Spectral rendering causes visible seams with some skin skin materials.

[slitherhence]

So... what the hell am I looking at here? (View full screen, look at the seams.)

Spoiler: Spectral Rendering On, CC Avandrael skin mats

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If I turn off spectral rendering?

Spoiler: Spectral Rendering Off, CC Avandrael skin mats

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And with a different skin mat?

Spoiler: Spectral Rendering On, CC Circe skin mats

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I prefer the CC Avandrael skin for this character (CC Circe looks middle-aged) but without spectral rendering she looks like she forgot sunscreen at the beach and has a hand made of watermelon jello. I could futz with the lighting and fix it, probably... but i'd like to know what's going on here.

I've never noticed this issue with this skin material before (from CC Avandrael) but, for all I know it's always been there and I simply didn't notice. I can't help but think it's not just spectral rendering... but rather some material setting that's causing problems that are only visible with spectral rendering on. This would provide one possible explanation for why other skin materials... even from the same artist (changeling chick) do not have this problem.

Any thoughts?

 

[slitherhence]

I don't think it's a problem with the maps/textures because the seam at the breastacular graft is also visible... but the map used for the graft is the same as the rest of the torso and has nothing special about it at that point on the mesh. But, obviously, it could be some detail I know nothing about due to me being a noob.

 

[slitherhence]

Spoiler: Spectral Rendering On, CC Avandrael skin mat, Scattering Measurement Distance 0.5

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Changing Scattering Measurement Distance from 0.035 (default in CC Avandrael mats) to the value used by CC Circe instead... 0.50. I have no idea what this setting actually does, I'll look into it in a bit. However, it solves the issue with visible seams... but makes the skin tone too dark.


It may be worth mentioning that CC Avandrael uses Chromatic SSS Mode and CC Circe uses Mono.

 

[GrayTShirt]

I see these seams all the time. I just use post-work Photoshop to get rid of them. it's easier for me than having to go through rendering adjustments.

Spoiler: Pre and post-work

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[slitherhence]

I see these seams all the time. I just use post-work Photoshop to get rid of them. it's easier for me than having to go through rendering adjustments.

Spoiler: Pre and post-work

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Thanks for your reply.

I didn't want to fix it in post because, since these seams were going to be visible all across the body in almost every single render, it would increase the amount of work needed for each render significantly. The example you give is very fine and might go unnoticed from a distance typical to most scenes... thus requiring post work only when unusually close-up renders make them visible. What I'm seeing are bold, dramatic seams that can be seen even from several meters away. I've already switched to a different skin material from a different character instead, but I'd like to understand the root cause here.

From testing it has something to do with sub-surface sampling. But I haven't been able to change those settings in a way that resolves the issue but doesn't dramatically change the characteristics of the skin material.

Causes problems:


Doesn't:

 

[GrayTShirt]

What you're doing is way outside my knowledge base. I can't wait to find out how it's fixed! I hope to one day be able to troubleshoot as well as you guys without having to rely on so much post-work.

 

[slitherhence]

What you're doing is way outside my knowledge base. I can't wait to find out how it's fixed! I hope to one day be able to troubleshoot as well as you guys without having to rely on so much post-work.

Unfortunately, it's pretty far outside my knowledge base as well. I have an advantage, however, in that I've spent 25 years as a professional computer repair tech and the last 10 as a professional software developer as well. Thus, problem solving is like breathing for me. That lets me narrow in quickly on the source of an issue but doesn't necessarily translate into comprehension. Especially when I'm this far outside of my existing knowledge base.

I personally don't think there is anything wrong with solving issues in post so long as you balance the additional time taken against the demands of your update cycle. In many cases it can be a big time saver... such as in the case of nvidia's and intel's iray noise filters. I'm already doing a fair amount of work in post... but I'm also still developing my process and trying to find ways to shorten the time I spend on each render. I'm actually trying to do some things I've not seen anyone else attempt. I'm well aware of the reasons why but I think I can overcome those issues. The only question is how much time will it add to the completion (post work included) of each render.

Obviously, the more I understand things like this the more likely I am to spot ways to shorten render times and save time in post. Which, in turn, brings me closer to achieving my goals. Hence why I'm interested in understanding why the problem I outlined in the OP happens even though I've already worked around the issue.

Maybe I should pick up a book on PBR and/or iray

 

[Synx]

This is a bit of a wild guess but I have seen lines like that in other programs when the maps got very sharp edges. Like if you open the map and lay the UV-map of your model on top, the 'information' of the map stops directly y where the UV-ends instead of bleeding out a couple pixels.

You could try opening the SSS-map used for the skin with photoshop of Gimp (free alternative) and smear out the edges a bit, see if that solves it.

If that doesn't work im almost sure it's something related with the maps used. Maybe the seames between the body and the arm aren't exactly the same

 

[slitherhence]

This is a bit of a wild guess but I have seen lines like that in other programs when the maps got very sharp edges. Like if you open the map and lay the UV-map of your model on top, the 'information' of the map stops directly y where the UV-ends instead of bleeding out a couple pixels.

You could try opening the SSS-map used for the skin with photoshop of Gimp (free alternative) and smear out the edges a bit, see if that solves it.

If that doesn't work im almost sure it's something related with the maps used. Maybe the seames between the body and the arm aren't exactly the same

Thanks for chiming in.

Yeah, this was my first instinct as well as I had seen the behavior you describe when tinkering with textures in other engines in the past (mostly games). But, like I pointed out earlier, the maps used for the brestacular graft extend all the way up to the neck and all the way down to the legs... in other words, far beyond the edge of the uv. That's because the brestacular graft is actually using the same maps as the base figure's torso despite the brestacular graft only replacing a portion of the torso. Same problem with the golden palace graft as well. Also there isn't an SSS map in the problematic materials. :-/





So... is there a case where a map can extend well beyond the edge of the uv and still create this problem? I had assumed not, but I'm honestly asking cause I don't know.

Also it should be noted I've discovered many other skin materials this is happening with... including the DeviousDolls-Daphney skin above. This is the one I thought I had found that solved my issue (only to discover it's still present, just less pronounced). It seems all the skin tones I'm shooting for with this character (that I have installed) have this issue. They also all have very similar SSS/Translucency settings to what I posted here.

 

[slitherhence]

Also... looks like this may be

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. Any way to confirm this?

 

[Deleted member 1121028]

Also... looks like this may be

You must be registered to see the links

. Any way to confirm this?

It is, since forever.
When using spectral rendering - SSS transmitted color get bugged (lot of time because of spotlights but not always, try the same scene with just an hdri). Fastest fix is to swap to something near pure white (something like 254/254/254 RGB, never ever go 255 it will broke the SSS), and correct tint via translucency and SSS color. But it's just an exemple.

And always use faithful, natural is even more buggy with spotlights.

 

[slitherhence]

It is, since forever.
When using spectral rendering - SSS transmitted color get bugged (lot of time because of spotlights, try the same scene with just an hdri). Fastest fix is to swap to something near pure white (something like 254/254/254 RGB, never ever go 255 it will broke the SSS), and correct tint via translucency and SSS color. But it's just an exemple.

And always use faithful, natural is even more buggy with spotlights.

Thank you for the advice. I'll keep that in mind. I really hope this doesn't prove to be a constant issue for me. But it is what it is. I may look into exporting from daz to blender and doing my rendering in blender instead if it proves too time consuming.

 

[Deleted member 1121028]

Thank you for the advice. I'll keep that in mind. I really hope this doesn't prove to be a constant issue for me. But it is what it is. I may look into exporting from daz to blender and doing my rendering in blender instead if it proves too time consuming.

You're welcome.
Cycles does not have spectral rendering (sad because it's a fun feature).

You will run into constant problem with spectral rendering with Daz/Iray.
If it's not for pure showcase purpose - I would avoid it (imho).

 

[slitherhence]

You're welcome.
Cycles does not have spectral rendering (sad because it's a fun feature).

You will run into constant problem with spectral rendering with Daz/Iray.
If it's not for pure showcase purpose - I would avoid it (imho).

I'll have to look for skin mats that don't look so bad without spectral. Thanks again for the advice.

 

[mickydoo]

Thanks for your reply.

I didn't want to fix it in post because, since these seams were going to be visible all across the body in almost every single render, it would increase the amount of work needed for each render significantly. The example you give is very fine and might go unnoticed from a distance typical to most scenes... thus requiring post work only when unusually close-up renders make them visible. What I'm seeing are bold, dramatic seams that can be seen even from several meters away. I've already switched to a different skin material from a different character instead, but I'd like to understand the root cause here.

From testing it has something to do with sub-surface sampling. But I haven't been able to change those settings in a way that resolves the issue but doesn't dramatically change the characteristics of the skin material.

Causes problems:
View attachment 1254476

Doesn't:
View attachment 1254475

If you want to remove the redness from the skin it has to do with these colour settings. There is a script you can get called Ultimate Iray Skin Manager which allows you to adjust them all at once.

The one you cannot see in your pic is called Translucency colour with a weight slider, if it is set to over 50, dialling back to can reduce the redness straight away, don't go under 30 though if you can help it, but it also can make it look not quite right.

The SSS colour is designed to catch wasted light. The light goes into the surface and bounces back out, some of it is wasted, this catches it and uses it, pinks being warm blues being cool, changing that to a pastel blue (always think pastels for SSS) will change it but will also make them really pale depending on other factors. If you click on the colour bar you can just dial back the red in it.

The Transmitted colour is the light bouncing out, this can cause weird things, change it to purple and you will probably get a purple character. Mine are usually a tan colour but my other settings differ, what a tan colour will do to yours I don't know.