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Skin Micro Bump

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#1 jeffkingdev   Members   


Posted 21 January 2014 - 02:11 PM



I heard of a technique called micro bump.  I can't find much about it online, but I assume it's something that simulates very tiny bumps on the skin so as the surface won't appear so flat when viewing close.


Look at this screenshot:



Notice his forehead has lines where the spec light shines.  I'm trying to do similar, but I applied a separate bump and the results are not even close.


Any idea how they get those super nice lines\bump across the skin like that?


Thanks in advance.

#2 BarrySkellern   Members   


Posted 21 January 2014 - 05:03 PM


Take a look at the next-gen character rendering material from Jorge Jimenez. http://www.iryoku.com/stare-into-the-future


I think the large download is the slides from GDC 2013 - I read them from a different source originally and don't have time to download the large file to check. But if it's the correct document then it contains a lot of really fascinating stuff about skin and eye rendering, subsurface effects in thin structures (like back-lit earlobes) and so on.

Visit http://www.mugsgames.com

Stroids, a retro style mini-game for Windows PC. http://barryskellern.itch.io/stroids

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#3 jeffkingdev   Members   


Posted 21 January 2014 - 07:53 PM



That's an excellent resource.  Exactly what I was looking for, thanks!

#4 Hodgman   Moderators   


Posted 21 January 2014 - 09:03 PM

Thanks from me too Barry, that's a good link biggrin.png


@jeff, in the screenshot that you showed, they could just be using a really high resolution normal map for each character, instead of a low-res one plus a microbump map.


At one games studio, I spent a week implementing a fancy skin shader that allowed the artists to blend between 4 different micro-bump textures over different parts of the skin... but in the end the texture artist told me that he didn't want to use it, and would rather just be allowed to author 2048x2048 resolution normal maps.


Micro-bump is bascially just sampling a second normal map (tiled repeatedly) and "adding" it somehow to your main normal map. There's lots of ways to combine the two, which greatly affects the results.

Last time I implemented it, I used the "Partial Derivative Normal Maps" technique from the link below, which allows you to add two "partial derivative normal maps" together and then renormalize them, and get a sensible normal as a result:



These aren't about microbump, but some older links on skin shading:



Edited by Hodgman, 21 January 2014 - 09:07 PM.

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