Scalp on certain hairs showing on face as grain shadow

shaneseymourstudio

I just ran into this issue. I had not noticed it until swapping to the latest Beta, 4.11.0.236. The hair that I had offered an option under "Adjusting"where I was able to set "Adjust-ForeheadDepth" to -14% which worked for this character. It didn't seem to shift anything else and allowed the cap to go under the face surface enough to keep from showing up in the render.

CO3DR

I was having a problem like this with @GoldTassel's GeeGee Hair on a Genesis 8 character. The problem was dark marks on the forehead. In my scene, my character was not at World Zero, and I was using Iray with an HDRI dome. I had previously had problems with hair scalp poke-through using Rasta Hair, and those problems weren't really connected with the lighting or position though.

I tried IceColdRender-er's proposed fix, but GeeGee Hair doesn't have Volume Scattering on the Surfaces tab.

So, like a monkey trying different combinations, I made the problem go away by changing "Displacement Strength" on the Surfaces tab. First, I made the map for Displacement Strength the same as the Transmap JPG. I don't know what either of these mean. Then, I set the Displacement Strength up as high as sliding it to the right would make it go (which is 1.94, whatever that means).

However, this wasn't the first thing I tried. I first tried using Tools->GeometryEditor, and using a bunch of its tools to made certain polygons not visible. I guess there is a way for folks more proficient with Geometry Editor to vastly increase the number of polygons so you don't end up with the "stepped look", but this also got me into a problem where I did want this hairstyle to be dark under the part of the hair, and I couldn't find a way to make it look nice. I also had to move my Perspective View to INSIDE the characters head (and make the character NOT VISIBLE) while selecting the polygons but this could simply be my lack of proficiency.

The second thing I tried was what I call "Small Hair" by scaling the "Head" node of GeeGee Hair to 98.3%, which also had a pretty good result but it's hard to remember where to find this Scale (ie, you HAVE TO GO TO A SUB-NODE). But, I knew this wasn't a general fix because it didn't work with Rasta Hair.

After changing Displacement Strength, my render doesn't have the dark marks anymore. I don't know why. I don't see railroad spikes protuding out of the back of the character's head, but that isn't part of my rendered image anyway. I do wonder if creators of hair products all need to add "Apply This First!" to their products, or if there is another way to get transparency on the visible scalp parts of the hair.

(I'm posting in response to THIS discussion because it was the most helpful discussion of this problem when I searched "forum scalp cap visible hair site:www.daz3d.com")

CO3DR

Just wanted to add that later today I tried to setup the core elements of the scene again from scratch, but with the figure very close to World Zero, and GeeGee Hair worked perfectly! (no dark marks)

Syrus_Dante

I guess beside of the issue with Iray and that the character is not placed at the Zero World position, the issue with the artifacts on the forehead comes from intersecting mesh geometry of the figures head and the hairs scull cap. The scull cap may be invisible on the forehead but usualy the edges of the mesh reaches the eye brows.

The scull cap of the hair item can be the exact copy of the genesis figure head mesh geometry but there can still be intersections. By default the scull cap part of the hair is invisible on the forehead due to the opacity map.

The genesis figures are using the SubD modifier to subdivide the base mesh even with different resolution levels in preview and by render time (see Mesh Resolution settings in the Parameters pane) and the current character on the Genesis figure also uses a displacement map on the forehead, while the hair items I've see so far dosn't use the SubD modifier see Mesh Resolution: Base. This can cause slight mesh intersections that Iray seems to have issues with while the figure is not placed in the center of the scene, at least thats my explanation of the artifacts.

It seems with Displacement Strength silder in the Surfaces pane you pushed the head scalp further away from the head resulting in no more intersecting meshes and the artifacts are gone. To me it dosn't seem like a good solution that will not work for all hair items and it seems to depend on the gray value on the forehead area of the Displacement Map image texture applied to the hairs scull cap while this is actualy blank space not used in the texture.

My suggestion

You may want to try to add a Smoothing Modifier to the hair. Select the hair then go to Edit>Figure>Geometry>Add Smoothing Modifier. I add this almost everytime to hair items it prevents poke thrughs resulting in better fitting hair. The settings can be found in the Paramertes pane under Mesh Smoothing. By default if you fit the hair to the genesis figure the Collision Target is set automaticly to be the genesis figure resulting in the hair mesh colliding with the figures head and pushing the hair further away from the figures head. You will notice a progess bar and a slight delay of the Smoothing Modifier calculating the collision while you pose the figure or dial some morph sliders. There is a way to bake the smoothing modifier collision shape of the hair to a morph and add this maybe to the character shape morph generated in the hair item to prevent the Smoothing Modifier delay.

By default the settings for the Smoothing Modifier are Smoothing Iterations: 2 and Collision Iterations: 3. The mesh Smoothing effect with higher Iterations can cause fine hair strands to collapse to prevent this you can set the Smoothing Iterations to zero. Higher Collision Iterations can help to better detect mesh intersections. All in all knowing how to setup the Smoothing Modifier can be useful not just for the current hair issue.

MIH_BAD

Thank you Sir. It works and now I can do some quality work. It was horrible. Thank you for taking the time to let us know how to fix it!  

Syrus_Dante said:

I guess beside of the issue with Iray and that the character is not placed at the Zero World position, the issue with the artifacts on the forehead comes from intersecting mesh geometry of the figures head and the hairs scull cap. The scull cap may be invisible on the forehead but usualy the edges of the mesh reaches the eye brows.

The scull cap of the hair item can be the exact copy of the genesis figure head mesh geometry but there can still be intersections. By default the scull cap part of the hair is invisible on the forehead due to the opacity map.

The genesis figures are using the SubD modifier to subdivide the base mesh even with different resolution levels in preview and by render time (see Mesh Resolution settings in the Parameters pane) and the current character on the Genesis figure also uses a displacement map on the forehead, while the hair items I've see so far dosn't use the SubD modifier see Mesh Resolution: Base. This can cause slight mesh intersections that Iray seems to have issues with while the figure is not placed in the center of the scene, at least thats my explanation of the artifacts.

It seems with Displacement Strength silder in the Surfaces pane you pushed the head scalp further away from the head resulting in no more intersecting meshes and the artifacts are gone. To me it dosn't seem like a good solution that will not work for all hair items and it seems to depend on the gray value on the forehead area of the Displacement Map image texture applied to the hairs scull cap while this is actualy blank space not used in the texture.

My suggestion

You may want to try to add a Smoothing Modifier to the hair. Select the hair then go to Edit>Figure>Geometry>Add Smoothing Modifier. I add this almost everytime to hair items it prevents poke thrughs resulting in better fitting hair. The settings can be found in the Paramertes pane under Mesh Smoothing. By default if you fit the hair to the genesis figure the Collision Target is set automaticly to be the genesis figure resulting in the hair mesh colliding with the figures head and pushing the hair further away from the figures head. You will notice a progess bar and a slight delay of the Smoothing Modifier calculating the collision while you pose the figure or dial some morph sliders. There is a way to bake the smoothing modifier collision shape of the hair to a morph and add this maybe to the character shape morph generated in the hair item to prevent the Smoothing Modifier delay.

By default the settings for the Smoothing Modifier are Smoothing Iterations: 2 and Collision Iterations: 3. The mesh Smoothing effect with higher Iterations can cause fine hair strands to collapse to prevent this you can set the Smoothing Iterations to zero. Higher Collision Iterations can help to better detect mesh intersections. All in all knowing how to setup the Smoothing Modifier can be useful not just for the current hair issue.

 

deepred6502

Had the same issues here with a scene full of G8F characters. I managed to fix it by adjusting the hairdos slightly larger off the characters' heads, and shifting the scene & viewports to the 0,0,0 centre axes.