Progressive sampling - noise threshold?

[peterguthrie]

sorry for the probably dumb question, just wondering how the progressive sampler noise threshold and the DMC sampler threshold are linked, or related to each other?

If i set the DMC threshold to 0.01, and progressive to 0.0, what happens? does the render stop when it reaches the higher of the two, or carry on forever?

thanks in advance!

[Dariusz Makowski (Dadal)]

If progressive is set to 0.0 then render stop when either time limit is reach or number of passes.

DMC sampler Threshold is not limiting the render time of Progressive threshold I think.

[peterguthrie]

but what happens if the DMC threshold is pretty high? if the progressive isnt limited by time, passes or noise does it just keep on rendering and not getting any better anyway?

sorry for being thick, just havent got my head round progressive yet

[Dariusz Makowski (Dadal)]

Umh well if he is not getting any better then you need to increase your material/lights/gi/etc samples or increase the multipliers in dmc settings... I think - not sure haven't done too much of progressive tests...

[peterguthrie]

really i just want to know what the workflow is for using progressive, anyone using it?

[alexyork]

really i just want to know what the workflow is for using progressive, anyone using it?

I just used it on a job and it's all quite confusing, although I got great results with it and it really sped up my testing phase. I hope that Vlado or someone else from Chaos (or anyone else) would do a quick write-up about the whole PM workflow.

[peterguthrie]

well glad its not just me who is confused!

any chance of a step by step guide anyone?

[Dariusz Makowski (Dadal)]

Isnt it exactly like DMC Adaptive with its threshold works? I'm pretty sure thats how they are linked.

[vlado]

but what happens if the DMC threshold is pretty high?

The DMC threshold is used when V-Ray needs to fire multiple samples for secondary effects like area shadows, glossy reflections, GI. It does not control when the progressive sampler will stop. The progressive sampler only looks at its own noise threshold which it uses to compare pixel values.

If you use the progressive sampler, it would be best to leave all settings in the DMC sampler rollout to their default values. In fact, I very much want to hide them away somewhere so that people don't get tempted to touch them.

Best regards,
Vlado

[alexyork]

The DMC threshold is used when V-Ray needs to fire multiple samples for secondary effects like area shadows, glossy reflections, GI. It does not control when the progressive sampler will stop. The progressive sampler only looks at its own noise threshold which it uses to compare pixel values.

If you use the progressive sampler, it would be best to leave all settings in the DMC sampler rollout to their default values. In fact, I very much want to hide them away somewhere so that people don't get tempted to touch them.

Best regards,
Vlado

Sounds like a good idea.

So, let's take an example scene - everything is rendered to an acceptable level of noise except for certain areas of the image - some pools of light on some floor areas. Is it safe to assume that the solution to this is to whack up the light's samples? I had this example recently and was struggling with PM. The whole image seemed to render to a good clean level after only around 10 mins but certain areas were still very noisy, where there were vray lights directly there. Even light samples at 400 or more were still extremely noisy compared to the rest of the image, including areas of large glossy reflections.

[vlado]

Is it safe to assume that the solution to this is to whack up the light's samples?

No. It might have been due to the probabilistic light sampling if that was enabled.

Best regards,
Vlado

[RockinAkin]

Someone please chime in if you feel I'm wrong, but I feel the confusion stems from the Image Sampler's UI being a bit of a mess at the moment.
Fixed, Adaptive, and Progressive should all be merged to share the same general UI layout, since they're all just variants of the same sampler.

Present one UI for setting Min and Max subdivs / Noise Threshold / Use DMC Thresh / etc.
Then if someone wants fixed sampling they set the Min and Max Subdivs to the same value and the rest of the options become disabled (grey out).
And if someone wants progressive sampling, they check a 'progressive' checkbox, which enables the Render Time and Ray Bundle settings.

That way it's instantly clear that they're dealing with the same sampler - just different ways of working with it.

[vlado]

Fixed, Adaptive, and Progressive should all be merged to share the same general UI layout, since they're all just variants of the same sampler.

Present one UI for setting Min and Max subdivs / Noise Threshold / Use DMC Thresh / etc.
Then if someone wants fixed sampling they set the Min and Max Subdivs to the same value and the rest of the options become disabled (grey out).
And if someone wants progressive sampling, they check a 'progressive' checkbox, which enables the Render Time and Ray Bundle settings.

That way it's instantly clear that they're dealing with the same sampler - just different ways of working with it.

While it's not a bad idea generally, I don't know if it's any less confusing. Besides, it looks like many people are using the progressive sampler for previews as they work, and switching to Adaptive for the final render. In that case it helps that they have separate settings.

Best regards,
Vlado

[Neilg]

Besides, it looks like many people are using the progressive sampler for previews as they work, and switching to Adaptive for the final render. In that case it helps that they have separate settings.

this is what i do. I couldnt imagine trying to use progressive for a final - seems a bit too fiddly to figure out when it should stop.

[RockinAkin]

Besides, it looks like many people are using the progressive sampler for previews as they work, and switching to Adaptive for the final render.

But I would think unchecking the 'progressive' checkbox in my example would basically accomplish this.
The user would have progressive checked while doing previews, then uncheck it when they want to switch back to bucketed mode for final renders.

It would be less confusing to newer users who come into V-Ray thinking there are 4 separate image samplers that all work in different ways.
Even some professionals I speak with still think Progressive is a totally different sampling method compared to Adaptive DMC.