tree leaves - opacity vs. refraction

[dynaman]

OK, sorry if this has already been addressed elsewhere, but i couldn't find it using the search engine.
i have been trying for weeks to determine how to best render trees that have alpha channels for the leaf geometry. i had been using the alpha under the refraction channel, but in some areas the rectangular shape of the geometry becomes evident (see image below). if i use the alpha in the opacity channel, the leaves do not render with a consistent opacity and the render times are about 3x longer (see image).

when using refraction the leaves render perfectly when they are in front of most surfaces, but when they are in front of glass, for example, i always end up with the ghosted outline of the geometry. can anyone explain how to correct this problem, or what technique works best?

thanks

[vlado]

When using refraction, you will have to make sure that the reflection/refraction depth for your materials is high enough - for a test, you can turn on the depth limit in the global switches rollout and try higher numbers - e.g. 10 or more and see if it helps.

Best regards,
Vlado

[Aldaryn]

Hmm, alpha maps should be fine, and quite quick too, if you turn off filtering for the maps used to get the alpha, and there also seems to be something wrong here. You should get a constant opacity not depending on, for example, the face angle. What are your shader settings? I'm rendering here tons of leaves with opacity maps, and I never had anythink like this with them so far.

Best regards,

A.

[mikeh]

Hmm, alpha maps should be fine, and quite quick too, if you turn off filtering for the maps used to get the alpha, and there also seems to be something wrong here. You should get a constant opacity not depending on, for example, the face angle. What are your shader settings? I'm rendering here tons of leaves with opacity maps, and I never had anythink like this with them so far.

Best regards,

A.

has vray changed recently? My experience with vray is that opacity maps slow it down where it blows through straight meshes. It's why i use mesh leaves instaed of opacity mapped leaves.
mh

[dynaman]

Hmm, alpha maps should be fine, and quite quick too, if you turn off filtering for the maps used to get the alpha, and there also seems to be something wrong here. You should get a constant opacity not depending on, for example, the face angle. What are your shader settings? I'm rendering here tons of leaves with opacity maps, and I never had anythink like this with them so far.

Best regards,

A.

yes, i have the filtering turned off. which shader settings are you referring to? i have am using glossy hilites on the leaf materials (not true reflection, just the soft hilite). the thought occurred that this could be the problem. i haven't had time to re-test since posting.

[Aldaryn]

There seems to be something wrong with opacity mapped things and fresnel reflections, but I don't think that's your problem.

Without filtering opacity mapped things render here just fine, and with a very little impact on render speed. Recently we even switched to opacity mapped grass (like what you see in game engines, but a more detailed, and dense solution) and it renders far more faster and reliable than displaced one, not to mention it looks better. A very, very large area with more than five million opacity mapped planes renders quick and fine.

Only drawback is the lack of alpha contribution from the opacity maps...

Best regards,
A.

[ene.xis]

Recently we even switched to opacity mapped grass (like what you see in game engines, but a more detailed, and dense solution) and it renders far more faster and reliable than displaced one, not to mention it looks better. A very, very large area with more than five million opacity mapped planes renders quick and fine.

can u show some examples?
lately i ve been having some displacement headaches and i ve been thinking in trying something like that...but didn t manage to do some tests yet...

[Aldaryn]

Oh, I will. I'm working on a grass demo image right now.

Best regards,
A.

[ene.xis]

nice!

thanks Aldaryn

[Aldaryn]

Well, on second thought, I've been "working" on that demo scene for two weeks now, and since we barely get any sleep here in the office, I don't think it will be ready anytime soon, so as a "proof of concept" here's a shot for a work I've recently did. This is a 100% crop from a 5K rendering, this is why the road is so lowres, and lacks nicer texture work. The grass itself was very, very subtle in the final prints, but I used this job to stress test the technology itself. The site featured over two thousand square meters of grass, hundreds of opacity mapped onyx trees, and approximately twenty thousand opacity mapped leaves scattered by hand one by one. Was fun to do...



I'm not really allowed to post the full thing however, so sorry for the crop.

Best regards,
A.

[ene.xis]

Wow!
that looks pretty awesome!

but...

and approximately twenty thousand opacity mapped leaves scattered by hand one by one. Was fun to do...

...twenty thousand hand scatterd planes!!
no wonder u guys get no sleep!
i ll try and get my hands into it in the upcomming works...(hopefully)

[Neilg]

Down already?

[re:FORM]

Lovely grass!

How many different grass maps did you use for that? What shape was the plane the grass is mapped to?

[Aldaryn]

Thanks! Well, in this particular test there was only one map. Not even a hue variation... but my intention was to test how efficient the thing renders. The grass is mapped on planes slightly bended in the Z axis to give better cover viewed from above.

The one I'm working on has twelve maps, six for individual grass blades, three for smaller lumps, and another three to add some smaller plants to the mixture.

Oh, and there's glossy reflection and SSS on the grass.

Best regards,
A.

[Neilg]

I refuse to believe that could be faster than displaced grass. Ive done some tests with a similar technique before but it was for a feature of the image along the side of a road, never tried to do it en masse.

Also your image doesnt work for me? I'm not sure how anyone else is managing to see it.