how do i eliminate reflectivity in 'transparent' areas of a material?

[probitas]

all -

i'm trying to achieve the vray2sided translucency effect outlined by peter guthrie here: http://www.peterguthrie.net/blog/2009/11/

so i'm using his maps, combined into a vray2sided mtl. it's pretty much there, as far as translucency goes.

i seem to be having problems with the specular map. i've applied it to the fresnel perpendicular channel, and left parallel black. the image preview shows some reflection on the outer areas of the material globe which should be transparent. and, you can see in the attached image where that reflectivity shows in leaves at certain angles.

so the question: how can i get rid of reflection in areas that are supposed to be transparent?

thanks for any help.

VfSU v. 1.48.89, PC

[TOM_cg]

Re: how do i eliminate reflectivity in 'transparent' areas of a material?

silly answer, but did you try with a correct transparency texture in the reflection slot of your materials ?

[probitas]

Re: how do i eliminate reflectivity in 'transparent' areas of a material?

not silly at all. i am not aware of a transparency slot in reflectivity. is there one?

i've tried using both an alpha mask and "use color texture for transparency in the Diffuse layer. - obviously with the same result.

I've also tried using the alpha in the reflection layer - in fresnel "perpendicular" channel, "parallel" channel, in the "filter" map position, and in either/both map slots of 'highlight' and 'reflection' 'texture' in the reflection layer...

as you can see, i've run out of logic to solve this, and i'm just trying random things!

[TOM_cg]

Re: how do i eliminate reflectivity in 'transparent' areas of a material?

plz, send me your exported vismat...
I'll check it and get back to you ( on monday, I'll go camping/biking for the rest of the week )

I'll also read the Peter's blog to see the result your are expecting to get.

cheers

[dkendig]

Re: how do i eliminate reflectivity in 'transparent' areas of a material?

here's a fun one for ya, you can actually open the .vismat file and read it. It's text now. You can actually copy and paste stuff from your .vismat file in to the forum, same with visopts. I don't know how useful it will be to anyone, but hey, the option's there.

[probitas]

Re: how do i eliminate reflectivity in 'transparent' areas of a material?

TOM,

thanks a lot for your willingness to help. i think i figured it out just now... the original reflection map that i downloaded was that of the leaf's specularity against a 50% gray background. i changed the background to black and that solved the problem. i had previously tried using a png with transparent background, thinking it the same thing, but obviously it's not! you can see the result below, including the correct alpha of the render.

i've attached the vismat here in case you have interest.

and dkendig - damn that's a lot of code! thanks for the tip.




www.umich.edu/~probitas/mapleleaf.zip

[dkendig]

Re: how do i eliminate reflectivity in 'transparent' areas of a material?

probitas - you can use a png with transparency, but you have to use the texture for the color texture, not the transparency, and you have to check the checkbox labled "use color texture for transparency". We extract the alpha channel from the texture used as the diffuse layer's color texture (assuming that the texture has an alpha channel), and then use that alpha channel as the diffuse layer's transparency texture. If you don't have that option checked, then we ignore the alpha channel of the diffuse layer's color texture, and only use the diffuse layer's transparency color or transparency texture.

If the alpha channel has a 50% transparency though, you would see the same output you'd get from using a transparency texture that uses a 50% gray instead of black. The difference is, you can't look at the alpha channel of the diffuse color texture in our texture editor, so the only way you would know for sure that the alpha was 50%, is if you opened the texture in an image editor like Photoshop, and looked at the alpha channel. If you were using one texture for your diffuse color texture, and another for the diffuse transparency texture, you would be able to easily see the source of the issue in our texture editor by previewing the transparency color texture.

So as you can see, there are some pluses and minuses to using either method. One way requires more texture files, the other will hide the transparency texture that is being used.