Mainly because I don't want to have to shell out the money to buy Paint Shop Pro, because I'm not going to use it for anything other than tileset making.

Does anyone know any good guides for manipulating palettes and stuff in the Gimp and Tilesetpal?

While this may not help much, Photoshop can handle palettes as well, import and export them, and easy editing.
You can do all of this via Image > Mode (Modus) > Colortable.
From there you can edit, load and save palettes (supported extensions are .pal and .act). Though the image mode has to be indexed (which should already be the case anyway).
Indexed mode means that the image has a set palette and cannot be changed without changing the palette itself (what I just explained).
Just tried to be helpful~

Thanks! I didn't know there was a free version available!

That all said, you can do everything necessary to make a tileset in GIMP, and the actual drawing process is just as easy as in any other program (in my opinion, anyway). Just observe all the usual conditions for JJ2 tilesets.

If you can't figure out how to make your image a 256 color bitmap, you need to change the image mode to indexed; in GIMP, use Colors -> Mode -> Indexed. Make your palette first, unless the tileset already has the exact colors you want in the palette, including the JJ2 sprite colors, and no others. (You will still have to rearrange them with the Rearrange Colormap option, unless you make an especially bizarre tileset where all the colors occur in the same order they are in the palette. You can do this by placing a previously made palette in the image as the first 256 pixels along the top row, if for some reason you want to.)

GIMP allows you to create and edit palettes, but it's very clunky; you can't even change multiple colors at once. While it's possible to create an entire, perfect JJ2 palette this way, you're better off using an external program like PalSuite or TilesetPal.

Do not try to use the Set Colormap option to change the palette of your tileset, because it doesn't remap the pixel's indexes - you'll get a "palette swap" effect. For a rather contrived example, if you had a palette of two colors, black and white, and another palette of two colors, white and black, using Set Colormap to switch the two would cause black to become white and white to become black.
Set Colormap is useful if you've edited an existing tileset's palette externally and want to apply it to the tileset, for fairly obvious reasons.

Another caution about palettes in GIMP: faced with two or more identical colors in the palette, it will ALWAYS use the first one if you are drawing in the tileset or adding/converting palettes with the Indexed... dialog. Yes, even if you use the Color Pick function to choose the second one, it will draw as the first one. However, changing the palette and only the palette will allow you to use the second (or third or whatever) color; change the duplicate color to a unique color in the palette, draw with that unique color, then change it back in the palette.

(And yes, duplicate colors are sometimes useful in JJ2 tilesets. Sort of.)

Even though I'm fine with Paint Shop Pro, I think this should be copied to a new thread and stickied. Good job.

Pardon me for sounding like me, but...why?

Another free program that works well is Paint.NET. It isn't as full-featured as GIMP, but the interface is a bit more standard, and it has certain tools which GIMP lacks, such as ones for drawing basic shapes (in GIMP you can do this too, but it requires more work). The main thing it lacks is the ability to edit the pallete. You can, however, save it as a 256 colour bitmap and then edit the pallete with an external tool. Overall I like it more than GIMP, at least when using Windows. It's a lot faster too.

In case someone doesnt want to buy Paint Shop Pro (didn't realize I downloaded a ware), and is forced to use Gimp. It's very helpful, and it would be nice if a tutorial like this would be easy to find.

Gimp can be used like just about any other drawing programs as long as you keep within the palette. That said, as soon as you click the index option you lose most of the filters that make it useful.

Originally Posted by Obi1mcd

That said, as soon as you click the index option you lose most of the filters that make it useful.

Well, if you're trying to draw with the palette in the first place you shouldn't be trying to use filters. Nothing stopping you from using filters in RGB mode and then switching to indexed using a premade palette, however.

Originally Posted by minmay

(And yes, duplicate colors are sometimes useful in JJ2 tilesets. Sort of.)

I have to wonder when they are ever useful. I always found them a pain to maintain, especially compared to just using slightly different colors.

Originally Posted by BlurredD

I have to wonder when they are ever useful. I always found them a pain to maintain, especially compared to just using slightly different colors.

It was useful to me when I made Diamondus V (the vector style edit of diamondus) for one of my SP episodes.

JJ2 has a funny way of doing palletes - if a colour does not appear in the tileset itself, the game will assign it to its default value. Thus, if you want to make a weird pallete edit, you need to make sure every colour appears in the tileset. Diamondus V is weird in that the majority of the pallete is the same colour (black), and the rest of it is taken by 7 colours (the tileset only has 8 colours in total, including the pallete. 9 if you count transparency). Long story short, it has A LOT of duplicates. In order to get the pallete to work, I needed to make sure that every single one of those duplicates was in the tileset itself.

This is literally the only case I can think of where there was a reason to do this, though. Normally it's not worth it.