Time and time again I have to keep telling people to resize their textures, its one of the things I messed up when I was new and its one of the things no one is told but its almost as bad as making all your brushes structural, maybe not as serious but the outcome can be ugly, as you will soon see.
Textures are measured in powers of 2, with 16x16 pixels being the smallest texture with any probable use, most textures will be larger. Textures do not have to be square, just as long as both dimensions are powers of 2. Powers of 2 include 2,4,8,16,32,64,128,256,512,1024 and 2048(if you dare) examples include: 512x256, 1024x64, 256x64.
This doesn't matter what kind of texture it is, it applys to everything, including; skybox/minimap/levelshot/texture/RoQ video its any texture that will be used by the engine.

You might ask yourself whats the point of resizing my awesome textures? they look fine... well theres where you wrong, textures that are not powers of 2 will be rounded down to the nearest power of 2.
This could mean a huge deal if all your textures were 1 pixel off a power of 2, then your textures will be halved in quality. If you don't believe me I have resized all the textures to 5pixels less across each dimention, seen in this view of ut4_casa as an example, observe.

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Copyright © 2009 Steven "Delirium" Krzanich. This document is released under the terms of the Creative Commons Attribution-Share Alike 3.0 Unported License, http://creativecommons.org/licenses/by-sa/3.0/