Scatter/Transmit VS Scatter/Transmit INTENSITY

vwrangler

So, a random question of no great importance of a Sunday night. Mostly, I just want to know: what is the difference between

- Scatter and Transmit

- Scatter and Transmit Intensity.

They're two of the three options in the Base Color Effect toggle in the Surfaces tab.

"Scatter Only" I get, more or less: it doesn't transmit color through the volume and doesn't deal with the reflectance tint, so the base color effect is stronger and brighter.

I just don't understand the difference between Scatter and Transmit, and Scatter and Transmit Intensity. I can see the difference, but I don't understand it because none of the settings seems to change. Unlike switching between Scatter Only and Scatter And Transmit, none of the settings seems to change or disappear, but how Iray behaves changes fairly noticeably.

For example, here's a character with Scatter and Transmit toggled:

And here's the same character with Scatter and Transmit Intensity toggled:

Scatter and Transmit (the top one) is darker -- quite a bit darker, really -- but also seems to show more detail. Scatter and Transmit Intensity, on the other hand, is closer to where I would expect the character to be. (Scatter Only, for what it's worth, seemed a bit too bright and pink, which is to be expected.)

So ... allowing that I can see the difference, I was just wondering what the difference actually IS, since I'm not seeing differences in the settings. (I have a horrible feeling that there's some blindingly obvious different setting that I'm just overlooking -- there usually is -- but, well, if it's there, I'm not seeing it.)

Toonces

I *think* it let's it honor the transmitted and cattering distances as mentioned here: https://www.deviantart.com/toyen-art/journal/How-To-Prep-The-Skin-For-Spectral-Rendering-772870101

But it's a good question. I think it might be a new property based on the lack of information I can find on it.

davidtriune

I've been really curious about this also.

I thought transmit intensity is the same as transmit except that the color that enters the volume isn't considered. ie. just the intensity of light rahter than the tint. 

But then the two pics should be same brightness so i donno.

nonesuch00

It looks like it's just intensifying the scatter & transmit effect. It's like replacing a 40 watt bulb with a 100 watt bulb. Your renders show that.

Fishtales

For what it is worth  Taken from the Documents.

Scatter Only - Diffuse is layered over Transmission and absorbs the remainder of any unused reflectance value.

Scatter & Transmit - This works like Scatter Only, except with reflection, and based according to the Base Color's RGB; however, the remainder is sent to the Transmission layer instead of absorbed.