Glossiness Settings vs. Render Times

[Marshall_Craft]

I just recently discovered the glossiness setting on the Vray Material Editor (too many things to learn.) Anyways, once I adjust it to where I want the reflection to be, my rendertimes start to increase quite a bit. Is this glossiness controller related to or the same as the options related to "glossies" in the Vray object properties and in the Render dialogue box? I've never fully understood where the glossies were coming from, and now I need to understand and start my final render SOON.

Sorry for the noob question (those are the only ones I have...)

Here is an earlier test render of the effect and my mat and render settings. My GI settings are low just so I can work out my materials before starting the final render, but I'm open to suggestions on any and everything shown here.


[img][/img]




Any and all help is greatly appreciated (especially if it comes quickly...)

- Alex

[dapeter]

The glossy look on the material comes from the Refl. glossiness setting in the VrayMtl. This is a percentage (from 0-1) with 1 being fully reflective (no glossy effects) and 0 being... hmm, I have no idea, I've never turned it down below 50.

Anyway, it does greatly affect the rendertime, since Vray has to subdivide each point sample to determine the glossy blur. The number of samples of the glossy reflection is the 'Subdivs' setting in the VrayMtl. Just like everything else, less subdivs = faster rendering. Also, usually for glossys I limit the reflection depth to 2, since after that the reflection gets lost in the glossy 'blur'.

One thing you can do is use Adaptive QMC for the Image Sampler, it tends to work faster on glossy materials. You can also adjust the QMC Sampler for quality/speed - for instance, for test renders set the Image Sampler to 'Fixed Rate = 1' and the QMC Sampler to 'Adaptive = 1' 'Noise Threshold = .01' 'Min Samples = 3'.

Then there's the Use Interpolation checkbox... this turns on the 'Reflect Interpolation' settings in the VrayMtl. It will prepass whatever the Min/Max rate is, so if it's set at Min = -3 and Max = 0, Vray will run 4 prepasses on the image before rendering. Sometimes speeds things up, sometimes doesn't, but if you don't check the Use Interpolation box you don't have to worry about these settings. There's more info in the help file, and I think some samples too.

The other two things that affect glossys are obviously the glossy effects toggle in the Global Switches rollout, and the Global subdivs multiplier in the QMC Sampler. So, if you have a glossy material on the floor with subdivs set (in the VrayMtl) to 6, and change the Global Subdivs Multiplier to 3, it's the same (basically) as setting the subdivs to 18 in the VrayMtl. It does multiply more than that, though, so sometimes it's better to just set it on a per-material basis.

As a side note, the image looks washed out / foggy - have you disabled the Exposure Control in the Environment and Effects panel? Vray doesn't really get along well with it.

[Marshall_Craft]

thank you so much for the quick, thorough response. This definitely helps me understand what I'm doing and how it's affecting my render times (and images.)

no exposure control (linear color mapping though; still need to learn how to use OpenEXR to composit thought.)

Again, thanks!

-Alex