I've noticed that people have been using .TGA files for their CSP's, I guess this is the standard right now, and correct me if I'm wrong because I don't use CUPASH, but I guess that's the filesize CUPASH uses too.
You're all wrong, and let me tell you why.
Well I got really frustrated experimenting with different image types because PNG's are the only kind that maintain transparency, but they tend to have a large filesize, which as we all know too too well, causes the .PAC archive to get to big and crash the game.
TGA's are smaller, but don't maintain transparency, and look really ugly on the character select screen (in my humble opinion). Transparency is the reason that Nintendo used PNGs for all of their image files in the first place. Well, despair not, because I discovered a little trick that let's you save images as PNG's
AND compress them to a smaller filesize.
1. Open up your TGA's in Photoshop CS3, convert them to RGB color mode (Image/Mode/RGB), use the background eraser tool to get rid of all that Magenta ugliness, and then save the image as a PNG.
2. Go back to Image/Mode, and convert it back to Indexed color mode (Primary, Localized Color), this time as a PNG, and save it again. You'll find that the filesize is now SMALLER than it was as a TGA, and your character portraits look much better integrated with the originals!
I hope this helps some of you. Likewise, I'm sure many of you will find it useless, or already knew this. I use Photoshop, which is great, but I'm sure that there are analagous methods in similar image editing programs.