View Full Version : Ambient Light mapping question ?

06 June 2011, 01:26 PM
Hi everyone,
I have a large outdoor scene which I want to render in the following way -

* One Ambient Occlusion pass
* One Directional Light for the Sun
* One Ambient Light for the illumination from the environment

I might add some other ShadowOnly and SpecularOnly lights if needed , but the general basic lighting setup is as above.

Now, I have a few questions about this ,

My Env_Sky geom is a hemisphere and has a SkyOnly texture on it. How do I use this texture correctly on the Ambient Light. Does an Ambient Light use a texture as if it were applied to a sphere and not a hemisphere ?
Also I have added a Sea geom underneath the sky , how do I include this colour information in the ambient light.

I would like to stay away from FG and GI as they will be too slow and may flicker as well. The default IBL from Maya MR with emit light turned on also is too slow.

Andrew Whitehurst says here ( that he used Angular Mapping for the Ambient Light , How do I do this in Maya with MR.

I have used an image from here ( and used Photoshop filter Polar Co-ordinates , Polar to Rectangle on it.

Heres an screenGrab (only SkyDome and ambientLight) (

Uploaded with (

06 June 2011, 06:20 PM
That tutorial is a bit old. These methods are not really modern now.

Are you interested specifically in how to do this using the tutorial, or just how to integrate an object?

06 June 2011, 04:46 AM
Thanks Bitter,
I just wanted a quick way to get ambient illumination on the objects. It seems IBL is the way to go in Maya MR, with the least hassle to setup. I am tinkering around to get the optimal settings. (

Uploaded with (

I made this with the same skyImage and the following settings,
-Only Emit Light turned on,no FG or GI
-visible to Environment turned off
-infinite on
-Quality U and V both set to 32
-Samples 64 and 16
-Value of 2 in ColorGain to boost 'Intensity' of the directional lights

If I increase the Quality anymore without increasing the samples , I get a spotty , noisy render. Its actually visible in the image above as well. But I will try increasing the samples for the final render. I am not going for realism and this look will work for me.

To include the sea and land colour info. from underneath I will just make a simple ramp with the sea/land colours and apply it to a layered texture which has the skyImage at the top and the fake sea ramp at the bottom.Then use this layered texture for the IBL.

I am also looking into Unified Sampling mentioned in this thread ( and see if it works.(just noticed the thread is yours,thanks for that one)
The render times are acceptable now. Any other optimizing tips you can give me would be great.

Also , I am just curious , what techniques are currently used. Are FG and GI really used in VFX production ? These days I only stick to animation tools in Maya and haven't played around much with rendering and stuff.

06 June 2011, 06:40 AM
VFX production will make use (mostly) of 2 techniques: Final Gathering (or whatever the render package calls it like an Irradiance Map) and a builtin IBL situation (Sky Dome)

The more current approach will be something like Builtin IBL. When you get set data it usually includes an IBL of some sort. This method is evolving but for now it works pretty well if you have an HDR.

Depending on your scene you can use the IBL without FG or other indirect lighting methods. Something like an interior would still need FG since IBL is direct lighting only.

IBL may be longer to render than FG but has a few advantages like automatic shadows, grain instead of splotches, and faster tuning.

You can look here: maya 2011 new ibl mode (

FG can flicker and be difficult to remove splotches with high dynamic hotspots but it is used fairly often. Just remember, in a VFX shot the chance of you seeing these errors is pretty remote. So don't spend too much time over-tuning a parameter until it takes forever to render. Grain and the like won't be noticed and you should judge a quality level in motion with a few frames. In fact, in post we usually add some grain back based on the original plates.

Unified + Builtin IBL work well together because tuning can be done with 2 "Quality" knobs and nothing else. Or you can rely on the Unified Quality knob for everything if you are ok with sacrificing a little efficiency in favor of simplicity.

06 June 2011, 09:23 AM
Thanks a lot for all the help Bitter.

I tried the Raytraced Shadows from IBL and it seems to be good enough. (

Uploaded with (

With FG on , the render looks pretty sweet. (

Uploaded with (

I also did a test with motion (good advice) and see no flicker or noticeable noise. MR FG seems to have improved tremendously. I remember turning on Raytrace shadows or FG and waiting for minimum 30mins for the render to finish on a simple scene , ofcourse this was a few years back.
I could see some kind of at least one bounce colour bleeding going on in fully animated movies for a while but was wondering if FG was also used in VFX or not.

I dont think I am gonna bother with Occlusion. Only FG with IBL raytraced shadows is great and rendertimes are acceptable.
I will look into more MR settings and options as I go along , but for now I can move on. Thanks again.

06 June 2011, 09:29 AM
Usually combining options in mental ray are designed to work better together. Most of us expect that combining them would increase overall render time for a similar quality but it's not always true.

In this case the IBL provides the first direct lighting and FG fills in the rest. Since the IBL is importance sampled and low-noise, FG can benefit from that precision and render with fewer problems. FG+IBL will generate enough detail that you can forego occlusion in a lot of cases.

With the exception of Final Gathering, most anything sort of brute force like IBL or Occlusion can be tuned using the Unified controls as well.

Would like to see some of this as it progresses. :)

06 June 2011, 12:31 PM
Cool , I am working on some animations for my reel and wanted to give the creature animations some kind of a context. Hence the simplistic environment work. Its just good enough to suggest scale and atmosphere. I am not adding any textures but trying to get the colours and lighting right and hopefully the animation will show through.

It might take me a while but I will upload my finished work here on cgtalk to get some feedback for sure.

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06 June 2011, 12:31 PM
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