The transparency channel in Poser is not strictly transparency.

When you have just a number, it is the transparency. When you plug something in, it switches to opacity.

Opacity (the degree to which something blocks your ability to see through it) is the complement of transparency.

Using math:

transparency = 1 - opacity

or

opacity = 1 - transparency

So - simple color black (which is indeed zero) switches the mode to opacity. Opacity of 0 means

transparency = 1 - 0 = 1

So when you plug in 0, it's the same as not plugging anything in it with a transparency setting = 1.

I agree this is senseless. There is no point to plugging in 0 if you want transparency = 1. Just set it to 1 and plug nothing in.

The reason it switches is because the original transparency strategy with transparency maps is that 0 is transparent, 1 is opaque. So when you plug in a map (or any node) it has to go into that mode.

The label on the channel is very confusing. It's an opacity channel, not a transparency channel.

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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)