GI surface details

[reck]

Turning this option on greatly increases render times, therefore it's important to understand two things.

1. When should you actually use this option, there is no point in turning it on and waiting longer for a scene to finish if it's going to have little to no effect.
2. What improvement will it make to a scene by turning it on, or in other words what does GI surface details actually do?

I have a partial answer as to when to use the setting and that is when the camera is low to ground, but not in all cases. What should we look for in order to determine if we should use this setting or not when we come to render?

Regards.

[rcallicotte]

It's when you want that ground detail.  I like using it, since the realness factor rises with its use.  But, I'm sure many observations have been made.

[reck]

It's when you want that ground detail.

But what does that mean? That description doesn't help me understand what difference it makes. What does it do to raise the realness factor and when is it prudent to use it or not?

I guess i'm going to have to bite the bullet and start rendering test scenes with surface detail on and off, it's just that this setting takes so long to render I was hoping someone could just explain it to me.

[bigben]

It's main use is for improving detail in areas of shadow where light is reflected from surround objects/sky/clouds etc....

e.g.
With GI: http://forums.planetside.co.uk/index.php?topic=1851.msg18019#msg18019
Without GI: http://forums.planetside.co.uk/index.php?topic=1851.msg18077#msg18077 (in the same thread, just scroll down)

It doesn't just affect the shadows, but that is where the effect is the most noticeable. In the example above, a different colour was used to tint the GI for surfaces and atmosphere, and as a result GI plays a much greater role in the final appearance of the image than just improving shadow detail. Notice the change in the colour of the sky at the horizon as you go from left to right.

GI produces much more realistic lighting effects than using just fill lights.

[reck]

Hi Ben,

Are you just talking about GI in general or specifically the GI surface details setting? It's the latter i'm interested in because I understand what GI does in general. From your description it sounds your talking about GI not the function of surface details.

Very nice Ben Nevis images BTW.

[JimB]

Great advice from Ben there. I'd also like to add that everything in nature has some kind of reflective value. Adding a reflective shader at the bottom of your shader stack can also greatly enhance the final look, if you're willing to add the rendering overhead (not always a big one either). They don't always need to be raytraced, it only needs to be a small amount, but it's worth making the reflections and specular highlights rougher to spread the effect more naturally. Works beautifully on snow especially, and can always be a child of a particular shader rather than overall.

[bigben]

Ah yes... I was talking about GI in general. I seem to recall that GI surface details is only useful if you are close to something (at least terrain, possibly objects?) Otherwise you won't see much difference. How close? Don't know. I haven't tested this setting yet.

[Oshyan]

I'm sure there was some previous discussion of this but I can't find it now. In any case I'm trying to get something definitive from Matt, but in short my understanding is that it increases the detail of GI calculations in areas of complex ground displacement. So for example Calico in your scene of fairly smooth rocks and water it would have little effect, though it still likely increases render time a great deal. Whereas in an image with a lot of Fake Stones or subtle displaced rock detail it would probably have a bigger effect. I believe the effect is rather subtle even when it is being fully utilized though, so I very seldom even attempt it.

- Oshyan

[reck]

Thank you Oshyan, that was the sort of response I was hoping for. The only info I could find by searching was that it should be used when close to the ground but with no extra details. I information regarding displacements was very handy.