Z-depth behind transparent objects

[beeemtee]

Hi,

I'am trying to export Pz behind a constant material with an opacity map, but mantra doesn't behave as I expect. It gives slightly different results with MP and RT renders, but the results are similar. At the transparent areas it gives a higher Z value than at the opaque areas. Apparently the returned value is the sum of the Z of the transparent object's and the one's behind.

Is this the intended behavior? Am I missing something here?

The other question is that how is it possible to export the Z value of the object behind the transparent area?

Thanks in advance.

bmt

[Jason]

You should be unpremultiplying Pz by Alpha in order to get to your real z value. You can also try change your "Sample Filter" to "closest"

[beeemtee]

Thanks,

but I'm afraid I still don't get it..

Setting the sample filter to 'closest' gives a more reasonable output, the Z of the transparent object. What I need is the opposite of this: the Z of the farthest surface. It seems that there is no such setting.. (there is a 'farthest sample filtering' option in the 'pixel filter' settings, but that does't affect my results in the desired way)

I also don't grasp the unpremult thing you suggest. The alpha is 0 at the pixels in question. I don't see how would it help to unpremult with that..

bmt