テクスチャマッピング
Texture maps allow assigning color or material to a surface or a volume, borrowing from the idea of Texture mapping in graphics. The element is first used to associate a with particular texture data. The data can be represented as either a 2D or a 3D array, depending on whether the color or material need to be mapped to a surface or a volume. The data is represented as a string of bytes in Base64 encoding, one byte per pixel specifying the grayscale level in the 0-255 range.