DDS Compression issue

kodde

Hey guys.

Another issue for you today.
I'm playing around in MentalMill making CGFX-shaders. Anyway, I'm trying to save a specular map texture from Photoshop with the DDS-plugin. I'm setting it to DXT1 preset and it produces green/purple artifacts even though I only have black/white tones.

There's another issue as well. Which DDS-preset do I use to save a 1 channel compressed specularmap? Using RGB channels to produce a grayscale image seems wasteful.

Thanks!

Eric Chadwick

DXT1 is particularly bad at saving grayscale, since the green channel is stored in a slightly higher color depth than the other two channels. So you'll get green & purple artifacts here and there.

If you don't mind the filesize, L8 is a pretty good choice for single-channel grayscale. You could also try packing four grayscale maps together in a single bitmap and use DXT5 format.

kodde

So I cannot use the same compression as DXT1 och DXT5 but only with one channel? I've tried the L8 as you mentioned, I was mostly just curious if there was a more optimal way.

Thanks

MoP

Why not just have coloured specular? It looks way better...

Neox

or are you using the alpha of your diffuse for anything specific?

kodde

I don't actually have any real scenario to use this yet. Setting it up for test purposes when working with MentalMill.

MoP> I'm asking purely out of curiosity. Not used to working that much with DDS-textures yet.

Neox> Yeah I see what you are hinting at, finding a spare channeling in a texture map I'm already using. Let's say I'm using the alpha of the diffuse for transparency, and I won't be needing a colored specular. How would you tackle that scenario?

Thanks

Eric Chadwick

Use the alpha of another map.

You could use RGB for the colored spec, and the alpha for spec power (width).

Actually, DXT5_nm is a format where you only use the Green and Alpha channels, leaving the other two blank. Something like that might float your boat.

kodde

Cool.

Thanks for the info. I will try this later when I'm at work.