stainless steel noisy

[newages]

morning!

i got a little problem here
most of my scene is noise free - only this one part with the stainless steel mat is really noisy
it is a blend mat with a custom falloff in the reflection slot and the typical brushed steel bumpmap
blended with one more and one less glossy reflection
the reflection is from an ies-spot in the ceiling

is there a way to optimize just this one material or do i have to render everything until it gets better?

best greetings
rene

[romullus]

Pretty sure, it's bump map. It's better to replicate brushed steel with glossiness map alone. Leave bump mapping for broad surface irregularities.

[Juraj]

Romullus advice is sound, I too use micro-brush bump only in very close-up. In all other cases, it's only glossiness map.

But it's also a general rendering problem, where metals take more to sample than general material due to their high specular reflectivity, and also because they're reflecting high-intensity small speculars like the IES light.
Sometimes it's good practice to avoid the light affecting speculars and instead use some lower intensity emmissive to that job (not instead ! but purely for the reflection/speculars).

And last, well, there isn't proper adaptivity yet so either sample whole image more or use a mask to sample just that area. Is your MSI default too ? (should be).
But try all the things in steps.

[newages]

thanks for the tips guys - they helped a lot
in the end the image turned out a bit different:

https://forum.corona-renderer.com/index.php/topic,5038.0.html

[twoheads]

Romullus advice is sound, I too use micro-brush bump only in very close-up. In all other cases, it's only glossiness map.

But it's also a general rendering problem, where metals take more to sample than general material due to their high specular reflectivity, and also because they're reflecting high-intensity small speculars like the IES light.
Sometimes it's good practice to avoid the light affecting speculars and instead use some lower intensity emmissive to that job (not instead ! but purely for the reflection/speculars).

And last, well, there isn't proper adaptivity yet so either sample whole image more or use a mask to sample just that area. Is your MSI default too ? (should be).
But try all the things in steps.

Hello Juraj, could You write a bit more about masking an area instead of whole image You've mentioned?

[Juraj]

MaskID (or how it's called) pass in Corona :- ) It generates a mask for each material in pictures.

 Region crop to over-sample your noisy slot. Then use MaskID to swap that material in Photoshop.

Yeah it's not pretty...

[twoheads]

Yep, it's not but it should work pretty fine, thanks.

Btw: how do You usually cope with nasty noisy stainless steel in your renders?

[twoheads]

in addition, do you render out whole image with "default settings" to get things faster and then render out steel and composite both images in PS?

[Juraj]

Well I actually rarely do that.

I've already learned not to use too complicated shaders in full-on architectural scene. A nice shader with hi-res maps will render fine everywhere (like studio setup, close-up,etc..) outside of complicated interior. There..I can simply go fuck myself.
So my solution at the moment, and for the past months, has been to simplify shaders in this scenarios. Is the shader small in camera and produces far too much noise ? Simplify&Fake it.

Also, I rather oversample renders. Maybe they are ok-looking at 200 passes but I still let them cook for 400 to get rid of any avergeable noise. If there are some parts that would be clean in 1000 passes, I just de-noise them in Post.
I don't do that composition which I offered as solution myself. That's the kind of workflow I absolutely hate with passions. I would do that only in absolute desperation :- ).

But I also don't use micro-bumps for metals. I don't know of ray-tracers that cope well with this (but there has recently been cool research paper posted about how to improve this, even to use normal maps for micro-glint like scratches !).
All the details are in glossiness map.

[twoheads]

Yep I also hate compositing and this kind of stuff but You know, sometimes You have no choice.... anyway, I found stainless steel the most problematic material so far (in certain circumstances).   Basically sometimes it works without problems, sometimes you need to spend way too much time on it.

thanks

[Juraj]

I absolutely agree on stainless steel. It's very specular materials (like metals) that are very hard to sample when other conditions get introduced (like GI) in Corona.

1) Metals in studio/exterior/etc... = Super fast, super clean.
2) Diffuse or just low specular materials (insulators like wood, plastics,etc..) + GI (interiors) = Decently fast, can get super clean as well.

1+2) Interiors with rough (anodized, brushed,etc..) metals = Never gonna sample to clarity. It will always be slightly blurry and noisy. Forever and ever.

I don't want to say this is somehow purely Corona's fault. Same situation is complicated in Vray as well, but with either adaptivity or simply settings more sample (either directly in material or through min. shading rate feature), you can solve it.
In Corona there is no solution like that, so it's either you wait forever and oversample rest of the image by 10fold, or you selectively over-sample those parts in region render.

[twoheads]

I believe it's already on the wishlist but would be nice to have "lasso" selection tool  in the future to render out precise area. Region render works fine but in most cases it renders additional unwanted space.

[twoheads]

On the other hand, in mental ray it's quite easy to setup stainless steel and it looks great but it requires ultra high material sampling which obviously causes dead long render times... you wait..and wait....and wait ;)