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The Basics of UV Mapping

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This tutorial covers the basics of texture unwrapping, otherwise known as UV mapping, the process of wrapping a 2d texture image onto a 3d object. 


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What is Surfacing?

By default, a recently finished 3D model is a lot like a blank canvas—most software packages will display it as an evenly lit, neutral shade of gray. No reflections, no color, no textures. Just plain old, boring gray.

Obviously, this isn't the way the model ultimately appears in the final render, so how is it that a model goes from an uninteresting shade of gray to the fully detailed characters and environments we see in movies and games?

Surfacing, which includes UV Layouts, texture mapping, and shader building, is the overall process of adding detail to the surface of a 3D object.

The job of a texturing or shader specialist may sound somewhat less glamorous than than that of a modeler or animator, but they're equally instrumental in the process of bringing a 3D film or game to fruition.

Try to imagine Rango without his colorful, scaly skin. Or Wall-E without his fantastically weathered-and-worn paint job. Without a good team of texture painters and shader writers any CG production will ultimately look flat and unconvincing.

Shading and texturing may be two sides of the same coin, but they're still fundamentally different processes, each deserving its own discussion. In this first section, we'll discuss UV layouts, and everything that goes along with creating them. In part-two we'll return with an explanation of texture-mapping, and then we'll round out the series with a quick look at shader networks.

Unwrapping a Model and Creating a UV Layout

Texture mapping, invented by Ed Catmull in 1974, is one of the more ingenious breakthroughs in the history of computer graphics. To put things in very general terms, texture mapping is the process of adding color (or other information) to a 3D model by projecting a two-dimensional image onto its surface.

However, in order to apply a texture map to the surface of a model, it first needs to be unwrapped and given a functional UV layout for texture artists to work with.

    A UV layout is a visual representation of a 3D model flattened onto a two dimensional plane. Each point on the two-dimensional plane is called a UV and represents a vertex on the 3D object. In this way, all areas within the boundary of the UV layout correspond to a specific spot on the model. An easy way to visualize what a UV layout looks like is this:

    Have you ever made a cube out of paper? If so, think about the shape you needed to cut into the paper in order for it to properly fold into a cube—it probably looked like a cross, four units (faces) high and three across. If that paper cube were a 3D model, every fold would be an edge, every corner would be a vertex, and every flat area would be a face. Unwrapping a model is very similar, except there are usually more than six faces to flatten.
    Unwrapping: Unwrapping is the process of assigning each polygonal face a set of UV coordinates on the two-dimensional image plane. UV coordinates are layed out visually and exported as a square bitmap image with a resolution anywhere from 512 x 512 all the way up to 6000 pixels by 6000. The artist who paints or creates the texture maps for the model will eventually use the layout for guidance when creating the texture files.

- And that's it! Once the model is unwrapped, the process is placed into the hands of texture painters who will develop detailed image maps on top of the finished UV layout.

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