Differences between DDS filetypes
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SlipperyJim
Cutthroat
Posts: 427
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 Posted: Mon Sep 19, 2005 2:05 pm Post subject: Differences between DDS filetypes |
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When saving a DDS file in Dxtbmp, one is confronted by a bewildering array of options:
Shiver me timbers! What be all of this junk? I just want to save my file, which be the Best Mod Ever, and upload it to the waitin' crowd of scurvy dogs at HoP! Arr!!
So I did a little research, and I found a website about developing for FPS games that provides a clear & concise summary of the differences between the DXT formats.
http://reality.artificialstudios.com/twiki/bin/view/Main/TextureGuidelines
| Quote: | DDS
DDS is a native storage format, in that no conversion needs to be done when the texture is loaded, subsequently loading times are extremely fast, in the order of 5x faster than any other format. This format gives you full control over the texture attributes and color format, it also supports alpha channels. This format is therefore recommended for maximum performance and control WHEN NEEDED.
DirectX Texture Compression (Ignore unless using DDS files)
DXTC is the native, compressed texture format used in DirectX 9. In many cases, DXTC reduces texture memory usage by 50% or more over palettized, 8-bit textures, allowing for twice the textures at the same resolution, or the same number of textures at twice the resolution. Three DXTC formats are available. You can see a detailed comparison on the different types of texture compression here: http://udn.epicgames.com/pub/Content/TextureComparison/
DXT1
DXT1 is a four-bit compressed color format that allows for opaque, and one-bit alpha textures; that is, textures with no transparency at all, and textures with a single transparent color. A hardware bug in all nVidia chipsets, including the NV20 (GeForce3), potentially makes DXT1 textures gross and ugly. Specifically, decompression is performed in 16-bit color mode internally, making the resulting texture potentially unacceptable for use, especially when combined with other operations. Test your DXT1 textures on nVidia hardware before committing to their use. All other DXTC formats on nVidia hardware are okay, as textures are decompressed in 32-bit color internally.
DXT3
DXT3 adds support for a four-bit explicit alpha channel, on top of DXT1's color compression. Four-bit explicit alpha allows for sixteen distinct alpha values, making it good for textures with sharply contrasting translucent/opaque areas. DXT2 textures assume the color data is premultiplied by the alpha channel, and are not supported.
DXT5
DXT5 support a four-bit interpolated alpha channel. Three bits are used to determine explicit alpha values, and two eight-bit values are used to interpolategradually between them. This makes the format especially suited for soft gradients and other textures where the alpha areas vary less wildly. DXT4 assumes colors are premultiplied by the alpha channel, and is not supported. |
So the main difference between the DXTx formats is how they handle the alpha channel. However, note the description of a hardware bug that affects how nVidia graphics cards process DXT1 files. This page shows some good visual comparisons between several different image types:
http://udn.epicgames.com/Two/TextureComparison
Some of those comparisons make it crystal-clear why avoiding DXT1 might be a good idea. 
What are the other DDS file types, the ones that don't say DXT(whatever)? Those are uncompressed DDS files, stored at varying bit depths. Now you know....
What does this all mean? Well, for me, it serves to confirm the anecdotal experience that DXT3 seems to work best. It also explains why the DXT1 files look funky. If you're saving your mods as DXT1 files, I would recommend trying DXT3 instead.
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Steal the crew, set fire to the gold, and make the ships walk the plank!
What? Oh, NOW I get it....
Last edited by SlipperyJim on Mon Jul 30, 2007 11:41 am; edited 1 time in total |
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kernok
Swabbie
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| Posted: Tue Sep 20, 2005 3:42 pm Post subject: |
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yeah!
that's real good info for all of us begining to mod!
thank you for your lights my man 
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Cp. Kain
Gunner
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| Posted: Tue Sep 20, 2005 8:49 pm Post subject: |
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- How be me makin' me emblem be colored in defferent colors?
- Me be presumin', me gotta be makin' actual pic in different color tiles, and be usin' an inversed emblem as an alpha-channel?
- Be me right? Har har...Be never usin' DXT 1...Be thinkin' "It be the first one...be not the best..."
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Perhaps on the rare occasion pursuing the right course demands an act of Rock'n'Roll, Rock'n'Roll itself can be the right course? |
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SlipperyJim
Cutthroat
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| Posted: Wed Sep 21, 2005 7:05 pm Post subject: |
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| Cp. Kain wrote: | - How be me makin' me emblem be colored in defferent colors?
- Me be presumin', me gotta be makin' actual pic in different color tiles, and be usin' an inversed emblem as an alpha-channel? |
Hmmm ... what "emblem"? Do you mean a customized sail or flag?
Check this thread:
http://hookedonpirates.com/forums/viewtopic.php?t=569
As an aside, when I made the Noble Order of the Galleon sails, I got better results by using an inverted version of the black-and-white image as my alpha channel, then using some other color as my "main" image. I used this technique to make the sail in two different colors, red and black.
Obviously, this approach only works if the image you want to put on you sail is a single color, or grayscale at the most. A full-color image would require different handling.
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Steal the crew, set fire to the gold, and make the ships walk the plank!
What? Oh, NOW I get it.... |
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Mnemosyne
Powder Monkey
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| Posted: Fri Oct 28, 2005 4:17 am Post subject: |
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Awesome. This probably explains the problem I was having where the texture looked great before I fooled around with it, and then after re-saving it (exporting to DXT1), it got all artifact-y. I posted a thread about it, but no one seemed to have any input. Glad to see that I can go back to modding without fear of ugly textures. |
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