S3TC/DXT/DDS Texture Compression

Posted: Jan 12, 2016 in Editing, Tools

What is the benefit of using compressed textures, and which should I use ?
Are they standard and will they break anything ?

S3TC = S3 Texture Compression
DXT = DirectX Texture
DDS = Direct Draw Surface – (File extension eg. utxtest.dds)
DXT1 http://wikipedia.org/wiki/S3_Texture_Compression#DXT1
DXT3 http://wikipedia.org/wiki/S3_Texture_Compression#DXT2_and_DXT3
DXT5 http://wikipedia.org/wiki/S3_Texture_Compression#DXT4_and_DXT5

It has been standard since DirectX 6.0 and OpenGL 1.3 (via the GL_EXT_texture_compression_s3tc extension)
Unreal came with DirectX 7 support.

S3TC/DXT/DDS Usage notes:
Non-compressed will be 8bit – 256 colours
Compressed will be 24 bit – 16,777,216 colours
Compressed transparent images are 32 bit including alpha channel
Since the newer DX8+ renderers, Hi-res and compressed are not inclusive. You can make large non-compressed textures, but it is not wise.

The biggest advantage of using S3TC/DDS textures is that you are not forced to use 8bit 256 colour-mapped images.
You can prepare a full colour photo, or a transparent 24bit PNG or TIFF as a DDS in GIMP or Photoshop etc. and have the textures at the original full photo-real quality.

Do not use compression or mipmaps for interface/HUD images or map screenshots.

Use DX1 for normal textures with no transparency. You will get the best compression ratio.
Generally DXT3 is best suited to images with sharp alpha transitions, between transparent and solid areas.
Because DXT5 uses an interpolated alpha scheme, it generally produces superior results for alpha (transparency) gradients than DXT3.

Over the years I found it best to keep 2 installs.
1 clean and raw for editing, and another for playing and adding mods to.
This means I can happily edit with v436 and standard textures, and play with v451 and hi-res textures.

The replacement textures do not compare to the two broken ones on CD2, so anything said about experience with broken textures can be ignored if you aren’t using them.
Simply ignoring the textures on CD2 and using the UTTexture packs instead will avoid any problems, and keeps things simple.

NOTES: Correctly made textures should have both standard and compressed “DXmerged” in the file. This means users only have to enable/disable the setting, and can use the same packs.

Traditionally, mappers were told not to use compressed textures for editing because they would not display in UEd.
Since the newer video renderers became available, this is no longer a problem and they will display.

This still leaves the issue of larger textures, where there is the possibility of miss-alignment if they are not perfect.
Depending on the map you may not notice any problems, and it will never break a map.

Then you have maps that are made with compressed hi-res textures (eg. CTF-Face-Palm).
There is no option. You either enable S3TC support or don’t play it.

My Google Drive – S3TC/DXT/DDS Tools and plugins collection

S3TC And Mapping Guide  –  Merge DXT scripts


NVIDIA Texture Tools for Adobe Photoshop
GPU Accelerated Texture Compression
nVidia Legacy Texture Tools
Free multi-OS image editor http://www.gimp.org
S3TC/DDS/DXT plugin for GIMP http://code.google.com/p/gimp-dds/


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