I’ve had some time to come back to this and play around with it and render a few images to show what I’m talking about. I’ve found several other posts around the internet where people are having the same results as well.
So my go to mental ray shader (only bringing MR into it cause it’s the only other renderer I know and I’ve used it for over 10 years) has a really simple setup, there is a translucency color slot and a translucency amount slot. This is on the shader level. I plug a two sided texture into my leave color with a front and back and the same texture into the translucency color. I can increase the amount to make the leaves more translucent like a maple, or less translucent like an oak. The transparency of the leaves is lowered slightly to allow light to filter into the tree interior making some nice bounced lighting.
The branch on the left has light shining through the backside, the middle branch has direct light shining on top and the right branch has light coming through the topside of the leaves. The main thing here is that you can’t see through the leaf that is only lit by direct light, which is almost always how things react to real light. Looking at the backside with sun coming through doesn’t show the front side either. I’ve not been able to recreate this in Vray.
What i’m running into with the vray2sidedMtl is that the translucency is not coming from the amount of light shining on the surface as it would on a real translucent object. The translency tex slot just blends the front and back materials together which you would never every want to happen. The force single sided attribute is letting some light though, but this is not controllable. When my supervisor says to make the leaves more translucent, I don’t see a way to do that.
Here’s what I get in Vray:
Translucency 0, you get the back side of the leaves as expected.
Translucency 0.5 (most people that I’ve come across recommend using a 50% grey texture with black veins). Now i’ve got a slight bit of translucency, but I’m seeing the front side of the leaf blended though… why? You would never see the front side of the leaf, you would see the back side lit with the light from the front:
Translucency 1.0, more translucency, looking better, but now I’ve got even more of the front side of the leaf showing through. This looks completely wrong.:
I jacked up the color gain on the front and back, which increased the translucency, but at 1.0 translucency from the other side, the leaves are now showing the back side through:
I found this page http://help.chaosgroup.com/vray/images/stuff/leaf\_tutorial/ which seems like some of the nodes in there are solving these problems, but this looks like it’s ancient and I can’t seem to replicate that in maya.
I found this, which looks like max, I don’t have a override shader:
I know that this an old thread, but I find myself in the same spot and might be able to suggest a workaround.
The 2sided material is far from perfect. The leaves look nice enough, especially against light - but the shader does not transmit light as it should. The shadows of the leaves are not influenced by the translucency setting of the 2sided material resulting in unrealistically dark spots.
A potential workaround is:
Use a Vray override material for the leaves. Use the 2sided material as base material (without any changes). Create a refractive version of a single side of the leaf (from the front or back slot of the 2sided material) - with “affect shadows” checked! Put this into the shadow slot of the override material.
You can now control the amount and color of light passing through the leaves with the refraction settings of that shadow material. It’s a tradeoff between softer, more colourful light beneath and inside a canopy and the contrast and definition provided by hard shadows.
This response on Peter Guthries blog post about making leaves seems to come to the same conclusion I do:
Haha thanks Peter! Good to know you think I’m not crazy. (I WAS starting to wonder.) If I’m using the normal 2sided material approach, I think there’s an acceptable amount of blending and SSS somewhere around 96 gray. That’s what I’ve been using so far.
However, I’d love to see a material that worked flawlessly. I’m thinking it should be quite easy to program. The transparency factor could be ignored alltogether. You basicly never want to see a blend between front and back material. What you want to take into account is the difference in lighting between the front and the back. If the front material is more brightly lit than the back material (I’m talking viewing front/back here), there should be no blending. If the back material is lit brighter, the difference in brightness should be added to the front material. Also, I think there should be a slot for the SSS color, instead of using the front/back material diffuse color. Since a leaf’s translucency color is mostly due to the green chlorophyll, it should be easier just having to set the desired SSS color, than having to take the diffuse colors of the individual materials into account.
Sorry for the long winded post here, maybe I’m nuts or doing something really wrong, it just seems kinda weird. Thanks for taking the time to check it out.
