Bug in SSS? (making candle, Octane 2)

[atnreg]

Hi!

I am desperately trying to make a realistic candle (once again) but I cannot get it to work

The problem is that there needs to be additional light source INSIDE the candle object to actually see the SSS effect, the light from flame object is not powerful enough. That would not be a problem if it worked as expected but at least I cannot get it to work.

The suspected bug is that there seems to be no way to create light source object inside another object that is SSS. The light object always creates 'shadow' in SSS object, see here:

I have tried to move the light source object, the shadow travels with it so it definitely is caused by the light source object.

If I put the light source object above the SSS object then it's outline is visible and creates other weird effects as well in render no matter what settings I tried (opacity 0, unseen check boxes in object etc.).

So please someone tell me what I am doing wrong and how can I make realistic candle with Octane SSS? I know the thread where SSS is explained but this is different problem, I made successful LED using ideas in that thread .

Thank you!

Antti

[3dreamstudios]

Not a huge SSS guy but in my experience Octane works best with real world actual things. Meaning it seems your faking the light source. A real candle would have just a sliver flame vertical from the wick. See if doing that would change the AFFECT of the light in the SSS material. Just a thought.

[juanjgon]

What happens if you dissolve the light object, using the LightWave dissolve feature in the object render options panel?

-Juanjo

[atnreg]

Good idea, unfortunately it does not help here

What happens if you dissolve the light object, using the LightWave dissolve feature in the object render options panel?

-Juanjo

[atnreg]

I prefer making as real world stuff as possible but here are the results, something must be wrong with Octane SSS or then I do something totally wrong

Here the light source is where there flame is:

Note how the top of the candle is DARK while it should be the brightest area!
Also note how the flame object is blocked by the light source even though Opacity=0

And here is a real Octane light (box, stretched):

Note the same dark area on top of the candle even though the light is radiating in all directions
Also note how the flame object is blocked by the light source even though Shape Opacity=0

The flame object cannot be used as light source because it would be way too bright at level that actually makes any SSS effect and the same dark area problem prevents from using it anyway.

Not a huge SSS guy but in my experience Octane works best with real world actual things. Meaning it seems your faking the light source. A real candle would have just a sliver flame vertical from the wick. See if doing that would change the AFFECT of the light in the SSS material. Just a thought.

[atnreg]

I did some more tests with simple cylinder and ball as light.

First, the cylinder is normal material, note the strange black area when the light object is close to cylinder
A bit longer distance, ok

Close to cylinder, strange black area

Then, when cylinder is SSS, again strange dark area on top. Note that the dark area goes away if scale is decreased but that results is way too translucent object for a candle so it is not an option.

Any ideas?

Antti

[atnreg]

More research shows that there is obvious and serious bug in Octane handling lights, not in SSS

Note the VERY strange 'shadow' from LIGHTING object! That is against all optical and natural laws!
The test scene is quite small (total height 4 cm, length 30 cm) but as Octane works best in real world scenes, it should definitely handle that.
And THIS is what ruins the candle making totally, the problem seems not to be in SSS after all as there is no SSS in this test.

The bug is even worse with Octane light, here using Linear light

Workaround is scaling the scene up by 10 but it makes some other things like material properties behave wrong so that is not any good solution.

Please fix this soon (if in plugin) or ask Octane crew to fix this soon if this happens in standalone as well (I cannot try as I know next to nothing about standalone).

Thanks

Antti

[juanjgon]

This problem can be related to the ray epsilon parameter in the kernel node. In a scene at the same scale that the one you are using, the default 100 um ray epsilon is fine, but if you put a big value (for example 20 mm), you can see in my scene the same artifacts that you have.

-Juanjo

[atnreg]

OF COURSE! I somehow didn't connect the ray epsilon to SSS in my mind but actually it changes the SSS behaviour A LOT! Even the light blocking the flame object is now gone

Thank you thank you thank you thank you thank you, Juanjo you are THE man!

I had ray epsilon at 10mm and that makes me think, is the ray epsilon the smallest detail that is needed to view correctly? Because in the test scene the 'border distance' of error is very close to 10mm, is that coincidence or does the ray epsilon work like that?

Antti

This problem can be related to the ray epsilon parameter in the kernel node. In a scene at the same scale that the one you are using, the default 100 um ray epsilon is fine, but if you put a big value (for example 20 mm), you can see in my scene the same artifacts that you have.

-Juanjo