Ambient Occlusion On Object With An Alpha?

[pixelpower]

Hello all, quick question.

I have a polygon object textured with an image of 3 big leaves. (The image includes an alpha channel for transparency, of course)

I would like to know if there is any way to render an occlusion pass that also takes that alpha image into account. Like... Is there some way to feed that alpha into the occlusion shader the render layer override applies to my scene? I don't want to occlude based solely on the geometry as this makes large, square, ugliness instead of leaf shaped occlusion prettiness.

I'm an animation guy, so be gentle with me. I am really getting interested in the lighting / texturing / rendering side of things, but it's all still pretty confusing to me.

I have searched here, but only found one topic that seemed to suggest it was possible...

If there is no way, my only other thought was to remove the leaf objects from the occlusion render layer, but then of course objects behind them will show up in the occlusion render when they should be hidden by the leaves... Unless I apply a black surface shader to the leaf objects to ask as a mask?

Hrm...

Anyways, thanks in advance! This is my current biggest unknown in terms of rendering my short film, so any advice is greatly appreciated!

-Pixelpower

[joojaa]

Yes but it would defeat the purpose and speed of occluison. The idea of occlusion is that it need not go into the internals of the shader which may be slow. Giving you more or less the speed of final gather, so why not then gather?

So use final gather

[pixelpower]

Thanks Joojaa!

This is what you said in the other thread I found in my searching as well. I am embarrassed to say I have never used final gather, and I have no idea how it works. I will go read up on it, and see if I can work it into my scenes. I imagine it is not too difficult, even for a keyframe jockey.

But, just to humor me, can you give me any hints on how one would accomplish this effect with ambient occlusion? I have occlusion set up, and it looks great in 90% of the shots in my film. If there is a way to get those last few shots rendered without starting over with a new technique, I might be up for it. Even if it's not the smartest way to go about it, hehe.

If you tell me, I promise to do my final gather homework.

Or, is the effect I would get from final gather close enough to the effect I would get from occlusion that I could inter cut the shots without a noticeable difference?

Thanks again, I really do appreciate it.

-Pixelpower

[joojaa]

You can gather occlusion, but theres not much point if you can get something better for less time. (occlusion is just a simple substitute fr not having time to gather) Gather interpolates a bit different.

[pixelpower]

I see...

Well, since Occlusion works for 90% of my shots, and is (If what I am getting from your posts is right) faster than final gather, I might want to try to use it for all shots if I can solve my leaf alpha problem. (I have already budgeted my render time pretty tightly to allow maximum animation tweaking. My primary goal in the film is to tell story and show off animation, secondary goal is to make it pretty!)

So far 3 people have told me it is possible to do this, but I'm still trying to figure out how. Based on my fuzzy understanding of the hypershade my guess is to somehow bring my alpha into the mib_amb_occlusion shader and apply that version just to my leaf polys?

Thanks again, sorry to be a pest. I am one of those that wants to know how and why in order to learn more.

-Pixel

p.s. 20,000 posts in your profile! Holy cow! Can I throw away my maya manual and get your phone number? LOL!

[pixelpower]

Any help anyone? Is there some sort of magician's code where people won't reveal their tricks? Is that why people keep telling me that this alpha-occlusion thing is possible, then when I ask how, they get all quiet?

-Pixel