White spots with vraylight+refractions

[Dragony]

Hi.

I am completely new to vray and played around with it a little bit. Nothing special... created a teapot on a plane, created a vraylight above it and tried to make the teapot transparent. So vraymtl applied to it, reflection set to black, refraction set to white, glossiness 1.0, IOR 1.3.

But then I see some white spots on the teapot... They look very ugly and unnatural. I played around 2 hours now and found out that its completely dependend on the combination witht the vraylight and the refractions... If I take another light, it works. If I disable refractions, it works.

I found another post about white dots and the answer was that the light was way too bright. Well, my light has 3000 units and it enlightens the scene in a good way. If I lower it to 10, the scene is completely dark... except the white dots, which are still white.... Only if I lower the value below 1, they become gray and 0 makes them black.

Can anyone help me?

[voltron7]

can you post an image?

[simmsimaging]

Try disabling GI caustics and see if that clears it up. I have had problem with white dots that I could only eliminate by turning of (in my case) reflective GI caustics.

b

[Dragony]

I don't use Caustics there. The checkbox at "Caustics on" is not checked, so I assume they are disabled.

I attached 2 images. First one is the way "it looks good" (multiplier 300) and the second one is just multiplier 10, which causes the scene to be nearly black.... Just the darn spots are still there and white... Doesnt really look nice...

[zeronove]

Try to check clamp and sub pixel mapping in color mapping rollout and see what happens

[Dragony]

sub-pixel mapping did not change anything. Clamping changed the look a bit (I think a FEW less white dots), but it does not solve the problem. I attached the scene and replaced the floor with a checker. It is a direct download, so no hassle.

vray_problem_with_teapot.zip

[simmsimaging]

It looks like an over-exposure thing combined with a lighting problem. You can't "directly" light glass the way you are trying, at least not without pumping a ton of light into the scene which makes the specular reflections way too hot. If you set up the lighting better (add more lights that bring out the shape, light the background up a bit more etc.) you can bring the power down and they won't blow out as much.

b

[Dragony]

But why has the dark image also white spots? And why does it work if I use a different light? For example a Omni with area shadows?

[simmsimaging]

I'm not sure why it would be better with an omni.

b

[Dragony]

WHY I don't know. But it is. I still wonder why this phenomenon seems to be so unknown to anyone? Is this something never being used?

I attached both images. First one with vraylight, the second one I placed an omni light with area shadows at the exact location. I did not invest much time to make the images exactly identically, but I think its clear what I mean.

[simmsimaging]

It seems consistent with what I said: the omni is not creating any direct reflections so you are not getting blown out reflections of the light source. You can try turning off reflections for the Vraylight - that should get rid of the problem, but you'll need to add something else back in to create some sparkle.

I still think this is a lighting problem, not a glitch.

b

[Dragony]

Hmmm can you explain me the following images?

First image: vraylight with decay on. multiplier 40
Second image: vraylight with decay OFF. multiplier .8 to maintain light level "as good as possible"

For me it seems there is a bug in the calculation of the refraction at some point, where vray calculates some rays without using the decay algorithm.
this also explains my images some postings before, where you basically have a completely black image with a few white dots.

[simmsimaging]

That is not an apples to apples comparison. The second one has controlled highlights because the multiplier is very low. You have an artificial sense of illumination levels because the decay is off. Decay will make the cast illumination drop off, giving you your very dark render, or an artificially evenly lit background in the case of your second tests, but it does not affect the brightness of direct reflections of the light source, which is why the reflected vray light is still blown out in your first tests.

It's still the same problem with your lighting setup.

b

[Dragony]

Hmmm I see.... but I set the light source to be invisible? How could it be visible in a direct reflection?

[simmsimaging]

not invisible - toggle off "affect reflections"

b