Arnold, Is this noise or intended?

[-niels-]

@Alfred.DeFlaminis, @faline.custodio.da.silva

I've been recreating an old render i did a few years back, but with Arnold and all the new stuff i've learned along the way.

The thing is, whenever i do Arnold renders that are lit with Arnold lights instead of the IBL (environment) i'm fighting with the settings for reducing the noise. (most often specular noise)

For this render i had everything set up and the active shade preview render looked fine.

When i set it to production render at full size it suddenly had lots of specks/fireflies/noise in the glass.

Those didn't show up when i rendered the scene with IBL also active.

Actually, just look at the images... was going to use this in a Friday pictures, but problem solving comes first.

This one is lit with skydome (no volume) and the spotlight (with volume) and the option for IBL (scene environment) active.

This is lit by the skydome (no volume) and the spotlight (with volume) with the option for IBL (scene environment) deactivated.

The atmospheric volume in there is why i don't want to use the IBL contribution to the light.

But i'm unsure if the specks are an effect of the volumetrics or truly noise that i can still remove.

In the active shade's AOV's i had the most problems with noise in the indirect specular.

I realize this could be as simple as increasing the volume samples, but with an hour and a half of render time for the full size... i'm not in a position to try a lot of things fast.

The lower resolution Active shade preview doesn't show enough detail in this case.

So i could really use some suggestions on how to tackle this properly.

[Alfred.DeFlaminis]

Hello @-niels-,

It can be difficult to diagnose lighting scenes without the project files.  Would you like me to create a private folder?

Generally speaking, volume lights and volume rendering have always been slow.  How big is 'full size?"  If you turn off the volumetrics and check your elements (aov's), is the noise less for that pass?   What is contributing to the secondary (indirect) bounces?  (Just a ground plane?)  Thanks for the info!

Best Regards,

[-niels-]

Hey @Alfred.DeFlaminis,

I won't mind sharing the scene with you, so set up a folder if you like.

As for your questions:

Full size in this case is 1920 x 1080.

I haven't tried without the volume light yet, as mentioned it did not show in my (800 x 450) preview render.

I'll give that a try tomorrow if I get a chance.

There is only a ground plane as you suspected.

It is set to almost full metalness and almost full specular with some roughness.

I did turn down the indirect specular a bit for it to relieve some of the noise I was seeing.

[Alfred.DeFlaminis]

Thanks for the info @-niels-.  I'm guessing that it does just need more samples for volume rays.  Tweaking and optimizing volume fog/light can be tough and it's definitely a resource hog.  What CPU are you rendering with?

I have set up a private folder for you if you'd like to upload your files there. You should get an email about it shortly, and if you don't see it please check your SPAM folder. These files are private and will not be shared with anyone but yourself and the support staff. Please let me know if you have any questions. Please use at least an 8 character password or the Box account may not work properly.

Best Regards,

[-niels-]

@Alfred.DeFlaminis I've uploaded the scene and the required hdr image to the Box.

I rendered this on my work pc which has a Intel i7-3770 at 3,4 GHz.

I do have to add that i was letting it render in the background while working in Inventor, so it might have taken a little longer because of that.

(Resource hogging was definitely noticeable in Inventor )

I tried with removing the atmosphere and the specks still showed, i added a few more AOV layers and found out that the specks are in the "transmission_indirect".

Cranking up the transmission samples doesn't seem to fix it though, so i hope you can tell me where to look.

[Alfred.DeFlaminis · Accepted solution]

Hello @-niels-,

I checked your file, render looks totally different to me than your first image but it is what it is.  I don't see a good reason to use the transmission scatter on this glass.  It's primarily used as a liquid fog color.  When I change it back to black, the problem instantly resolves.  If you don't want your glass totally clear, just reduce the general transmission color a bit.  The tramission scatter is primarily for things like honey or deep water.  Can you please try that for me?

I also got some improvements by using "Exit to Background" and increasing the depth.  

Best Regards,

[-niels-]

@Alfred.DeFlaminis Hah, that's it!

I did play around with the scatter before i had a spotlight and atmosphere in place in order to get some shadow from the glass, did not know that scatter would have this effect.

I should probably have read up on it, though i kinda forgot i had set it in the first place...

Using the depth and tweaks to the transmission color do seem like the better way to achieve the same effect without creating those specks.

I'm a bit surprised that clear glass doesn't cast shadow, but i suspect that might actually have to do with the "depth" as it is pretty thin glass.

Oh and i was going for the look of the 2nd image, the first had IBL contribution enabled which cast a double shadow with the spotlight.

Thanks again for helping out with this, you're the best!

[Alfred.DeFlaminis]

You humble me with your kind words @-niels-, thank you, sir.   It also tripped me up that pure white transmission kills the shadows, MR used to do that too.  It's just a different way of thinking.  I suppose pure white and pure black or more concepts than realistic settings from a conceptual standpoint.  Thanks for the update @-niels-!

Best Regards,