Physically inacurrate light distribution in Octane

[SSmolak]

This too dark area under "balconies" is not acceptable in modern professional architectural visualizations. Sorry to say.

Increasing ground brightness is not the way because in most of real scenarios, ground is always darker.

But there are three workarounds to make it looks better in Octane - black body emission, additional fake ground invisible to camera with emission and AOV Diffuse Indirect mix with triplanar y- on surfaces. Anyway it should looks better by default.

isn't this most likely "solved" with tone mapping?

Nope because "issue" is only on some parts. It can be done in Photoshop with dodge brush using 32bit image.

I will make new Corona scene with proper Corona material nodes. The last one was not accurate. Also to make sky the same I will use HDRI image instead of build-in generated skies.

[SSmolak]

There are more accurate and near the same scenes. Corona has slight different representation of Hosek-Wilkie Sky mainly color. Left Corona, right Octane.

I think that Octane do it better, more detailed shadowing. Corona is slighty more washed up so I add 1.2 gamma to Octane to make it looks near the same.

I noticed only now that Roughtness doesn't work in Universal Material like it is in Diffuse Material. It works only for specular, metallic or transparent materials. Is that intented ?
Materials like wall looks better in Diffuse Material type and with little roughtness.

[SSmolak]

Octane Standalone scene included.

Please let me know if this file works fine in Standalone because I have black screen on render output. I don't know that this is Standalone issue or something wrong while exporting from C4D.

[SSmolak]

Thank you for info. Yes it works fine now. Here is updated file.

[noldo]

Try this.
You can boost the "fill light" effect raising the emission power.

[SSmolak]

Probably you sent wrong file. There is no Emission anywhere on materials and light. I had temporary scene with fake unvisible ground and emission turned on that works great for additional fill light.

[SSmolak]

Thank you very much Elsksa for that ! It looks very interesting. I will check this more deeply soon.

[SSmolak]

Please see ambient light scenario compared to real photo. Octane completely ignore indirect light bounce to polygons that are not directly exposed to ambient sky. I have the same colors and the same ground brightness as in real photo.

There is no light bounce to ceiling from floor and adjected walls.

It even partially ignore reflections :

Please don't tell me that this is physically accurate.

To make the same brightness in Octane there is need to increase ground brightness but in real scene ground isn't that bright - there is more grass around than pavement. Also there is need to fully increase diffuse roughness that works only for Diffuse material ( problem described here : viewtopic.php?f=23&t=80314&p=414925#p414925 )

Increasing sky brightness do nothing for polygons oriented directly to ground. There is no light bounced from walls to them - only from ground that is very strange...

more references : https://www.shutterstock.com/pl/search/ ... chitecture

[SSmolak]

I found solution :

The problem was Octane Hosek&Wilkie implementation but not only.

1. Hosek&Wilkie implementation is totally not suitable for creating ambient, cloudy lighting because even without sunlight increasing turbidity create very large, bright halo on the sky. This halo cause shadowing even if it is placed near sky zenith - it create shadow under balconies. The best is to use cloudy HDR maps or old Octane daylight model where we can avoid this turbidity halo and make more uniform lighting.

2. Using diffuse, color, albedo ( no matter what it's called ) on walls should be avoid or with little percentage only. For little irregularity, bumps the best is to use normal maps. Octane do it right for simulate little bumps, cracks etc with natural darkening without the need of use albedo maps. AO maps should be not used at all - they are creating fake shadow effect that darked whole surface. Use albedo only for color changes or dirts.

3. There is need to use roughness on diffusion too. Octane use it only in Diffuse Material. For all other materials roughness is used only for specularity, reflections... To make more soft light distribution on corners there is need to use Diffuse Material with roughness like 30-75% and if you want specularity - use Specular Layer.

After that we have even more bright polygons in corners or under balconies than in reality where in typical situation main wall has 45% RGB brightness, polygons under 30% and ground average 40%.

[SSmolak]

I decided to wake up this thread because after year of making architectural viz's, testing, comparing renderings with other engines and self investigation, photos I'm 100% sure that Octane has serious issue in the terms of light distribution in not only dark areas but especially with polygons that are not directly exposed to direct light !

This is why most of the people use Corona and VRay for such type of renderings.

Within the time I saw people that asked the same, some days ago for example : the same interior scene in Corona and Octane : https://www.facebook.com/groups/OctaneR ... 3274330068

Problem is with :

1. When in some areas light power is decreased gamma fallow for materials in Octane is decreased too much - it create too much darkness in dark area. Also color of material distribution to other material is decreased too. It create somewhat flat areas especially in interiors where light from brown wood floor should be bounced more.

2. Octane doesn't take in mind that light bounced from bright wall to another bright wall should increase its power to make wall that it is oriented 90 degrees to them should receive more light power that from outside environment - like these walls above balconies that are not directly exposed to direct and indirect light from sky or Sun.

For making exterior ambient light like cloudy sky sometimes best is to use Direct Lighting with Ambient Occlusion mode especially in dense, tight areas ! This is nonsense :

Example of dark area but should be more bright because of 80% bright ground where light should be bounced to up :

Underexposed parts :

O1.jpg (24.79 KiB) Viewed 2528 times

O2.jpg (18.63 KiB) Viewed 2528 times

Real photo, ambient, cloudy sky. Balconies obstructed by trees. Pure white even on walls under - impossible to make in Octane :