Physically inacurrate light distribution in Octane

[SSmolak]

I noticed that Octane has trouble in specific situation with light distribution between polygons that are placed on some large distance like > 5meters. It is much more noticeable on exterior architectural scenarios where skyligh should be bounced from ground and travel up to light surfaces that are not directly exposed to direct light. Under balconies or deeply corners, small tunnels we have light leaking - they are underlighting. Indirect light has problem to reach to these areas on larger distance.

This is why architectural oriented renderers like Corona or VRay do it better by default.

After some tests I found solution but I don't know that this is not a cheating, dirty solution. There is need to turn on Blackbody Emission and everything looks as in Corona or even better because we have control for emmission power. But other renderers magically do it with using only surface diffusion parameter.

I of course had albedo at max and cranked up sky power. Path Tracing diffuse depth on max.

Bad thing to use Emission is that while using dusk or night sky lighting scenarios we must turn it off or reduce because walls looks unrealistic. Two different materials for two different light scenarios ? Very bad. Also as I know Blackbody Emission should be used for surfaces that generate light.

Also this is why I thing that Octane architectural viz looks worse that these done on Corona or Vray - because people should turn on Emission to compensate underlighting.

First image is with albedo only on surface, next one is with Blackbody Emission on.

[SSmolak]

with adding a little specularity thanks to Universl Material it looks even more sexy than in Corona. It should be described in manual that BlackBody is not only for materials that emit light.

[SSmolak]

Unfortunately using blackbody emission we lose those small eye catching light shadows. More emission=less shadowing and more "milky" ambient like diffusion.

[SSmolak]

I think that this is simple to do for Octane developers to make switch in material settings to get more indirect light in such situations but little desaturated too. After that arch viz people can make really good materials. Switch like "Indirect Light compensation".

This not only improve light distribution in specific situation but will bring Octane closer to arch viz renderers where they have it by default.

[noldo]

Interesting!

[noldo]

I've made a few attempts based on your assumptions. You could have a result similar to what you are looking for by setting a spherical geometry primitive by mapping it to the diffuse channel with the same hdri as the lighting (removing the sun, if any) and closing the scene in this sphere. Obviously the sphere, conveyed with an object layer map, must be disabled from the camera and the shadows. This causes the rays hitting the sphere to flow back into the scene, causing fuller lighting in the shadows.

[SSmolak]

Noldo - sounds very interesting. I will try.
I'm trying also with invisible big area light on the ground and it looks very well but probably it is not as good in the terms of performance.
Next one trick is to use triplanar projection to add more brightness to Y- polygons.

But all of them are only trick that are not physically corrected. The best should be natvie option to increase indirect light brightness included in material settings. There is really visible differences how the same object looks in another renderer.

[SSmolak]

You could have a result similar to what you are looking for by setting a spherical geometry primitive by mapping it to the diffuse channel with the same hdri as the lighting (removing the sun, if any) and closing the scene in this sphere. Obviously the sphere, conveyed with an object layer map, must be disabled from the camera and the shadows.

I tried your solution but what about ground ? Lower side of the sphere is obstructed by ground. I know how to disable such ground from lighting in CPU renderers but not in Octane

[abstrax]

Without an example scene there isn't much we can do/say here as visual light distribution depends a lot on the materials, the kernel settings, the lighting+environment of your scene and even the imager settings. -> Please send us or post an example scene so we can have a look.

[SSmolak]

Simple scene attached.
I noticed that this light leaking effect under polygons directed to the ground is more noticeable when textures are added to the materials.
I know that this strongly depends on lighting condition but anyway Octane looks more darker in that situation compared to others. Metallic material for example generate near totally black polygons if they are directed to the ground which is at some distance to them.

Changing rendering type do nothing in this situation.