Lighting - I'm confused. Tweet

[gordonrobb]

Managed to get it to look better by tweaking ISO to 400 and Gamma to about 1.4. No hope with AO though.

Feel free to try.

[PAQUITO]

You are right, using AO you must have an environment as a fill light. What I do for this kind of scenes is setting up the emitters, then powering up the environment until it fills the black areas properly. It´s harder to get a realistic image, but it´s possible. With the diffuse mode is way easier. You are trying to light a big scene with little emitters, so you must have very bright emitters, or else raise the gamma.

First image: Diffuse mode, 3 bounces. Gamma 2.2
Second image: AO shader with HDRI env and gamma 1. The textures are crappy since they are just placeholders.

[UnCommonGrafx]

The hdri route seems to work rather well.
Good lesson.

[gordonrobb]

Paqiito: as you can see in my last post I managed to get it looking ok by tweaking ISO and Gamma. What I don't understand is, if this is a physically accurate model, why does having any kind of external lighting (HDR, texture or daylight) make any kind of difference at all. This space is enclosed, how is the light getting in? And this question the leads me to, how do I know which is the physically accurate method to get internal scenes (with no external light sorce) lit and showing realistically. In my bedroom at night, I can piu on a night ligh (tiny light source) and see all of the room lit slightly, for example.

[juanjgon]

AO is not physical accurate GI solution. It uses environment lighting to shade the scene, not a real multibounce GI diffuse model (AFAIK).

Only Diffuse mode in the directLighting or the Pathtracing/PMC kernels allow real GI multibounce lighting.

-Juanjo

[UnCommonGrafx]

I played with your scene and was able to get something usable by raising the exposure.

Your example question is why I did it. I don't get the hdri in a closed room, though.
That light at night, is it that you've just woken up and can see the whole room, for example? Your exposure setting is about at 20. Turn on one light; this changes your aperture and the exposure. Then turn off the light. Eyes will take a moment to get back to the right exposure and aperture.

I like the photographic lean of Octane.

In my bedroom at night, I can piu on a night ligh (tiny light source) and see all of the room lit slightly, for example.

[PAQUITO]

What you are seeing in a dark night with a tiny light is not what your eye is seeing, but what your brain is interpreting from the poor information the eye is providing. A photographical camera shows exactly what the lens is "seeing". That´s why you can´t compare the two things.

In other hand, the AO shader doesn´t calculate rebounds, it´s only a shader. It fakes bouncing light using the environment, even in a closed space, you can set up an environment, and the shader will distribute it through every little corner of the scene, no matter how complex it is. That´s why the AO kernel is so fast, because it doesn´t calculate things, it fakes it, so, yes, it´s not a correctly physical approach in no way.

[gordonrobb]

Thanks guess. In hindsight, I had remembered that the Direct Lighting Kernal was not unbiased, but had missed that AO wasn't true GI. So for internal, trying for accuracy I should be using Diffuse, or Pathtracing/PMC kernal.

I am aslo happy that I need to tweak the f-stop and ISO settings. A little less happy with exposure as I don't like the effect it has, and same with Gamma, although a small adjustment of gamma does work wonders. The image below is f1.8 ISO 800 and gamma of 1.2 with Agfacolour presets.

I'm happy with the result. I'm even getting my head round the Spec and Roughness settings. LIghtwave guys will know that Spec/Gloss worked a little differnt. So Got this sussed, I'll work on the modelling of this big scifi door later, but thanks for your help everybody peeps.