Iray Uber Base - Transmitted Color Image Map

KurzonDax

Can anyone tell me what the image map setting for Transmitted Color is used for? The documentation states nothing about it.  My assumption is that it should allow you to use a UV map to specify the transmitted color across the surface, so if I wanted to vary the color I could do so.  However, regardless of what I use as an image map, the rendered result is the same: Iray acts like I specified RGB 255,0,0 as the tranmsmitted color. This happens no matter what is actually in the image map, and no matter what is specified in the transmitted color field.  If I remove the image map, everything works as expected.  I strongly suspect this is a bug (in both 4.8 and 4.9 beta), but I wanted to clarify the purpose of that image map before submitting a ticket.

Oso3D

As far as I can tell, it does jack all. Which is annoying.

 

mjc1016

Have you tried it like a gel?  I can't imagine it doing much on a volume/object, but maybe a single thickness plane?

 

KurzonDax

To add a little context to this:

Studio v4.9 handles SSS much better (more correctly) than 4.8 does.  I believe this is the result of a bug fix in 4.9.  Because of this, I decided to work on some hyper realistic skin textures.  The issue is that some areas of the body need a different transmitted color than others.  To appropriately handle that, I wanted to use the image map in the transmitted color field to smooth those transitions, especially near seam boundaries. Unfortunately, once the image map I created was added, the resulting render appears that Iray is just dumping pure red out to the transmitted channel.  I then tried the same thing in v4.8 which gave similar results.

I'll try to post some images later today when I'm back at my rendering PC to show what is happening.

Oso3D

Ok, so this may be an insane and annoying idea to handle that inelegantly, BUUUUT...

Maybe try a geoshell with a negative offset, set it to be nearly transparent, and give it a glossy color map? Glossy color acts like a gel for transparent objects, and DOES properly take maps, sooo...

 

 

mjc1016

KurzonDax said:

To add a little context to this:

Studio v4.9 handles SSS much better (more correctly) than 4.8 does.  I believe this is the result of a bug fix in 4.9.  Because of this, I decided to work on some hyper realistic skin textures.  The issue is that some areas of the body need a different transmitted color than others.  To appropriately handle that, I wanted to use the image map in the transmitted color field to smooth those transitions, especially near seam boundaries. Unfortunately, once the image map I created was added, the resulting render appears that Iray is just dumping pure red out to the transmitted channel.  I then tried the same thing in v4.8 which gave similar results.

I'll try to post some images later today when I'm back at my rendering PC to show what is happening.

Did you try inverting the map color? (Maybe it really isn't transmission but rather absorption?)

KurzonDax

mjc1016 said:

KurzonDax said:

Did you try inverting the map color? (Maybe it really isn't transmission but rather absorption?)

Yeah, I tried that as well, thinking along those same lines. Same red result which is why I'm leaning toward bug.

 

 

timmins.william said:

Ok, so this may be an insane and annoying idea to handle that inelegantly, BUUUUT...

Maybe try a geoshell with a negative offset, set it to be nearly transparent, and give it a glossy color map? Glossy color acts like a gel for transparent objects, and DOES properly take maps, sooo...

Interesting idea. A shell with a negative offset never crossed my mind as a work-around.  I might give that a shot this afternoon.  

mjc1016

The only other thing I can think of, if not a bug, is if it's supposed to be a control map...which would mean it would probably need to be b/w(greyscale)...but the location doesn't make much sense for that.

KurzonDax

Believe it or not, I tried using a grayscale control map as well, thinking maybe it was meant to control the transmitted measurement distance.  I'll grant you one guess as to the results.  I'm going to go ahead and submit a ticket on it.  I had hoped to render some examples yesterday, but got side tracked due to my son getting sick.

Thanks for the help, gentlemen!

jag11

KurzonDax said:

Can anyone tell me what the image map setting for Transmitted Color is used for? The documentation states nothing about it.  My assumption is that it should allow you to use a UV map to specify the transmitted color across the surface, so if I wanted to vary the color I could do so.  However, regardless of what I use as an image map, the rendered result is the same: Iray acts like I specified RGB 255,0,0 as the tranmsmitted color. This happens no matter what is actually in the image map, and no matter what is specified in the transmitted color field.  If I remove the image map, everything works as expected.  I strongly suspect this is a bug (in both 4.8 and 4.9 beta), but I wanted to clarify the purpose of that image map before submitting a ticket.

Transmission Color is the color that the light will get as it travels by the interior of the volume, it is controlled by the Transmitted Measurement Distance which tells Iray how far the light must travel in cm inside the volume to reach that color. We can use maps on the surface of a material 'cause it has geometry, but inside the volume it is of no use 'cause inside the volume light only get affected in three ways, it gets scattered, absorbed or tinted or both.

Contrary to 3DL in Iray we have to carefully design materials, we have to design what happens to light at the surface and in the interior of the material. In 3DL artists only focused on creating beautiful textures, in Iray it is only the beginning, there are 2 more things to care about, it is like switching from 2D to 3D, I call this TSV, one dimension is Textures, other is light interaction with Surface and the last is light interaction with Volume.

HTH to clarify.