bagginsbill opened this issue on Oct 25, 2007 · 273 posts
bagginsbill posted Thu, 25 October 2007 at 8:54 AM
When showing something on a surface or floor, a lot of realism is lost because we don't get nice soft "contact" shadows. Adding the Ambient_Occlusion node to your floor material will improve this dramatically.
The neat thing about using it on the material, instead of AO on the light, is that you can restrict this expensive operation to a subset of your scene items, and you get more control with regard to different parameters in different places, and also it just works better than Light based AO.
I've done a bunch of experiments with regard to quality and render time. Knowing the following info will help you skip a lot of wasted time.
Setting Samples more than 3 is important. 4 is clearly better than 3 and not much slower. 5 is modestly better and not much slower. 10 is great but much slower. More than 10 is not worth it.
The MaxDist parameter controls how far the effect goes. I have no idea what the units of this parameter are. I find that 30 to 50 produces good results in most cases.
The Strength parameter seems to do nothing. 0, 1, .5, all produce the same results. No matter - the MaxDist parameter pretty much also controls the strength of the effect. Lower values produce less shadow.
In Poser 7, Irradiance Caching (render setting) will have an impact on quality and speed. Lower values are faster, and sometimes produce no loss of quality, depending on your geometry. IC 0 to 50 seems to produce pretty much identical results. Always try a low IC for speed first - if the results are good, you're done. Sometimes, though, the maximum value is necessary for quality, but you get a huge increase in render time. Note that if you type in 100, it often resets to 99 or 98 - wierd. Ignore that. It works.
I've attached two renders to demonstrate. I was messing about with refining my leather shading techniques, and was unhappy with the final render, on the left. It still looked fake. Adding AO to the ground, I rendered again. The shoe pixels are identical, yet the second render looks more real! It's in the shadows baby.
On the bottom is a screen shot of how to wire the node into your shader. Just plug it into the Diffuse_Value. My render actually used a MaxDist=500, which produced a much broader darkening. This made the shadow go beyond a simple contact shadow, but I liked the effect.
Click the image to see it full size.
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