Oh. Hmm. If I understand what you're trying to do, that's impossible in Poser.

For example, looking at the building in your sig, you want to bake the AO shadows into the pink stripe texture where there are corners and crevices on the 3D object? Poser can't do that. The only sort of shadow baking it can do is for the actual render, not for the underlying texture. Other renderers can bake textures, but not poser.

What I thought you were after was something like the attached images. Instead of a normal render (left), you can make a shadow's only render (right). Then you can render over and over without expensive shadows, and combine the shadow render in post. It's only useful for when you're trying to fine-tune shaders and such, and you don't want to wait a long time to get the shadows each time. You render the shadows once, then do all your evolving tweak renders without shadows, and finally combine them in the end.

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Renderosity forum reply notifications are wonky. If I read a follow-up in a thread, but I don't myself reply, then notifications no longer happen AT ALL on that thread. So if I seem to be ignoring a question, that's why. (Updated September 23, 2019)