Skin Bump Reflection Texture

Monika KubickovaSkin ReflectionMrvine GracelSkin Bump Map

O step 11: High-frequency bump u, nnant The rtnwnside here is that this can also introduce noise as we du<sh th.

We have two problems with taking just the luminance or blue component- ine o f photographs. For that reason, I have included a we have low-frequency and pigmentation inform*i ion mixe n as, wej pro »s "fli m ^ ^ ^ how much-

Let's tackle the low-frequency information first-it s the eas s prob em re ionsp ^ t0 remove Here is a C|QS ™<J

to solve. The methods that apply bump mapping a des gned as thHowrreq y remQva| Qf 6g% ^ b cheat for rendering medium small-scale surface «na6°ns^ DirectX shader tool provides black-point, exposure, and gamma contra detail bigger than micro bumps that influence dittos ec ar a tenstics J £ m The een and re(j areas »¿«J*

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Q Step 12: Better bumps

The next problem is pigmentation in the skin—things like moles and freckles. Left alone they will cause big dips in your render. They shouldn't be in the bump map at all unless they are due to huge pocks in the skin' Fortunately, these are features that are dark in all the color channels and we can use a red/blue ratio to suppress them. Here is a close-up of Monika's left cheek where a freckle has almost been completely suppressed by this method.

Monika Kubickova

O Step 13: Specular maps

Strictly speaking, the specular map should be just a fairly soft map that indicates where the skin is more or less reflective. However, because of the way many of the skin shaders work, you often get a more realistic looking render if you give a more detailed specular map—something that looks more like a blend of bump and specular. Here, we see a specular map that is created from the formulae 2b-g. In future, I will extract specular, along with diffuse and sub-surface components directly in the DirectX shader so that the result matches the photograph using your target render shader. _

Model Portrait HeadSkin Specular Reflection

O Step 14: Specular color

It can add realism to many skin shaders if you can specify the color tint of the specular color. The specular map generator in the DirectX shader tool gives you the option of winding up an approximation of the specular color. This is the full blended color minus increasing amounts of green and red as they penetrate the skin and are reduced in the specular component Thus the specular color map looks very cool compared to diffuse color and original photographs.

O Step 15: Sub-surtace color

As you go deeper into the skin, more of the short wavelengths are lost. By modeling the loss as increasing logarithmic falloff of intensity with depth, you can generate maps that show you color at different depths. I have added a sub-surface map generator to the DirectX map shader tool that lets you go from the surface to a maximum depth. As you go down, the light goes from neutral, through yellow (red and green), to deep red You can see different sub-surface features appearing at different depths.

Joseph Polevoi
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