PNG vs DDS 그것이 문제로다..

* http://www.libpng.org/pub/png/
* DXT Wikipedia
* GPU DXT Decompression
* DXTC: DXTC Examples and Technical Comparison 
* Unreal Texturing Guide
* http://developer.nvidia.com/object/texture_tools.html

Caution: a hardware bug in some nVidia chipsets, including the NV20 (GeForce3/Xbox), potentially makes certain DXT1 textures exhibit banding/ quantization artifacts. Specifically, decompression is performed in 16-bit color mode internally, making the resulting texture potentially unacceptable for use, especially when combined with other operations. This problem has been corrected in the NV25 chipset and all other DXTC formats on nVidia hardware are okay, as textures are decompressed in 32-bit color internally.

Eight-bit Palettized

P8 textures, as they are denoted in the editor, are the same 8-bit palettized (256 color) textures used in the build 436 engine and earlier ("Unreal" and "Unreal Tournament" timeframe). Even though they are uploaded to the video card as a full 32-bit RGBA texture, when properly quantized a P8 can look identical to the original 24-bit source art, while still offering a 75% savings in disk and system memory.

P8 textures offer 1-bit alpha in the form of a mask color. If a texture is imported as masked, color index 0 is set as transparent. Once you palettize your texture, you'll need to edit your 256-color image and apply color zero to the transparent portions of the texture.

Recommendation

Use DXT1 textures as much as is possible. While artists need to examine DXT1 versions of their textures due to the penetration of nVidia hardware with the decompression bug, the greatest space savings can be had with them.

If watching for rendering artifacts is not an option, DXT5 supports the most flexible alpha channels, while not increasing memory usage beyond that of a normal 8-bit palettized texture.

Also, if you need full color resolution for a texture, without an alpha channel, use an 8-bit palettized texture. While requiring the same amount of video memory, disk and system memory usage is a mere 25% of full RGBA, and the differences are undetectable in most cases. Use full RGBA only when DXT3/5 do not suffice in the both the color and alpha quality department, in highly visible expanses, such as skies.