Odd interaction between mesh lights and hair
tl155180
Posts: 994
Hi All,
I've got a problem here that I was hoping someone could put me straight on please. I'm lighting a scene with the Iray dome & sun plus a bright overhead mesh light (flat plane) and a mesh light attached to the camera. As you can see from the images it all works fine if the mesh light on the camera is turned off. But when I switch it on its not lighting up a section of her forehead thats influenced by the hair prop (you can see that without the hair and the camera light on its ok too).
Anyone got any ideas as to whats happening here please? The overhead mesh light isn't causing any problems, so I don't get why the camera mesh light should be because they are basically the same setup.
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Comments
Is the mesh light casting a shadow on her head, maybe? :-) Just a guess, so please ignore if it's a stupid one.
Or if there are "barndoors" or something on the light, the light beam could be too sharply defined.
Theres no shadow on the image without hair, so if it is then the shadow is somehow originating from the hair. That wouldn't make much sense though cos the camera light is basically pointing straight on.
If you look at the first 2 images closely though you'll notice that the darker forehead section is the exact same tone as in the image without the camera light on - so more accurate to say that the camera light is just having no impact upon that section whatsoever.
The hair prop is causing it... I just can't work out how or why.
Check that the cutout opacity map is not being gamma corrected (click on the map, in the scalp surface and go to Image Editor). That can be caused by the map not being pure b/w...and if gamma is set to 0, in the image editor box, then Studio is 'guessing' and is probably guessing wrong as to whether or not to apply correction to the map.
It is being corrected by the looks of it. Do I need to adjust these settings then?
In Studio, a value of 1 means 'don't guess'...and is what should be used for control maps.
So, it's right.
The other thing is to make sure that the cutout opacity is the same for the scalp and the rest of the hair, since it seems to be fine.
Which hair is this, by the way?
Yep, its the same. Its 1.0 for all aspects of the hair.
Its http://www.daz3d.com/pixieperfect-hair-for-genesis-2-female-s
Hmmm, just noticed that the camera mesh light isn't impacting upon the eyes either. So its not limited to the hair. This is really strange...
Ok, this is really weird. I just moved her and the camera slightly on the x and z axis and now the problem has disappeared. Its obviously something to do with where shes placed in relation to the various light sources. Thats really annoying because its going to rule out putting her in certain locations.
I've had similar problems with other DO/goldtassel hair...and not just in Iray, but in 3DL, too.
Yeah its really strange. I've been moving her all over the place and taking quick snap renders. It only occurs when shes in certain locations on the x,y,z grid, so it must be something to do with how the 2 mesh lights are interacting with each other and the Iray dome when shes at certain distances from them.
Thanks for trying to help guys. Looks like this is more problematic than I originally thought.
May be a silly suggestion, but make sure that the backgorund on the scalp trans map is 100% pure black.
I'm not getting it today, but I can't remember what lights I used. I do remember that I wasn't getting it with HDR lighting.
If it wasn't I'd be experiencing the problem no matter where I placed the model wouldn't I? This sounds like something I'd have to check in GIMP, so might be a bit outside my area of knowledge.
Edit: Actually it wasn't that hard to check. It is pure black.
If it doesn't occur at 0,0,0 but does at other locations, this is a known bug. It has been reported by several people here, and I confirmed it by following the steps outlined by another user. In his/her case, it was a spotlight or point light, so I don't think this is limited to just mesh lights. The effect showed up in G2F eyebrows, which also use transmaps.
Ah ok, thanks Tobor. I think I can work around it for now.
Ah, now I see what you mean. :-) OK, in that case, I would think Cho's suggestion about the skullcap transmap might make sense.
Can you just make the surface of the skullcap invisible? Opacity or cutout value?
That doesn't look very good with this hair. Its ok though, as long as I don't place her in certain areas then it doesn't happen. Thanks for your suggestions.
You are welcome. :-) One last idea -- on the morphs, there may be some option like "hairline in" that'd make the skullcap go inside the forehead.
If not, it sounds like you've gathered some workarounds. Good luck with the rendering!