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Ambient Occlusion In Reverse

For use with Poser 6 or 7

One of the significant features of recent versions of Poser is the ability to use Ambient Occlusion, the natural property of objects to obstruct ambient light, shading nearby surfaces. In this tutorial we'll walk through the process of using an Ambient Occlusion node in the Poser 6 Material Room to produce the opposite effect...The current Poser Material Room is both easier to use (thanks to the Simple interface) and even more powerful than its Poser 5 counterpart. One of the significant features of Poser 6 and 7 is the ability to use Ambient Occlusion, the natural property of objects to obstruct ambient light, shading nearby surfaces. Ambient Occlusion can add a striking degree of realism to your Poser renders- but a little mathematical trickery with an ambient-occlusion shader node in the Material Room can produce some even more dramatic effects. In this tutorial we'll walk through the process of using an Ambient Occlusion node in the Poser 6 Material Room to produce procedural glowing surfaces- this lets you create effects ranging from lava glowing in cracks-

- to barbecue coals ready to cook in a grill-

- and beyond. Radioactive fuel rods, alien artifacts, magic items, you name it, any time you have surfaces in close proximity, you can use this effect to make them glow.

So, how does it work? Simple. First, we'll bring in a prop to which we want to add a glow. I've used this barbecue grill and coals that I modeled in Shade. I'll select the coals and open up the Material Room, then click the Advanced tab.

First, I'll choose the proper material group for the coals, then I'll create a Color_Math node (New Node>Math>color_math) attached to the Diffuse_Color channel of the PoserSurface. For the first color, I'll pick an ashy grey; for the second, a bright, saturated orange. I'll leave the Math_Argument set on Add. Now, I'll create a Math_Function node (New node>Math>math_functions) and set the Math_Argument to Subtract. I'll attach the output of that node to the Value 2 input of the Color_Math node (the orange channel.) In that math function node, I'll set both values to 1.5 (these can be adjusted later to give different effects.) Now, I'll create an Ambient Occlusion node (New node>Lighting>Ray Trace>ambient_occlusion) and connect its output to the inputs for Value 2 of the Math_Function node and Value 1 of the Color_Math node (the grey channel.) After adjusting the parameters of the ambient occlusion node (I'll set the MaxDist value to 3.5, the RayBias to 0.025 and the Strength to 2.5), I'll connect the Color_Math node to the Specular_Color and Ambient_Color channels as well, and adjust the base colors for those channels to varying shades of gray (the Ambient_Color channel is the essential element of this trick.) Since barbecue coals are rough, I'll also attach a Noise node to the Bump channel. The resulting setup looks like this-

Now it's time to set the Firefly parameters and adjust the lights for maximum effect. In the Render Settings dialog, be sure to use a setting that has ray-tracing turned on with at least two ray-trace bounces; you may also want to turn off shadow-casting, as this can literally overshadow the glow effect. There's another way to achieve the same result, which I'll use here- just use the Parameters and Properties palette to turn off shadows for all but one of the lights in your scene. Now, with that all set, we can render the scene-

This looks pretty good, but the real fun starts when we darken the scene up by lighting from underneath- or just deleting two lights and turning the last one down very low (turning off shadow casting on this light will also help); rendering in low light now gives us this-

Notice the dramatic glowing effect- this is the Ambient channel at work. You might need to adjust the values in the Math_Function node and play around with the values for the Ambient, Diffuse and Specular colors- in particular, turning up the Ambient value will increase the effect- but this should get you off to a glowing start.

Thanks to Larry Weinberg and Jack Walther for figuring out the math!