Iray, Strong Rim Lights, Bad Leg Shading

Tobor

I've been doing more renders with strong side and rear rim lights. The lights are spots placed at a distance (maybe 3-8 meters), and turned up quite high. To avoid the stark transition in shadows, I've change the emitter size from Point to a plane geometry, typically a disc with a diameter of 10cm to 20cm.

What I've noticed is that (almost?) without fail, the rim causes the leg texture to appear differently than the torso or other parts. By different, the torso usually has the planned appearance of surface sheen, but the leg texture does not. This results in an obvious transition border between the two textures. It mainly happens on the side "opposite" the rim -- that is, if the rim is on the right, it's the character's left leg that is affected, as that leg is more likely to have direct rim light falling on it.

I've verified it's not just an issue with the textures themselves. The surface settings are the same for all of the skin textures (except for the maps of course), and the problem does not appear when the rim light is removed, or turned way down. I tried it on numerous characters from different sources, including the stock V7 maps, and it's there. I'm using the latest 4.9 public beta/release candidate.

Anyone else seen this? Is there a known fix? I was thinking maybe it had to do with the orientation of the map, but both torso and legs are vertically oriented. Perhaps its the way the UVs are done.?

DustRider

I haven't seen this, maybe posting an example or two will help, and prompt a response

TheKD

If this stupid mesh reproject finishes sometime soon, I will see if I can replicate it. Are you using NGS2 or anything like that?

Ok, I set it up how you said, I think. V7 skin on her, I only have one rim light in the scene, from behind and left, here is what I got. Looks odd, as if the light is shining right through the mass. Also happens a bit on the torso and her right shoulder too. Did two renders, one with lumens cranked way up, then one backed off a bit on the lumens.

On a side note, it appears the shadow on the floor is going the wrong way....    Added a wider view where it can be seen that the offending spotlight is really on the left lol.

Tobor

Thanks for the reply. I tried with lots of stock characters, and while I have NGS2 and other add-in skin shaders, I'm not using them. To make sure I wasn't going crazy, I copied the torso material to the leg material, then updated the maps. Same problem. It's not the textures themselves, because without the rim light there's no demarcation, and I can't believe texture sets from so many vendors, including Daz itself, would have the same mismatch.

I think your demonstration is showing something a little different though, a well-known abberation in Iray (and similar renderers) where the underlying geometry isn't detailed enough for texture, and so there can be rough shadow terminator. The effect I'm talking about you won't be able to see if she's wearing shorts, as the texture seam is right there. You have to zoom in.

I might post an example, but it'll have to be an extreme closeup because of the nudity rules here. I just wanted to see if anyone else had noticed this. My lighting technique with strong rim lights isn't all that common.

 

zaz777

I had a similar issue the other day.  While it doesn't sound exactly the same and was with G2F, it might shed light on the issue or be useful to others.

I applied some veins maps I'd made to the Translucency Color channel.  The way the maps were made intended them to be used in a LIE as they were PNGs with transparency for everything except the veins, but I had applied them directly without a base.

The results, in both renders and the viewport in NVIDIA Iray mode, showed the Shoulder surface on one side of the model glowing brightly with the Translucency Color as if I had way too much SSS/Transluceny dialed in.  Part of the Face exhibited the same glowing.  I believe I was using the full BOSS Potrait Light Set for that render, which I've rarely used due to how slow it renders.

Very strange that even though all the limb surfaces had all the same settings, only one of those surfaces glowed.

Even stranger was only part of the Face surface glowed, from about the eyebrows down and I believe the lips were unaffected.  I believe the reason only part of the Face surface was affected is because of some sort of shadowing effect from the hair skullcap cutout.

All the problems went away when I put a layer below the vein maps via LIEs in the Translucency Color channel.

Your problem does sound different, but perhaps they are related.  There definitely is something strange with the way either DAZ Studio or Iray is dealing with the SSS/Translucency settings in iray uber surface.