The hair is a solid geometry, retopologized in 3DCoat from an earlier, lower resolution version.  Because it is solid, it uses transparency to hide certain areas of the geometry.  Because it is a retopo object, the geometry may be a bit weird.  But that didn't really matter when I built it, since the materials hid everything as desired.  Somewhere along the line that stopped working properly and now I have a shadow ridge at the bangs.

Does anyone have any suggestions?  Mat tricks?  Altered shadow bias settings?  Anything short of tearing up the geometry, or rebuilding from scratch, to fix the problem?

Are the normals correct in the obj? You may be able to select normals forward on the Poser Surface tab to correct it.

You also didn't mention the lighting type used, and if you set the trans map to 1 gamma.

Lighting is standard Poser lighting, rather than IDL.  Two point lights and a spot, all using raycast shadows.  I'm not using gamma correction at all.  It's turned off and all textures are set to inherit gamma settings from the render settings.  I have normals forward checked everywhere it is available in the shader I've set up, but have tested turning it off, without any evident effect, while trying to solve this problem.

There could very well be some problems with the hair object normals, but I have no idea how to identify or fix them, if that is the case.  :unsure:

You could try importing the geometry into poser and select normals forward and see if Poser can correct it on import.

maybe try it with bill's thin glass shader, depending on poser version.  attach fresnel node to trans chan, trans_edge = 0, trans_falloff = 0.  both fresnel node colours (in/out) = white, then att. hair transmap to inner.  if no fresnel node, use edge_blend node.

Hmm.  I tried re-importing the geometry with "make normals consistent" checked.  Results were identical.  :sad:

Interestingly, attaching a fresnel blend node to the transparency map did remove the problem.  Unfortunately, if the refraction angle is set adequately to have this desired effect, it also makes much of the remaining hair semi-transparent where it should be opaque.  :cursing:  :lol:  :crying:

I'm going to have to tear the %*%@#!! geometry up and bring it back into Poser in separate pieces, right?  I can see where this is leading.  I'm going to need separate parts so I can just turn off shadow casting on the bangs....  :unsure:

ray trace shodows will fix it.

Quote - ray trace shodows will fix it.

Ooh, I wish it were so simple.  :lol:  :crying:  I'm already using ray-traced shadows on all of the lights, unfortunately.

I've checked the transparency map to make sure there are no oddities there, and it looks correct.  The visible seam seems to be a shadow, but I'm not completely certain.    If I remove the trans map and make the whole thing transparent, the problem disappears.  With the trans map, there it is.  But the area which is showing when it shouldn't is a separate material, fully transparent, with no trans map at all.  Weird stuff happening here.

I could get intersection shadow with my solid hair model when trans_falloff = 0.6 (or bad transmap, with non-white or non-black), but no intersection shadow with falloff = 0.  this means that intersection shadow with fresnel_blend thin glass shader gets progressively worse as IOR increases.  even shadow-mapped lites will work, but raytraced shadows are preferred.

Quote - I'm going to have to tear the %*%@#!! geometry up and bring it back into Poser in separate pieces, right?

I suspect you are barking up the wrong tree, thinking about the geometry. My guess is that this is a shader problem.

Quote - If I remove the trans map and make the whole thing transparent, the problem disappears.

That sounds a lot like the classic Transparency_Falloff is not zero or black parts of mask are not true black problem, as mentioned by Miss Nancy.

Have you checked these things:

Transparency set to 1.
Transparency_Edge set to 0.
Transparency_Falloff set to 0.

Use a colour picker to check that the fully transparent parts of the mask are pure black, #000000.

Plugging the mask into the Specular_Value, should prevent you getting specular highlights on the transparent parts.

If you show us a screen shot from your material room, it may provide some clue.

Here's my shader for the hair material which seems to be causing the problem.  I pulled the trans map into PSP yesterday and checked the areas of black and white to make sure they were correct.  I also generated a new UV bmp using UVMapper and overlaid it on the trans map, to be sure all the areas were correctly covered.  As far as I can tell, everything is fine.  The problem vanishes if the problem material has the trans map deactivcated, becoming completely transparent.  It also goes away if I deactivate shadow casting for the hair geometry - hence my thinking that splitting the geometry might fix the problem, albeit while leaving the actual cause a mystery. 

Note that I can minimize the effect by moving the lights to control where the shadows fall, so I can work around it a bit.  But I'm pretty sure this shouldn't be happening.

my guess would be to drop fresnel_blend IOR from 5 to 1.000. 

Oh.  Umm.  Yesterday I tested detaching the fresnel completely - I detached the diffuse and specular nodes which implement it - and the problem was still there.  I think the earlier renders I show above, with the flat texturing and specularity, have been simplified that way.  I'll try some more things in that direction, though.  :unsure:  Thank you.  :thumbupboth:

You haven't set Transparency_Edge to zero.  It's 1 on your screenshot.

Quote - You haven't set Transparency_Edge to zero.  It's 1 on your screenshot.

Ooh.  Good catch.  I'll change that, in the current tests.  I ignored it because making that change yesterday didn't seem to affect things either way, so I just left it on.  But the shader should be cleaned up for the sake of testing.

I checked that area of the transparency against the UV map yesterday and those black areas are in the blank space on the UV.  If Poser is holding that against me, it has some problems, apparently.  :lol: 

The link you provide is interesting, but I may be a bit dense.  How would that be affecting my situation? 

maybe try losing displacement.  some users of some versions have mentioned difficulties with displacement and ray-traced shadows.  lose bump as well, to confirm it isn't the problem.  unless somebody already mentioned these.

refractive fresnel shader, e.g. for gems and thick glass, is notorious for contact shadows in recent version(s).

I have to confess that I am an ignoramus about most aspects of the Materials Room.  :lol:  I am one of those who tinkers with shaders and settles on what looks good to me, without knowing what I'm doing or why it may or may not be the correct thing to do.    So there's always plenty of room for one of my shaders to be having some bizarre and unintended effect like this.  Hoo boy.

The attached shows the UV map overlaid on the transparency.  I don't know much about texturing or the complexities of UV-handling in different software packages, but based on everything I think I know, the black areas on the transparency should have no effect on the final material.  Based on the attached, is there a possible risk of trouble?

I think you have black and white around the wrong way.  A transmap would generally have white for the strands and black for the transparent areas. 

Quote - I think you have black and white around the wrong way.  A transmap would generally have white for the strands and black for the transparent areas.

Yes, that is true, but that is a result of the setting I used on the UV layer in PSP, to make the relationship of the transparency and UV map as visible as possible.  I used "exclusion", which inverted the colors of the underlying trasparency layer.  The actual trans map in use has black and white the right way 'round.

Umm.  Sorry about my ongoing lack of clarity, today.    I begin to wonder if I may be having a day on which I am even more stupid than usual.  :lol:  In which case, any use of Poser may just lead me to baffling problems which I can't explain well.  :unsure:

If I had upload access to my site, I'd post the hair and textures for others to study as desired.  I haven't been able to log on to the server for some time, however....  :sad:

To emphasize this point, I have here tested rendering with that hidden material shown in red.  I don't see how the trans map on the other material could be causing my problems.  Umm.

start by setting texture filtering to NONE on the transmap texture node.  This is often missed by both vendors and tinkers alike.

This will ensure the transparency map used at render time actually looks exactly the same as the transparency you see in an image editor.

oh, another thing, if you have Ambient Occlusion enabled on your light source, try turning it off for now.

I... whaa?... hooba... umm.  Whoa.  I think, I think maybe that worked.  Yes, seems to have... worked?  Wow!  Woots all around!  :woot: :woot:

Thank you, templargfx!  See, I've been using the "crisp" filtering for all textures since it was introduced and explained as being superior to the other options.  But apparently it isn't a blanket solution. 

Now I'm puzzled about precisely why Poser was behaving as it was, due to a Crisp filter on a trans map in a material zone adjacent to the actual problem area.  What did the filtered texture look like to Poser, internally?  And why would it do this weird thing?  But I guess I needn't be too worried about it, now that the problem is solved.  I've got my waldorf salad.  :laugh:

Thanks to everyone who helped here and tolerated me while I panicked and flailed about hopelessly.  :lol:

The most likely reason for the issue is that even on crisp, the edging between the black and white areas of the transmap were being blended together slightly, introducing an ever-so-slight non white (or non black) colour to the edge of the fringe. not being entirely transparent, it casts a shadow