cell skins

by NM-8 in Materials, Shaders, Textures

cell skins node for cycles

cell skins is a node and some shader examples that replicate the cell structure of skin procedurally. from human skin to reptile scales, for dinosaurs and dragons this node can be used whenever a creature is shaded.


-procedural means no texture-resolution-issues.
-it stretches according to the surfaces curvature, to achieve an organic impression.
-a humanskin-shader and a reptile shader are included as an example on how to use the node.


Why should you use this node:

skincells are hard to create with cycles nodes. doing skinbump by texture and sculpting takes a lot of time.
there are cellbased fractals in cycles (the voronoi map), but it creates more of a bubble-like pattern, which is not satisfying for skin purposes.
this node creates a cell pattern with a few clicks. So its very helpful if you work with lots of characters, but dont want to spent too much time for texturing.
the node itself outputs a greyscale texture which could be understood as the heightmap of the cells. therefore you can use it as input for gradientramps of mixColor nodes to color the cells, or as height input for a bump-node.
in the reptile shader you get 3 color inpupts, which define the top, edge and gap color. they can be linked to a lowres texture or any other nodes, for further details.

the size of the cells is not static but grows and shrinks with the curvature of the surface, which makes an organic impression.

how to use the shaders or node:
append it from the file cellskins.blend (file/append/...goto file... /materials/...choose the material you want.

adjust the parameters of the shaders or node:

reptile-colors: the top/edge/gap color of the cells (advanced users choose textures as input here)
the humanskin just has one color channel (to input an imagetexture here)

scale: the scale of the pattern (higher values make smaller cells)
stretch: how much shall the surfaces curvature influence the pattern of cells

The stretch factor changes the cellstructure depending on the pointiness of the surface.
Pointiness then varies between scale*(100% + 0.5*stretch%) and scale*(100% - 0.5*stretch%)
 therefore in areas where pointiness changes much, squeezing occurs.
 while in other areas where pointiness is constant it will look unstretched and has a certain scale.

noise: how noisy the cells are.
bump: the bumpstrength of the cells.
contrast: how sudden curvature changes scale of the cells. this parameter is in reptile material and humanskin material.
offset (for advanced use): define the mean curvature of your model to the shader. 

a creature usually needs negative value between 0% and -50% (as it is a closed surface, hence a convex surface) a flat plane or landscape would use =0% offset, as its mainly flat. and a concave model could use positive offset. but this really depends on the characteristics and also on the details of your model, and what you wnat to achieve. so just play with this setting, and look whats best for you. :)

If you use the shaders for animation, be sure to input a UVMap into the Vector Input of the shaders or the node. Otherwise the cellpattern may flow along the surface, as the model moves. Preceed as you would with fractal-textures.

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