UDIMs

UDIM is a tile system for UVs. Instead of one 0–1 square, a mesh's islands are spread across several squares, and each square gets its own texture image. Blender's manual: "UDIM which stands for U DIMension is based on a tile system", where "each tile is a different texture in the overall UDIM texture array" (Blender Manual: UDIMs).

#How the tiles are numbered

The first tile, covering U 0–1 and V 0–1, is 1001. "The next tile that gets added will be 1002 and will be placed to the right of the main tile." The array "is ten tiles wide, so tiles 1001 through 1010 are created on the first row", and then "a new row of tiles is started above the main tile" (Blender Manual: UDIMs). So 1011 sits above 1001, at U 0–1, V 1–2.

Texture files carry the tile number in their names. Unreal's pattern is BaseName.####.[format], for example MyTexture.1001.png (Unreal Engine documentation: Streaming Virtual Texturing in Unreal Engine).

#Why use them

A single UV map means "one texture for the entire mesh"; UDIM solves this "by being able to spread UV islands across several different textures" (Blender Manual: UDIMs). You get more total resolution without one enormous image, and you can give different parts different resolutions. In Unreal, "each UDIM image can have a different resolution enabling virtual textures that have non-uniform pixel density" (Unreal Engine documentation: Streaming Virtual Texturing in Unreal Engine).

#Film and games

UDIMs come from film. fxguide reports that the system "was invented by Richard Addison-Wood" at Weta Digital around 2002, during work on The Lord of the Rings: The Two Towers, and that studios such as MPC, DNeg and Weta use it daily (fxguide: UDIM UV mapping). The texture painter Mari also came from Weta and supports UDIM natively (fxguide: UDIM UV mapping).

Games took a different path. The same article notes that "Many games companies use Atlases for texturing", packing an asset's textures into a single 0–1 tile (fxguide: UDIM UV mapping). See texture atlases.

This has been changing. In 2021, Rizom-Lab said its packing rework was driven by the growing use of UDIMs in games (80 Level: Meet RizomUV 2022). Marmoset Toolbag 5 (2024) can "bake and render UDIM materials", and its painting tools work across tile borders (CG Channel: Marmoset releases Toolbag 5.0 in free public…). Houdini's Karma Texture Baker creates one bake setup per tile when the mesh has multiple UDIM tiles (Houdini documentation: Karma Texture Baker LOP).

#Engine support

Unreal Engine supports UDIMs through virtual textures. "When using the UDIM naming convention, UE will import groups of image files as a single Virtual Texture Asset" (Unreal Engine documentation: Streaming Virtual Texturing in Unreal Engine). The importer scans the folder for files with the same base name, and "the four-digit number defines the location where UE should map the image" (Unreal Engine documentation: Streaming Virtual Texturing in Unreal Engine). See virtual texturing.

Substance 3D Painter paints UDIM projects through its UV Tiles feature, which "currently only support[s] the UDIM naming convention". Adobe warns that UV Tile projects "can be demanding" and recommends an SSD (Substance 3D Painter documentation: UV Tiles).

#UDIMs in environment art

• Large hero assets: a statue, a ship, a cliff face or a building facade that needs more resolution than one texture gives.
• Scanned assets from photogrammetry, which often arrive with several high-resolution textures.
• Assets shared with film or cinematics, where the source asset was built with UDIMs.
• Baking to several tiles in Toolbag or Houdini (CG Channel: Marmoset releases Toolbag 5.0 in free public…; Houdini documentation: Karma Texture Baker LOP).

#Common mistakes

• Islands crossing tile borders. Each tile is a separate image, so an island must sit inside one tile.
• Assuming every engine imports UDIMs. Check support before committing; Unreal imports UDIM sets as virtual textures (Unreal Engine documentation: Streaming Virtual Texturing in Unreal Engine).
• Using UDIMs where an atlas or tiling material would do. More tiles mean more files and more memory to manage.

#Related terms

UV mapping · virtual texturing · texel density · texture atlases · UV packing and padding

#Further reading and watching