はじめに

The UV Editor is used for editing UV maps, which describe how a 2D image should be mapped onto a 3D object.

../../_images/editors_uv_introduction_main.png

UV マップとテストグリッドテクスチャを持つ UV Editor(UVエディター)。

Image textures are typically needed when the desired look is hard to achieve with procedural textures, or if the texture is not uniform. For example, a car would only have scratches in a few places where they make sense, not in random places all over its body.

Blender offers a number of projections (Box, Sphere...) that automatically apply a 2D image to a 3D object, but these tend to only work for simple meshes. For more complex ones, you need to create a UV map instead. This is a flat area where each face of the 3D object is laid out on the 2D image, specifying which part of the image it should be textured with. This gives you complete control over the mapping process.

The name "UV" refers to the axes of the map: U for horizontal, V for vertical. These letters were chosen to avoid confusion with "X" and "Y", which refer to axes in 3D space instead.

UV の説明

The best analogy to understand UV mapping is cutting up a cardboard box. If you were to take a pair of scissors and cut along its edges, you would be able to spread it out flat on a tabletop. As you are looking down at the table, we could say that U is the left-right direction, and V is the up-down direction.

As a next step, you could put the spread-out box on top of a poster, cut the poster to match its shape, glue the poster to the box, and finally reassemble the box. You now have a 3D box textured with a 2D image.

A UV map describes how the box is cut up, and how it's laid out on the poster. You have complete freedom in how to do this: if you wanted to, you could cut each individual side of the box and position, rotate, scale, and even skew it on the poster independently of the other sides.

例

../../_images/editors_uv_introduction_3d-uv-space.png

3D 空間 (XYZ)と UV 空間。

In the above image, a dome in 3D space is flattened into a disc in UV space. Each 3D face is then textured with the part of the image it covers in the UV map.

The image also demonstrates a common problem in UV maps: distortion. Notice how, even though the checkered squares in the 2D texture are all the same size, they get different sizes when applied to the 3D dome (they're smaller at the base than at the top). This is because the faces in the UV map have different relative sizes than in 3D space, which is a result of the flattening process.

You'll typically want to minimize this distortion by manually guiding and tweaking the flattening, using seams for example. However, it's not always possible to eliminate it completely.

Interface(インターフェイス)