Quote - But what about Bump channel? Does it work like displacement or in the "traditional" way, that is, 50% gray means "no change" while white/black are positive/negative elevations?

Great question. Bump works the same way, which means that everybody for all of Poser history has been using bump maps incorrectly. However, almost nobody believes me. Mostly this is because the nature of bump mapping often does not reveal a problem. The surface doesn't actually move, so you don't see the "bloat".

But, if you have two surfaces opposed to each other very close together, the virtual bloat becomes evident. Bump mapping does not actually move the surface, but it does calculate things as if it did move it, then retains the changes in surface normal. As a result, if you have two surfaces very close together and facing each other, if you bump them past each other, you will get virtual crossover, and the render will have an artifact.

Most bump maps have sufficient dynamic range (difference between highest and lowest points) that people are able to use a very small bump value as a multiplier. So the overall field value, which is usually .5, does not appear to cause a bloat artifact.

However, if you have a very low dynamic range bump map, i.e. one that is almost entirely mid gray, then you will need to crank up the bump value. This means, for example, that if you have the bump value at .5 inch, and your field is .5, then you are performing an overall virtual displacement of .25 inch.

I will now demonstrate this problem to you, using the lo-res textures that come with M4.

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