Skin Texturing and Shading in Maya Part 2

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1 Skin Texturing and Shading in Maya Part 2 In part 1, I gave an overview of Mental Ray's skin shader. In this chapter, I'll be discussing some of the techniques I've used to make texture maps in the past. My goal isn't so much to create realistic textures, but to break up the colors and highlights so the character doesn't look like it's made of plastic. Procedural Maps Probably the most difficult part texturing, especially for a full-body mesh, is the resolution of the map. Suppose you create a 2048x2048 map. In most cases, this should be enough... but what if you decide to do an extreme close-up of any particular part area? If your textures were painted by hand or sourced from photographs, the best thing would be to create a very high resolution master file. This texture would be too impractical to use all the time, so you might either divide it into sections, or only use the section that is visible in the close-up. Another option would be to use a mixture of procedural textures. Since these are generated by Maya, they take up very little memory and are resolution-independent. For skin, I like to use three in particular - Leather, Solid Fractal, and Volume Noise. Leather is most useful for creating a very fine, cellular-looking bump map. A map doesn't need to cover the entire UV range.

2 Solid Fractal can be used to vary the color of either your epidermal or subdermal skin maps. Using different settings, Volume Noise can be used to create freckles and pores. Once you find the right settings, these maps can be baked to images, so you can edit and combine them in Photoshop. In some cases, like the leather map, you may not only want to bake out a very high-res map, but you may also need to bake it out in sections. At least with the 32-bit version, Maya tends to run out of memory when rendering very large maps. Painted areas and color masks Not everything can or should be done with procedural maps. I like to use Maya's 3D Paint tool to create simple black & white masks. Additional masks can also be created by applying clusters or smooth-skinning to a higher-resolution mesh, and and saving out the weight maps. The only real advantage to using clusters/skin instead of the paint tool, is if you want a mask that precisely follows specific edge loops.

3 In Photoshop, I prefer to use Solid-Colors instead of normal layers. The main reason is that, since Solid-Colors are just a color code and a mask, they take up less memory. You can also change the color of the layer at any time. Each layer may use a different blending mode some are screened, some multiply, others burn or overlay... whatever gives the best results. Alternatively, if you'd like to keep your maps procedural, you could simply combine up to 4 painted masks into a single image, and have Maya use the individual channels as masks for the procedural maps. The only potential downside to this, is that your shading network could become very dense and difficult to keep track of.

4 Pre-lighting - Global Illumination One additional layer that can be useful, is a global illumination light map. Now, actual GI can be fairly slow, so you might be better off faking it with a dome-light rig, such as Seth Hall's Illuminati.

5 Roughing It Up If we look at the skin shader without any maps, you can see that it looks rather smooth. With real skin, the highlights are broken up by the pores, wrinkles, and all the tiny cracks. Applying a leather map to the overall specular weight breaks up the highlights, but the surface still looks smoother than it should. Plastic! Still not quite right... Connecting the same map to the bump channel helps break up the light further.

6 In this image, I've applied another, larger leather map to the subdermal color. With only a small variation in the color, it can add some subtle detail underneath the surface - That's all for this chapter. In the next one, I'll be exploring some of the techniques used to create more realistic textures from photographs.