DXT Texture Compression

[stolenrays]

I was wondering what other modders use for the compression of their .dds textures. I've been using DXT3, but recently read that DXT5 should be just as good, if not better.

Anybody recommend switching to DXT5, the compression size could help.

 

[tesb]

dxt1 if you have no alpha layer
no mipmaps for assets that don't change in depth, i.e. 2d pictures
dxt 5 else. the difference between dxt3 and 5 is just a slightly better alpha layer afaik the size are nearly the same.

 

[Refar]

What tesb said. The compression rate is the same for all dds formats. The only difference is how alpha is handled - whereby dxt5 allows for smoother transitions, while dxt3 is more precise on hard edges. Thus dxt3 is usually better for civ4, since we are often using small size textures with sharp on/off alpha rather than smooth gradients.

 

[tesb]

as an addendum: if you want a sharp alpha layer you can still use dxt5 and use a high threshold in the Nialpha property.

 

[stolenrays]

Thanks for all the information. I've found that when I go from dxt3 to dxt5 I get a 75% reduction in dds file size (e.g., 256k to 65k). That's pretty significant in my opinion.

 

[tesb]

what program are you using? for me dxt3 has the same reduction as dxt5 using either gimp or the DXT1 bitmap manipulator. a 75% reduction is more akin to dxt1 where there is no alpha layer.
edit: or maybe the resolution has changed during the dxt5 save?

can you please attach both versions of the texture?

 

[Refar]

You must be somehow mistaken - maybe your software has export profiles that resize your image without you noticing. Or it might be just a screwy exporter plugin (dds could in theory be a container for uncompressed bitmap as well).

For me a 256x256 texture (which is only ~200k as bitmap in the first place) compresses to 65k (with no mip-maps) with both Dxt5 and Dxt3. A Square 512 texture goes from ~750K down to 256K.
Also the format specification is telling us that dxt1, 3 and 5 are using exactly the same fixed bitrate encoding (apart from alpha).

But there is no harm in using dxt5 over dxt3 either, so just choose what works best for you.

 

[stolenrays]

Here, check out these textures, one is dxt3 and the other is dxt5.

 

[Refar]

The dxt3 one with 192kb is exactly what a 24bpp bitmap of the same size would take - in other words it's not compressed at all.
It looks i like your exporter is just a bit screwy when it comes to dxt3. The dxt5 one is fine however.