 RAYTRACE%20TEST%207 RAYTRACE%20TEST%208

Regarding your glass the best to do with Raytraced is to use the Glass material, if you already aren’t. Then remember that the color acts more like a filter. So if you want say an orange glass you have to make the orange lighter if you want the glass ‘more’ transparent.

I see often cases where a user uses a Custom material with a mid-grey at say 50% transparency. But that is not how Cycles works. There we have a Glass BSDF in use which is always 100% transparent. The darker the color, the less light passes through. Create a set of glass materials ranging from white gradually going to black over the greyscale. Have a simple plane with a tiny bit of thickness (important), ArrayLinear it so you can assign each material on a plane. Enable the sun, and ensure you have the default material on the ground plane. See how the glass behaves with the light.

Thanks man, Ill give it a shot during some down time.