Questions: File Formats and Channels

[oracle]

Is any one file format better to use for alpha maps (and why)?

Is it better to separate diffuse and alpha (or normal and alpha) into two files, or use the built in alpha channel of a format that supports it?

Are there any file formats that can be easily used in Maya and Max (and edited in PS) that support more channels than rgba?

[EricChadwick]

1. DDS using DXT compression is usually the best. Because most graphics cards keep DXT compressed in their video memory, you can use bigger sizes than if you use any other bitmap format. Quality can suffer some though. But you can also used uncompressed 8bit DDS if you want, which at least lets you create the mips yourself.

Some game engines will let the artists provide source bitmaps like PSD, and will do all the DXT compression behind-the-scenes. Less control, but faster workflow.

2. Better usually to use one diffuseRGB+opacityA bitmap. Almost all bitmaps are converted into 32bit format when uploaded to the video card for rendering, so if you only use the RGB (24bit) then the game engine usually just sticks a solid-white Alpha on it, totally wasted. Sending multiple separate bitmaps can slow things down.

3. None that are supported both by game engines and by graphics cards, AFAIK. Both would have to support the format for it to be used ion a game. DirectX10 has some new formats and I haven't learned about those yet.

There are multi-channel formats for compositing purposes, like RLA and RPF, which both have the ability to include an arbitrary number of image channels. I know 3ds Max supports both, though RPF is more advanced. RLA is an old SGI format so Maya porbably supports it. Don't know about Photoshop's support though.

Great questions. I was there when I started out, had a ton of questions. Some articles here that might help you out.
http://www.rsart.co.uk/mediawiki/index.php?title=Links