What's the best way to render dark scenes with minimal light?

[dylan86.exe]

On it, thanks!

Any luck Le Le?

[^Lele^]

Not yet: it wouldn't work at all for me, but it did work right away for someone else.
We're still looking into it, so to make sure we aren't missing something.
Sorry for the delay, it's a bit of a hectic time. :P

[dylan86.exe]

Not yet: it wouldn't work at all for me, but it did work right away for someone else.
We're still looking into it, so to make sure we aren't missing something.
Sorry for the delay, it's a bit of a hectic time. :P

No problems at all. Thank you for taking the time to look at it!

[Micha]

Hi,

today I was so unhappy about the noise at dark areas that I longer think about it. (I'm using Vray 3.2 at Rhino.) I found the reason and the simple solution. My fault was to render with output gamma 1 and to use the frame buffer sRGB mode. (Is it not the linear workflow?) In the past I used output gamma 2.2, but in the last weeks I jumped to output gamma 1. The problem is that the automatic sampling decide to set the sample count on the brightness without any post changes. Dark areas are less sampled. But per output gamma 1 the image is extreme dark and if the enabled sRGB output is enabled in post, than the dark areas are brightened and the low sampling is visible.

Maybe I understand something totally wrong, but I'm glad to get my dark textures and shadowed areas noise free again without to set strong noise thresholds. So, the conclusion for me is, avoid strong changes at frame buffer post level, also the be careful with the enabled sRGB button.

[dylan86.exe]

I haven't heard back from anyone regarding my problem. I've tried every setting under the sun and unfortunately this is the best I can possibly come up with - it's a little embarrising! I'm better than this! But I don't know what to do other than add more lights (which I don't want to do because the scene wont be realistic in lighting regarding the real world room it's based off)
If this is a limitation of Vray (low lighting) then I'd like to know for the future so I can avoid this type of mess!

I've attached Raw lighting, Final render and Final with Post.

[Micha]

Did you need to enable the sRGB button at the frame buffer to get the shown output?

[^Lele^]

I've found out what it was, and my original hunch wasn't too far off (in that i thought it had to do with the colormapping), but boy was i not led into a merry chase! ^^
Let's go step by step, however:

I haven't heard back from anyone regarding my problem. I've tried every setting under the sun and unfortunately this is the best I can possibly come up with - it's a little embarrising! I'm better than this! But I don't know what to do other than add more lights (which I don't want to do because the scene wont be realistic in lighting regarding the real world room it's based off)

I am not sure how "physical" your scene is: you have an omni light suspended mid-room casting sharp raytraced shadows.

Further, you're emitting twice, once from the spherical lights, and once, and in GI only, from the lamp shades. Make sure it's what you want, for i doubt you have a light in front of a light at home.
Using lightMtls in non-direct mode also tendentially leads to excessive work for poor results, but that's a different topic.

The third mistake was wityh your light intensities (more on this later), way too low, for which you overcompensated with the exposure settings.
In fact, if you turned exposure off, most of your scene would return pixel values below 0.001 (ie, always 0.000 for Value. see attached image).

Last but not least, while i miss the bitmaps, i can see that you're manhandling reflections and diffuse with non-physical falloff map modes.
It's really not ideal, as that map has serious age issues, including precision, besides the fact that you force light to bounce in very unorthodox ways (there is only Frensel in the real world. Varying, surely.).
Best you can do is stick (especially for stuff like plaster walls) to a GGX BRDF with glossy fresnel enabled.

If this is a limitation of Vray (low lighting) then I'd like to know for the future so I can avoid this type of mess!

It is, i am afraid, a limitation in current precision achievable with floating point numbers.
There is little than can be done to recover the loss of info at the edge of the precision through multiplication (what exposure does).

So, solution?
First, make sure your lights are of the correct size, and emissive intensity (for that, use IES profiles, or research the lm the light emits, and match it in the V-Ray lights with the provided units.)
You had it about correct for the spherical lights, at ~1500 Lm for a multiplier of 5.0 , but you have covered (ie. shadowed) them with the lightMaterial, with a multiplier of 0.2, which is also an unknown amount of Lumens (but very likely, very very low), by virtue of an unknown surface area for the fixture.
Meaning you're in fact lighting your scene with two very dim LEDs, likely not with what you thought you were after.
To ensure i had the flux i wanted, i extracted the shades and turned them into Vraylights, so to be able to specify the exact Lm (you lose the ability to texture the lights, but you may still tint them).

Next, and for both debugging, and illustrative purposes, i turned exposure off entirely.

Here is a result rendering with default for everything: lights and shaders' cutoffs, render settings (but for noise threshold at 0.01, quite high).
And overexposed crops of the bookshelf's interior which would not be sampled at all with your original scene, with a 0.005 and a 0.001 Noise Threshold respectively. Notice what actually was rendered, in the third crop:

So, i'd say overall you'd do well by yourself starting without any camera exposure, and with an override shader to ensure your lighting levels and light flux within the environment are feasible (and they will be, if you get light shapes and intensities right).
Once you're happy, move to shading, and only as a very finishing touch add in exposure to change what picture of the "real world" you'd like to take.

[^Lele^]

Micha The LWF literature is now very ample, albeit it has picked up a more refined lingo. You'll see scene-referred and display-referred mentions a bit everywhere by now (Sony's OCIO, ACES specs, you name it.).
V-Ray comes now, whichever the application, already in LWF, and yes, that does include the sRGB display button active in the VFB.
Anything else won't maintain the scene to display linearity.

[Micha]

^Lele^ At the moment I can use Vray 3.2 core at Rhino only, but i'm very curious how Vray 3.6 will handel the dark noise sampling in LWF mode. At the moment I got strong noise problems at a standard lit scene at dark shadowed areas and dark textures. Great to see that you find the solution for Dylan's scene.

[^Lele^]

^Lele^ At the moment I can use Vray 3.2 core at Rhino only, but i'm very curious how Vray 3.6 will handel the dark noise sampling in LWF mode. At the moment I got strong noise problems at a standard lit scene at dark shadowed areas and dark textures. Great to see that you find the solution for Dylan's scene.

3.3+ (on the max side) has the new sampler, same as the one shown above, and vastly superior to the pre-3.3
You should notice a good improvement across the board, but make sure you read the relevant posts about the new sampler, or you'll easily get lost (things change meaning!).

[dylan86.exe]

I've found out what it was, and my original hunch wasn't too far off (in that i thought it had to do with the colormapping), but boy was i not led into a merry chase! ^^
Let's go step by step, however:

I am not sure how "physical" your scene is: you have an omni light suspended mid-room casting sharp raytraced shadows.

Further, you're emitting twice, once from the spherical lights, and once, and in GI only, from the lamp shades. Make sure it's what you want, for i doubt you have a light in front of a light at home.
Using lightMtls in non-direct mode also tendentially leads to excessive work for poor results, but that's a different topic.

The third mistake was wityh your light intensities (more on this later), way too low, for which you overcompensated with the exposure settings.
In fact, if you turned exposure off, most of your scene would return pixel values below 0.001 (ie, always 0.000 for Value. see attached image).

Last but not least, while i miss the bitmaps, i can see that you're manhandling reflections and diffuse with non-physical falloff map modes.
It's really not ideal, as that map has serious age issues, including precision, besides the fact that you force light to bounce in very unorthodox ways (there is only Frensel in the real world. Varying, surely.).
Best you can do is stick (especially for stuff like plaster walls) to a GGX BRDF with glossy fresnel enabled.


It is, i am afraid, a limitation in current precision achievable with floating point numbers.
There is little than can be done to recover the loss of info at the edge of the precision through multiplication (what exposure does).

So, solution?
First, make sure your lights are of the correct size, and emissive intensity (for that, use IES profiles, or research the lm the light emits, and match it in the V-Ray lights with the provided units.)
You had it about correct for the spherical lights, at ~1500 Lm for a multiplier of 5.0 , but you have covered (ie. shadowed) them with the lightMaterial, with a multiplier of 0.2, which is also an unknown amount of Lumens (but very likely, very very low), by virtue of an unknown surface area for the fixture.
Meaning you're in fact lighting your scene with two very dim LEDs, likely not with what you thought you were after.
To ensure i had the flux i wanted, i extracted the shades and turned them into Vraylights, so to be able to specify the exact Lm (you lose the ability to texture the lights, but you may still tint them).

Next, and for both debugging, and illustrative purposes, i turned exposure off entirely.

Here is a result rendering with default for everything: lights and shaders' cutoffs, render settings (but for noise threshold at 0.01, quite high).
And overexposed crops of the bookshelf's interior which would not be sampled at all with your original scene, with a 0.005 and a 0.001 Noise Threshold respectively. Notice what actually was rendered, in the third crop:

So, i'd say overall you'd do well by yourself starting without any camera exposure, and with an override shader to ensure your lighting levels and light flux within the environment are feasible (and they will be, if you get light shapes and intensities right).
Once you're happy, move to shading, and only as a very finishing touch add in exposure to change what picture of the "real world" you'd like to take.

Incredible! I learnt a TON in you reply. Thanks so much LeLe!

[^Lele^]

You're welcome, but who is FreNSel?
I'm the typo monster, do fear me. ^^