Regarding the ImageMap Background=x - this is not a Poser shader node thing, this is a VSS thing.

Recall that VSS copies shader Templates to actual target figure materials, and is supposed to convert the template to a final shader based on what it finds on the figure already, particularly with regard to image map file names.

So when you have a Bump Map in the template, there are two major situations VSS has to deal with:

A) It can find a Bump Map file on the target
B) It can NOT find a Bump Map file on the target

I, as the designer of the VSS script algorithms, am perfectly clear on what to do in case A. I should plug the bump map file into the template shader where you specified the Bump Map. That's clear to you, too, I hope.

Now what is the protocol for case B? I decided to leave it up to you, the designer of the template shader. I just needed to come up with a way for you to instruct VSS what to do in case B.

Are you able to guess?

In case B, VSS will remove the Image_Map node and use what is plugged into its Background instead.

So what you see is template instructions to VSS on what to do in case B.

s.Bump = Sub(ImageMap(Background = Turbulence(.05,.05,.05,8,0,.5,.15)).labelled("Bump Map"),.5) * .03

In Case A VSS rebuilds that for you like this:

s.Bump = Sub(ImageMap("actualBumpHere.jpg"), .5) * .03

In case B (no file defined), VSS rebuids that for you like this:

s.Bump = Sub(Turbulence(.05, .05, .05, 8, 0, .5, .15), .5) * .03

In general, any VSS template shader can have any number of named image maps in it. Each of these is a placeholder to be populated with a filename during synchronization. In the case where no filename is available, the value set in the Background of the image map will be used as a suitable substitute.

If the substitute value is another image map, and it cannot be synchronized either, and the second map has an alternative, it will be used as the alternative to the first image map as well. In otherwords, image map alternative substitution is recursive.

You might notice that in some of the shader I put out, the Specular Map background points to the Color Map. That means I, as the designer of the shader template, am informing VSS that if it can find a Specular Map, use it, but if it can't, to substitute the Color Map instead. Further, you may see that the Color Map has an alternative as well, which is a simple skin-like color.

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