How To Get Identical Results with Dome Light and GI Environment

[Jorq1H]

I have to admit that the more I think of it the more the terms direct and indirect light are too nebulous. For me as an artist, I read direct light as light coming from the light source and hitting a surface (whether that light source is a tranditional cg light or the sun painted on an hdri), and indirect light means light that comes from a surface and hits another surface (or bounce light). From what I remember back in the old Brazil days, the reason a skylight (or in vray, the GI Environment) is considered indirect light is because the light is "bouncing" off the environment and then striking the objects in your scene. But as an artist, an hdri, while technically an environment, isn't an object and so should be considered a direct light source and not a bounce light source.

My brain hurts

- Neil

Totally agreeing with you. The interchangeable nature of this software's terminology can get really confusing. I'm also seeing only indirect light when casting IBL from VrayMeshLights. I have no idea why it's not producing direct light, even though Store With Irradiance is turned off and the GI override is disabled. An issue for another time, I guess.

[Dariusz Makowski (Dadal)]

Totally agreeing with you. The interchangeable nature of this software's terminology can get really confusing. I'm also seeing only indirect light when casting IBL from VrayMeshLights. I have no idea why it's not producing direct light, even though Store With Irradiance is turned off and the GI override is disabled. An issue for another time, I guess.

Can you show me an example of this? This sound incorrect to me..

Well, I get the lack of specular reflections, since it doesn't provide anything to reflect. And I get the blotchiness since the samples on the vray light are kind of low. But I hadn't noticed in my tests the shadow sharpness issue. Again, will do some test renders tonight and see if I can replicate them.

- Neil

The blotchiness comes from GI not from light. Light is raytraced and GI is well it depends which solution u use...

[soulburn3d]

So it must be really hdri dependent. Attached are two different hdris (one is outside, the other inside with light coming through windows). Note they both look pretty identical in terms of shadow sharpness (although the environment one tends to be more noisy) So that's why they seem the same to me, must just be the particular hdris I'm using.



- Neil

[Jorq1H]

So it must be really hdri dependent. Attached are two different hdris (one is outside, the other inside with light coming through windows). Note they both look pretty identical in terms of shadow sharpness (although the environment one tends to be more noisy) So that's why they seem the same to me, must just be the particular hdris I'm using.

[ATTACH=CONFIG]18823[/ATTACH]

- Neil

I might be mistaken, but it looks to me like both those hdrs have relatively large light sources. I think the difference between dome/GI-override is more pronounced when using hdr's with way smaller sources, e.g. the sun. In my example the sun spot was only a few pixels wide, and that seems to be a problem for the GI engine when it's not cast as primary rays (resulting in lots of noise and splotchiness). I'll have to continue testing with more samples to get any wiser, I suppose.

[Dariusz Makowski (Dadal)]

Heya

Yes those examples are very close to each other. Both of these approaches do should look similar at they highest settings with the difference of lack of secular component in Override case. The smoothness and noise that dome produces is related to quality of IBL texture. If its a night shot with lots of smart light sources then you need a lot more samples then for example a sunny desert with 1 sun as light source. You always have to add more samples to the dome in order to clean up the noise. Its really up to you how you use. But general practice in industry is that you use dome for direct light/specular and overrides only in special cases. There are drawbacks to GI based lighting solution.

1. It can back fire on render times
2. Relative to GI settigns which can be very high for certain scenarios (as well as Dome approach)
3. Your shadows tend to be more blurry and less accurate, you can see it in ur example.

Try rendering something bigger, a viz/interior and so on you will see how much longer it might take than direct Dome.

Try doing some compelx tests, this teapot might be misleading you..

[soulburn3d]

I might be mistaken, but it looks to me like both those hdrs have relatively large light sources. I think the difference between dome/GI-override is more pronounced when using hdr's with way smaller sources, e.g. the sun. In my example the sun spot was only a few pixels wide, and that seems to be a problem for the GI engine when it's not cast as primary rays (resulting in lots of noise and splotchiness). I'll have to continue testing with more samples to get any wiser, I suppose.

Yes, both of these have light sources certainly larger than a few pixels across, so ya, I guess that's reason I didn't see much of a difference. But its good to know the difference is there if I use a more focused hdri. I'm going to stick with dome lights from now on anyways for an entirely different reason, I need to be able to move light rigs between files, and so an actual light object can be easily merged from a different scene. Anyways, thanks for the info!

- Neil

[raymarcher]

Here is my cheat sheet for dome lights:

General:
-acts like the equivalent of a spherical placement of like 1000 area lights
-uses adaptive sampling to sample dome light texture
-allows lighting a scene with an image without using global illumination
-is not meant to be used as a light portal
-was created for situations where good indirect sky shadows were needed with fast smooth GI
-the dome light contribution is stored in the lighting render element instead of the GI render element
-dome light noisier, environment skylight splotchy

Uniform sampling:
-classic environment skylight
-uses uniform sampling
-Vray samples the HDRI map uniformly wasting samples in low contrast and low contribution areas
-this results in high render settings to obtain quality
-no more blurry HDRI maps needed to avoid splotches

Adaptive sampling:
-dome light
-uses adaptive rays or importance sampling
-Vray samples the HDRI map after it was analysed levelling samples in important areas
-this results in lower render settings to obtain better lighting, shadows and caustics...
-even very small bright regions like the sun can be sampled accurately with very few samples

Specular:
-since it is a direct light it produces specular
-are based on the used map

Reflections:
-is more efficient when dealing with glossy reflections

Shadows:
-dome light area light shadows are slower but more detailed then GI generated shadows
-dome light area light shadows are faster if GI shadows are setup to have the same amount of detail shadows


Usage

Classic environment skylight GI
-acts as indirect light
-has only indirect rays
-creates indirect GI shadows
-quality lighting depends on GI settings
-needs high irradiance map settings for details

Dome light non GI:
-acts as direct light
-has only direct rays
-creates indirect ray traced area shadows from HDRI
-quality lighting depends on dome light settings (subdivisions)
-has high detail shadows but no bouncing

Dome light GI:
-acts both as direct and indirect light
-has both direct and indirect rays
-creates direct area shadows and indirect GI shadows
-quality lighting depends on dome light settings (subdivisions) and GI settings
-needs lower irradiance map settings for details, dome light does detailed ray traced area shadows

Dome light GI store with irradiance map:
-acts as indirect light
-has only indirect rays
-creates indirect GI shadows
-quality lighting depends on GI settings

Disadvantages when stored with irradiance map:
-acts like classic environment skylight when you choose full spherical
-has more parameters to manage like dome light subdivisions
-longer render time
-no indirect speculars
-loss of advantage detailed ray trace shadows