Cotton Shirt Advice Needed

[thebeals]

Hey all,

I am working on attempting to create a photo-realistic shirt in vray 3.1. I've noticed that cloth has SSS attributes and does a decent amount of scattering, so I have been using the fastSS2 shader. It works great, until I add displacement and then my render times jump exponentially. I even have my displacement subdivs kept very low at 2 and the displacement sampling process is actually quite fast, it's just all of the material sampling. I've tried turning off a bunch of stuff to keep the render times down, but nothing really helps. My light setup is a simple, 2 area lights and a dome light.

I've tried using a standard material piped into a 2-sided material to fake the light passing through, but it doesn't look good at all, and gets too dark.
I've also tried using a standard material with refraction and translucency via the wax mode and it brings me closer, but still not satisfying.

I should also mention that I'm faking the retro-reflectivity/asperity on the edges with a falloff node and using the ggx brdf with glossiness of .2 and a tail falloff of 1.

What are your guy's solutions and advice of what to do/how to create a realistic cloth/shirt material? Do you use SSS? I've checked out Lukas' post on Crossing The Uncanney Balley and it looks like he agrees there is SSS in cloth, but he only fakes it in post, but he does mention there could be a specific cloth material coming soon from ChaosGroup.

Thoughts? Thanks for any and all direction!

[Zdravko.Keremidchiev]

There are quite a lot of fabric materials. It might be helpful if you could attach some reference images (with explanations) of the exact kind of fabric that you want to create.
It will be easier for the forum users to give suggestions.

[thebeals]

Certainly,

Here are some examples of fabric materials that I have not been able to achieve yet:

Thin Fabric:


Two-Sided material would probably work for this, but there is also a decent amount of sss, how would you achieve this type material?

T-Shirt:

Two-Sided material could work for this, but it seems to darken too much. The Two-sided material seems only really applicable to paper, but I could be wrong. There is still a lot of light transportation happening through the fabric. How would you achieve that affect?

Wool/knit fabric:


There is tons of SSS in here, but using fastss2 takes too long with this amount of geometry. Would you use sss, or fake it with translucency with the Standard material, or would you maybe try to do some sort of volume shading instead? 've even been tempted to fully simulate this with curves and individual hair fibers with hairMaterial, but that would be pretty extreme

Thanks for any help! I really appreciate the direction and help. It would be great to be able to understand how to create photo realistic fabrics.

[Mokiki]

Definitely interesting topic. I rarely do fabrics and the times I do I always struggle with them.
I'm currently having a go at the "Wool/knit" fabric because I don't have any solid textures for the cotton at hand.
With wool I'm not sure if you really need any translucency I have the feeling that you can get pretty far alone with some good reflection values and a solid displacement map.

Here is example of what I managed to do during lunch. (Sorry the model wasn't made for that kind of displacement so it might look a bit odd)
Overall its still a little bit flat and liveless but I'm pretty sure with a bit more tweaking and some better maps (not the hackjob I did :P) this could be solved.

Right now I'm just using a Vraymatl with a solid color / mid-low reflection values and rglossiness of 0.3 and ggx with a tailfalloff 0,9 / a strong bumpmap and displacement. And vray fur added (no hair material just the same as the fabric. Might do some test later with hair mat.)

*edit* rerendering image just noticed a mistake
*edit2* added image again (sorry)

[thebeals]

Thanks Oliver!

This is awesome! yea I have the exact same problems that you have had. Iv'e always struggled with this. Below is what I've been able to get with wool/knit, and it's on par with what you're getting. But there is still definitely something missing... maybe it's just better textures... But I feel like I am missing a bit of glow and color bleed that you get with SSS. I've even been tempted to do a wool pattern using micromesh in Zbrush and decimating it and just bringing it into Max to get a truly accurate-geometry wise-model.. But who knows what that would do to render times.. I also try to layer different textrues and bercon maps, but my render times just keep going higher. For this small render, it took nearly half an hour on a pretty solid i-7 machine with 16 gigs of RAM!! The displacement just kills the render times. Without displacement, the render times are only 2 minutes! Am I doing something wrong with displacement? I only have the displacement subdivs at 2-not even close to the insane default of 256.

My render stats are:

1/6 subdivs with .05 color threshold (In production my threshold is usually around .015, but if I did that for this, my render times would have been 2 hours!!)
.85 adaptive
.015 noise threshold

64 samples in reflections
100 samples in two lights and an hdri dome.



Other than the obvious tiling of pattern, there still seems to be something wrong. It looks good... just not photo-realistic. I don't have hair on it, like you do, so I am sure that will help, but I don't think that is the only reason this doesn't look realistic.

For that retro reflection/asperity at edges, I've done something kinda cool.. I don't know if it's right, but it my mind it sounds good-although it does eat up a lot of render time.

I have taken a falloff map and changed it to shadow/light and than masked that by another falloff that is the typical perpendicular/parallel. That way the fuzz doesn't appear in shadow areas, or where there is no light direction. Kind of like masking it by ao, but more accurate.

Let me know your thoughts!

[Mokiki]

Tip for displacement if you are using 3d displacement (which I did in my case) enable "static geometry". This will as far as I understand precalculate the displacement and store it onto memory. You will use more ram but the rendering takes a lot less time. I think my render took around 11 minutes (1341x1500px) on 1 i7 machine ( 8 threads 4ghz).

You are right about the color bleeding and that is still an issue I try to solve. But I still try to avoid sss in my current tests for one because my geometry is flat (sure I could use a shell modifier but I'm stubborn :P)
What I'm currently doing to break up the pattern is using a few noise/grunge maps multiplied onto my displacement map in my reflection slot to darken to the gaps betweent the knit pattern a bit and break up the reflections.
Additionally I also multiplied/screened some noise/grunge maps onto my displacement to give some irregularity to the whole thing. Which my rendertimes didn't like that much even with low AA. But I think its getting there.

Sorry for making this post a bit short but currently have some other stuff to deal with. Will definitely revisit this tomorrow or on the weekend.