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stevijn

Hair Banding

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Hi guys, 

 

i'm generating these large patches of hair but i'm experiencing a banding effect, see attached. 

 

Any idea where this might come from and how to get rid of it? i've tried everything

 

Your help would be much appreciated, thanks in advance!

 

Stevijn van Olst

Screen_Shot_2019-03-24_at_12_50_35.png

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You will need to upload the scene file... otherwise we're just firing shots in the dark...

 

CBR

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  • Hi CBR, 

     

    sure thing, here's the scene file

     

    //S

    scene.zip

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    Interesting. It's only there when shadows are turned on with your lights. I tried all sorts of different settings there, and still the banding.

    I have to go out now, but will do further tests when I get back if the other guys don't beat me to it :)

     

    CBR

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  • Great thanks CBR! I have it reoccurring in all my scenes. I tried different lighting setups, but all lights seem to create this effect to a degree. Maybe it's a setting in the hair/hair texture that can render it more smoothly? I'm purposely not generating geometry on the hair to keep things light, but it seems to add artefacts here & there. Like banding in the black hair gradients in this example as well. I noticed global illumination gets rid of this problem in particular, but would be great if i could avoid it. Also if there's anybody with tips out there to increase the realism without adding geometry/displacement to the hairs that would be super awesome. Thanks again!

    Screen Shot 2019-03-24 at 16.44.15.png

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    I have been doing further tests. Not finding anything I'd call conclusive, but I would say it's there even with GI, so I think the problem is in the hair somewhere. I think it's something to do with the sheer amount of hairs and the fact that so many of them intersect each other. If we turn down the end thickness of the hair to something like 0.2 the problem disappears because (if my theory is right) nothing is intersecting there anymore. Don't think I'm seeing any banding in this ?

     

    noBanding.thumb.jpg.4ee2faeab2a509cbd6bd710cb2c9fe40.jpg

     

    So, that seems to be one solution, although of course it may not be the one you want. The other way to address this (again, if my theory holds water) would be to lessen the amount of hairs, whilst keeping start and end thickness as you had them. Here I culled about half the hairs you had going on in all 3 types...

     

    338299800_noBandinglesshair.thumb.jpg.c63860a130369a17413afba929ef87a7.jpg

     

    Again, not seeing the banding so that seems to have also worked.

    So, that's my evidence - don't know how correct the theory is, but at least you have things to try...

     

    Let us know how you get on, upload a result you are fairly happy with, then we can work on adding realism...

     

    CBR

     

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  • Thanks for the quick reply CBR! I've reduced the amount of hairs to a minimum( while still keeping it dense enough to feel like a rug) - There's still some banding though (more noticeable in zoomed out view), but it's definitely less. This does tell me that maybe density is not the core of the problem? I'm curious what you think i could do to improve realism on the individual strands and overall scene! i've been struggling with this thing for a while :)  

    scene2.zip

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    So what are we trying to make here ? Standard wool carpet ? Or some other type ? Have you got any reference photos that show the sort of thing we're aiming for ?

    If it is the woollen type, then I think the mistake we're making is to use one thick 'hair' per clump, rather than lots of smaller hairs clumped into your larger groups, which i think will just give a more carpet-like effect. I'll have a play with that later when I can see what we're trying to match...

     

    CBR

     

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  • It would be something along the lines of this reference (attached), which is why i was using the thicker strands. Everything i've tried so far to add more detail/fuzz ends up in massive render times. Especially when zooming out to show more of the design, with more strands+fuzz things get heavy very fast. Would hugely appreciate any type of pointers in the right direction! 

    Screen Shot 2019-03-24 at 21.16.06.png

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    The trouble is that the hair system was designed to make stuff look realistic when the camera is a certain distance away from it. What you are wanting is something much more close-up, which is, at the end of the day going to involve a lot more detail, and although Cinema is probably up to it, wherever there is additional detail, you will be paying the price in render times. Here's some tests that illustrate the issue.

     

    I can make pretty decent carpet from a distance with just 1 hair system (here based on your reference rather than the red stuff)...

     

    Distant.thumb.jpg.8015b8929936c3a78720bd005240a42b.jpg

     

    Nothin special, but it kind of passes. And if we add another layer of much finer, frizzier, kinkier hair, then that all starts to look quite convincing...

     

    Distant2.thumb.jpg.7caacf37927f741166af1463c99e8ae7.jpg

     

     But if we zoom in to the sort of scales you're talking about viewing it, it no longer looks much like your reference image.

     

    close1.thumb.jpg.e7742e0a971d6e9ca13bd373b659c7b5.jpg

     

    We've lost all that fuzzy feel and what looked quite detailed from a distance is now not much more than painterly blobs, and the word carpet doesn't really apply ! :/

     

    Ok, so let's add in and dial up (by which I mean massively increase the numbers of) the fuzz layer, which should improve things a bit...

     

    close2.thumb.jpg.d94ffac924aca1d0376a75631e13906a.jpg 

     

    ...and yes it does - it's certainly better than without it, there's a lot more detail, and we are starting to get more of a carpet-y feeling back.

    Is this level of detail good enough for your purposes, or do we need to look at the microstructure of actual carpet, which looks like this...


    videoblocks-close-up-of-beige-carpet-fabric-pattern-macro-texture-background_rbi2tm7f4_thumbnail-full01.thumb.png.303002d07555fdecb46a4457107c6ce5.png

     

    Once we get down to this sort of scale, the whole structure changes and we can see that each 'hair' is actually a somewhat flattened collection of tufts of much finer hair. I think it will take some serious effort to get this sort of look with Cinema's hair system, though maybe if you have hours and hours to throw at it you can get close. Render times will be sky high even if you can persuade it to look like this, but we just have to accept that if we want the detail - nothing in Cinema is gonna render faster than hair, so this remains the best way to do it if it can get the result you want.

     

    One tip about how to iterate through your tests - I would start in a new file on a really miniscule plane, and only try and make one tiny area of it - that way your render times won't infuriate you as you find the right combo of settings... literally try and make just 3 or 4 tufts initially - and I think clumping and curling, and a separate frizz layer as above are going to be things to try first..

    I don't know how helpful this has been, but you might be able to work with the double hair technique to get something passable...

    I wish you the best of luck and do show us what you end up with... if I make any progress I will also post it here.

    CBR

     

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    I should have gone to bed, but remained upright long enough to try some proper macro-level carpet as per the plan above...

    This is still a long way off how good it could be, but I reckon it's more what that looks like at this sort of magnification.

     

    513811391_microcarpet1.thumb.jpg.4636bcf9e9d738317f9df4c8f9cfdcdd.jpg

     

    Slightly too tufty, and whilst we're chilling that out, now we can try your red colour - here perhaps the medium variant...

     

    1823342509_microcarpet2.thumb.jpg.a3dc50b5c37228758281a3c0d216e955.jpg

     

    Again not perfect, but hopefully you can see how we can begin to work this round to being more what you want...

    We are treading a slightly fine line between what looks like carpet and what looks like fur, but we certainly can't say we are lacking detail anymore...

     

    However, by chilling out the clumping (making less hairs do it) we've been able to do this with only 1 hair system and 20,000 hairs which isn't too bad. From these tests we can see that for the sort of area you need the camera to cover in your final shot, you can probably do this in about 2 million. It's gonna take a while, but not ridiculous.

     

    Here's the scene file for that if it helps...

     

    Macro Hair 02.c4d

     

    CBR

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  • Wow thanks for all the extensive examples and explanation CBR, i really appreciate it! it's very helpful for me to get these insights into the hair system and how it behaves. I now realise the limitations and am able to finish the project with this knowledge in mind. You're a lifesaver, and im super grateful. Cheers!

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