Ambient Occlusion Node Tutorial

Author : Paul Kinnane

You can post any questions you have on this tutorial to this thread.

This tutorial explains how to use the Ambient Occlusion node in the Poser 6 & 7 Material Room. It does not cover light based ambient occlusion. This tutorial is not relevant for Poser 5.

NOTE: Rendering with Ambient Occlusion (AO) node on materials increases render time. But if you want realism and quality renders, it’s an invaluable tool that is well worth the additional render time.

Why used the AO Node? Because it allows you to add very fine detailed shadows to your renders that would not be possible using depth mapped and ray traced shadows. AO nodes are particularly useful for making objects appear to be touching – for example, making clothing look like they actually ON the person wearing it, or making a hand look like it’s actually resting on a table.

The Basics

Before covering the applications of the AO node, let’s look at what the node looks like, and how to plug it in. ….

The image above taken from the Material Room shows the menu options to use to create an AO node. The AO Node itself contains the following parameters:

- Samples : The number of ray samples. For normal rendering, 2-3 samples seems fine. The more samples, the longer the render time. If you use large MaxDist figures (> 20 inch), you may need to increase the Samples from 3 to 4 or 5.

- MaxDist : The maximum distance a will ray travel to give an AO effect. This parameter effectively controls the darkness and intensity of the AO effect

- RayBias : The smallest amount a ray must travel in order to result in AO. This should be as low as possible, without causing rendering artifacts

- Strength : This parameter appears to have no effect!

Plugging in the AO node

You can (and initially should) use the Set Up Ambient Occlusion button in the material room to setup AO on the material you have selected. Pressing the button will setup something like this….

You can see that the AO node is creating AO effects by controlling the diffuse and specular values. Of course, if you have anything plugged into the Alt_Diffuse or Alt_Specular, you will need to setup the nodes by hand, and they should look like this….

The ApplyAODiffuse and ApplyAOSpecular are color_math nodes.

Note : There is a python script available (the OcclusionMaster for PC and Mac) which can assist you with plugging in all these nodes .

Recommended Initial Settings

These settings are for when your Poser preferences have the display units set to INCHES.

- Eyewhite – max dist = 1, RayBias = 0.01

- Skin – max dist = 3, RayBias = 0.4 (if the skin uses a displacement map, or the joints are severely bent, you will need to increase this to 0.5-0.6 to get rid of artifacts)

- Clothing, wall, etc – max dist 5-50, RayBias = 0.5

Rendering with the AO node

Firstly, you MUST have ray-tracing on in your render settings (2 bounces is fine), and be using the FireFly renderer.

Shadows : You can use the AO in place of other scene shadowing, or in conjunction with traditional light shadowing or AO. For example, if you are doing a portrait render, you can switch off shadows, and have AO nodes on the eyewhite, nostrils and lips to get realistic shadowing. Or you can switch on shadows for one or more of the lights, and have them working together with the AO nodes.

Hair : It is not recommended to use AO nodes on hair. Also, I suggest unchecking the Visible in Ray Tracing check-box for any hair figures or props in the scene, since including hair in AO calculations takes a very long time. Use traditional depth mapped shadows for hair shadowing.

Light based AO : You can use light based AO together with AO nodes on materials, however it is recommended that you make the RayBias of the light AO approximately the same of the largest MaxDist you are using on an AO node on a material. This should ensure that the light and materials Ambient Occlusion doesn’t double-up.

The AO node in action

OK, lets see what all the fuss is about.

For these examples, I’ve used GI Jill (for V3), since she has some clothing and props that demonstrate AO in action. Also, I’ve switched off all light based shadowing, to demonstrate the AO node functionality more effectively.

In the above example, an AO node was attached to GI Jill’s SkinTorso material using the method described above in Pluggin in the AO node. You can see the effect is stunning. The version without AO lacks depth, and it doesn’t look like the bikini or dogtags are touching her body. The render on the right, with the AO node on her SkinTorso has added AO shadowing between the bikini and dogtags and her skin – creating a much more realistic scene. In this case the AO looks just a touch strong, so a MaxDist of 2 might be better then 3. Also, you can see there is no AO at the back right of the dogtag strap – since that falls within the RayBias of 0.4 inches, so reducing that value would help too.

Let’s see how AO nodes can help with a prop….

In the above example, I added an AO node to GI Jill’s Cap material, which you can see has very effectively added depth to the Cap by adding a small shadow to the seams.

You can do the same trick on floor props, as can be seen below, where without the AO node on the floor ClothPlane, there are no shadows, which makes GI Jill look likes she’s suspended in the air. There is also an AO on her SkinLeg material to get the shadow from the top of her boots onto her shin.

In the above example you can see that the shadow on the floor is not completely even. This is because I’ve used a large MaxLen, but kept the number of samples at 3. Increasing the samples to 4 or 5 would fix this.

Finally, lets look at AO node applications in the face….

In this example, I’ve used an AO node on GI Jill’s Lips material and her left and right eyewhite materials. The lip effect is obvious – the AO node gets rid of the harsh light to dark border between her lips. The eyewhite has been less effective in this example – however you can see that it has added a slight shadowing between the eyewhite and her eyelids. This technique works on DAZ Unimesh figures, but cannot be used on Jessi or James, since they have eye covering geometry which adversely effects the AO node. Also, you cannot add an AO node to the Unimesh iris materials, since the cornea material covering the iris effects the AO effect.

That’s it! Happy rendering with the AO node.