View Full Version : Help with light bounces for this scene

07 July 2010, 02:15 PM
Me again with another MR question: what would be the best way to increase indirect illumination on the front walls of the house here, under the far gate and the other dark areas? Basically to increase what you can see in the shadows in the scene to the point it'd be like an overcast day. The shadows are way too dark.

It's currently using IBL with an HDRI and FG with 3 bounces.

(ignore the sky and the halo btw, that was just me mucking round with the premultiply option)

07 July 2010, 02:45 PM
If there are only some isolated areas of the scene where you need to increase lighting, in my opinion the best way is to add additional lights in those areas, rather than trying to play with the GI or FG settings. Sometimes a realistic result may simply not be pleasing to look at, so it`s perfectly acceptable to cheat a little.

For the premultiply option, it only works correctly in mental ray if you have a black background. As soon as the background is anything else other than black, then you get those white outlines, which are junk. It works fine in maya software though.

07 July 2010, 05:54 PM
hey there..
Im not sure what shader you are using, but if you are using the mia_material there is an option in the shader, under the indirect illumination tab that allows you to change the amount of FG contribution on a per shader basis. Upping this value should lighten all the areas in the scene that have the shader applied, and that brightness should also lighten your shadows..

hope it helps

07 July 2010, 06:16 PM
If you're looking for an overall light gain, you can increase the Scale of your Final Gather primaries beyond 1 for a quick solution. This may wash out other areas though, but it's something to keep in mind.

07 July 2010, 10:20 AM
Thanks for the suggestions. Bear in mind I have no GI active...would that be a good or bad direction to head in for this issue?

07 July 2010, 11:30 AM
Bad. FG is good enough for those exterior scenes.

GI is interesting when you are rendering an interior since the light bounces on the walls, ceilings, couch, etc... In fact, I never use GI (in mental ray of course, I did use it in finalRender or Vray since it's really simple to setup and fast to render). I prefer to use FG and arealights if I want to increase the brightness in some places, to fake the bounce of direct lights, etc...

07 July 2010, 03:34 PM
I agree with Dot. GI is inefficient and unnecessary for most outdoor scenes, and is a very specific type of lighting solution. It works best with lots of shinies, glass and metal and walls and floors which are all at least slightly reflective or refractive. In a wide, open scene such as this, the photons would have to be set very high (long render times) to make any impact, and then you'll likely get lots of splotchies. FG by itself is usually just fine for outdoor scenes.

CGTalk Moderation
07 July 2010, 03:34 PM
This thread has been automatically closed as it remained inactive for 12 months. If you wish to continue the discussion, please create a new thread in the appropriate forum.