Common Texture Mistakes

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I've noticed certain mistakes are made by a lot of new or even experienced texture artists, so I thought I'd list them here in the hopes that it might prove helpful.

--Gildoran 22:18, 24 August 2006 (CDT)

Not using exponent-of-2 image dimensions 
Any images used by your textures need to have dimensions that are of the form 2^x since those are the only sizes that graphics cards can accept.
Such sizes include: 1, 2, 4, 8, 16, 32, 64, 128, 256, 512, 1024, 2048, 4096, etc
If an image has a weird size like 300x100, D3 will resize it down to the nearest exponent of 2 (300x100 would become 256x64) resulting in lost image quality.
Lighting baked into the diffusemap 
One of D3's big advantages is its fully-dynamic lighting with bumpmapping and specular highlights... a texture that properly uses these features can look very realistic, especially since its lighting always matches the situation it is used in. Unfortunately, gone are the days of just taking a photo and making it tilable; care must be taken to ensure that the lighting information comes from the normalmap rather than the diffusemap. The diffusemap must not be lit from any one direction, or it interferes with the normalmapping, causing the texture to look ugly when lit from new directions. Taking photos on cloudy days helps. Photos of walls are particularly problematic, since they're often lit from above by the sky. If you can flip your photo in any direction without the direction of the light appearing to change, it probably has good lighting.

See Remove Shadows in Source Images for tricks on how to get rid of baked light from photo resources.

Having apparent repetitions 
The human brain is very good at finding patterns. Unfortunately, this makes it very easy to notice a tiled texture, ruining suspension of disbelief for things like cobble floors, irregular stone walls and dirt. Often the difference between a mediocre texture and a great one is how well it tiles without being noticed. Special/interesting features that stand out tend to draw a player's attention towards the fact that the texture is repeating. Slightly monotonous textures, on the other hand, often have their repetition go unnoticed. It may be a good idea to leave features to things like decals and models.
Using an unnecessary specular map 

Specular maps make things look shiny, and should only be used for metal, wet or highly polished surfaces. Adding specular maps to textures that don't need them (like most wood textures) makes them look vaguely plastic. Use specular maps rarely, and keep them subtle.