400% render speed increase by LC sample size?

[Micha]

Hi,

it was a big surprise as my render time dropped from 32min to 8min as I changed the sample size from default 0.03 to 0.01. I didn't know that the sample size has such a big influence to the render times. Doe's somebody know this effect, maybe lele ? Also I tried 0.005 but this doesn't changed the speed so much anymore.

I tested 0.01 because I thought 0.03 could be to large. I think 0.01 could be a better default value.

-Micha

[Micha]

I got a note from an other user which I want to quote here:

I think that rendertime change is result of retrace threshold being used more or less. Basically if you dont have enough LC samples, vray will be brute forcing those areas, that`s what retrace is for....

I did one more test in this direction and set Sample Size 0.005 / Retrace 1 and got 6m:47s.

[^Lele^]

Oh, the previous summon didn't work, i read of this just now.
We found that the Max default work well in the most cases: so 1000 subdivs, 0.01 Sample Size, and a retrace of 2.0.
As you well noticed, there may be marginal gains (from 0.01 to 0.005, f.e.), and also potentially big slowdowns (0.01 to 0.03), changing the (max) defaults.
It's somewhat scene dependent, but statistically speaking, we found the defaults to work best, most of the times.
Maybe for the average Rhino scene (which in my mind is about product design, rather than environments. ofc i stand to be corrected.) 0.03 was a good default, then again it may well be it's just an old one.
Our engineers will know what to do, thanks a lot for spotting this.

[Micha]

georgi.georgiev I installed the latest update today and I wonder that the sample size is still so large. What would be the disadvantage to set the sample size at default 0.01 always?

I never used the quality slider and I discovered it today. I don't understand the low max subdivs. For my interiors min/max 1/18 wouldn't be far not enough to get noise threshold 0.01 , the sample rate channel is nearly red - not enough subdivs - and the result is quite noisy. I found that 1/100 is a good setup for all days and only the noise threshold needs to be adjusted. Why is not used a higher subdiv count for the quality slider and the high quality setups?

[Micha]

Here an example of quality slider at very high quality. It's setup I never would use to get very high quality since the output is full of noise. The sample rate shows that not enough samples can be taken to reach the quality level nearly everywhere over the whole rendering. I would say - the quality slider is dangerous, a pitfall for beginners.

The second screenshot show a high quality setup like I use it. The rendering shows a fine noise only, the sample rate hit the max subdiv count of 100 at some areas only.

Maybe I misunderstood anything. Did I something wrong that the default values gave me an usable result? Do I waste render time with my setup? I'm curious to learn more.

^Lele^ , what do you think? Or is something wrong under the hood with the VfR settings? The sample rate help page shows much better results also with low subdivs like 1/18.

[^Lele^]

The very high preset seems to have a bit too generous a noise threshold, indeed the sampleRate shows it clipping max AA subdivs nearly everywhere.
Besides the max AA, it's fine, if *very* high (potential) quality, thanks to that low noise threshold.
If it had higher max AA (like 100), it'd also be very close to being very good for animations as well.

In Max, the LC settings for stills are 1000 subdivs, 0.01 sample size, and a retrace of 2.0, while for animations we suggest 3000, 0.01, 8.0 respectively.
We suggest to never go below a retrace of 2.0 anyway, to ensure there are no LC-dependent artifacts in difficult areas, at the expense of some render time.

[Micha]

Besides the max AA, it's fine, if *very* high (potential) quality, thanks to that low noise threshold.

Interesting, the rendering looks complete noisy. I have the impression at Rhino something doesn't work like expected from 3dsmax. At Rhino the low noise threshold doesn't prevent a strong noise.

[^Lele^]

Interesting, the rendering looks complete noisy. I have the impression at Rhino something doesn't work like expected from 3dsmax. At Rhino the low noise threshold doesn't prevent a strong noise.

I very much doubt that that is the case with 100 subdivs, particularly against a higher noise threshold.
Show me a scene, and we'll be able to debate it a bit better.

[Micha]

I don't mean the 100 subdivs, there is anything fine, that's part of my setup. I mean the current VfR quality slider doesn't allow to get quality for non advanced users. I don't want to know how much new users test VfR and think, it's not usable. Someone from the chaosgroup should check the usability at different scenes. For example at interiors and in GPU mode it doesn't work. I try my best to bring it on the table, now some reaction is needed.

[^Lele^]

We were planning on making adjustments to those presets, we just didn't make it in time for update 1.