Increasing quality -> reducing rendertime

[toby™]

Good morning fellows.

Yesterday, my day ended up with a rendered image that took about 35min to be rendered. But all I got was a noisy one. Noise? No problem, if it isn't too much as in this case.
I question for your suggestions on how to improve my scene in terms of rendertime and improved quality.

Simple scene with 3 V-Ray light planes, 1 dome-light with an HDRI linked to it and a modeled background with "Not visible to camera" option turned on in its object properties. Not being forgotten, my V-Ray Camera

Thanks in advance.

-toby

[instinct]

Can't look in-depth atm. One thing that pops at me right away is that you might wanna get rid of the Lanczos Filtering. Lanczos is a sharpening filter wich will pronounce noise

Regards,
Thorsten

[toby™]

Hi Thorsten!

Thanks for your tip. I've given it a shot, but noise won't go away, even with another AA filtering option like 'Area', 'Video' or even 'Cubic'. Will try, if it is the HDR-Image that causes V-Ray to produce such a noisy result.


toby

[themaxxer]

In most cases it's the domelight. try to increase the sibdivs to 24 or more...
I think it needs more samples because of it's size = lightsource.
hope it helps.

best regards
themaxxer

[toby™]

Hum... frustrating...

Never had these issues before


toby

[bardo]

for the rendertimes check if you have many burned areas (use the "force color clamping" button to visualize the area where your value exceed the float value of 1.0).

High float values over 1.0 force the antialiaser to do much work.

[toby™]

Well, color clamping might be helpful indeed. And, I guess I've found the noise producing item in my scene. It's the HDR-Image, causing noise in its reflected bright areas O.o

toby

[^Lele^]

In general, when using DMC AA, you can try and turning filtering off entirely, if the sampling is high enough (say, 2-8, or higher).
As well, DMC AA will try and compensate for undersampling in other areas, behaving as a "generic" ray.
While that's nice and desirable, it's also a wee bit slower than having the individual effects be clean BEFORE AA kicks in.
Try AAsing a render with a noisy domelight, and one with a clean one, and compare rendertimes when it's the AA doing the cleanup versus the Dome light itself.
You should see the benefits right away.

[rivoli]

in this case you can try to compensate for the noise raising the mat's reflection subdivisions. as long as I can tell all you have in scene are glossy reflections after all.

[simmsimaging]

You may also need to raise the subdivisions for the camera DOF.

b

[voltron7]

+1 for the clamping/sub-pixel mapping. I notice significant reduction in render times with both of these checked.
Also, I had a similar thing happening, and it was greatly helped by turning off the VRaycam DOF for drafts, so maybe try Brett's idea, too...

[^Lele^]

Clamping will greatly reduce the dynamic range of your renders, cutting whites to 1.0 float.
That means that if you'll try and expose the picture in post, your whites will turn gray, instead of dimming properly.
Just so you know what you'll be facing if the clamping option is active.

[voltron7]

Great info LeLe! I have tried both ways, but I guess I don't really do too much severe post work to notice my whites getting gray.
But now, at least, if it ever happens, I'll know why

[raymarcher]

You can always clamp above 1.0, when clamping around 5.0 - 6.0 you still have aprox the dynamic range of film

[^Lele^]

indeed clamping can be set higher than 1.0, but that defeats most of the speed-up.
The idea is that VRay will try hard to AA overbrights, and make sense of them in glossies.
If you clamp to 1.0, that reduces the DMC sampler's work a wee bit, which isn't the case for a clamping @ 5.
Ofc, it IS a lot better than not clamping if you have very, very bright stuff around (a visible sun, or a lightsourcevisiblevisible lightsource @, say, 30.0 float).