This thread isn't meant for users who already know how to create a tileset, but for those who can't make a decent one (without offense).

Feel free to ask me anything about tileset making. If possible, also post an image of your tileset. I'll do my best to help you turn your bunch of squares into a fully functional tileset.

Ah finally, a thread for me to ask these stuff:

1. How can I convert .png or .jpg files into .j2t files?
2. What's the size of a tileset? What about the size of a tile?
3. What program do you use for making tilesets (drawing, coloring etc.)?
4. Regarding the same program, is there any way to make grids depending on the size of a tile?
5. Is there like a certain number of colors you can use for the tileset? I guess that's called a "palette".

I'm far away from being an artist but who knows, maybe I'll use this information someday.

1. If you have a .png, save it as a .bmp or .pcx another compatible format that JCS can use. I don't recommend using .jpg for tilesets, as it's a lossy format and doesn't play nice with pixel art or limited palettes.
2. A tileset will always be 320 pixels wide, or 10 tiles, as a tile is 32x32 pixels. The height needs to be a multiple of 32, and you're limited to 32,640 pixels in vanilla 1.23, and 130,880 pixels in TSF. It's unlikely you'll need a set that large, though.
3. Essentially any program that gives you control over the image's palette in some way can be used. I've seen Paint.NET suggested before, and I personally use GraphicsGale. First priority is getting the essential, tileset-specific functionality, and from there it's more a matter of personal preference.
4. GraphicsGale does indeed have a grid function, which you can specify the size of.
5. A tileset is limited to a 256-colour palette, and if you have more (and so your image isn't 8-bit) then JCS won't create your tileset file. Jazz 2 itself uses several entries from the palette (I think Disguise's Tileset Resource probably covers these?), and while you aren't forced to keep them the same as usual, it's generally better not to change them as it'll affect all the sprites on levels with your tileset.

Originally Posted by Primpy

Ah finally, a thread for me to ask these stuff:

1. How can I convert .png or .jpg files into .j2t files?
2. What's the size of a tileset? What about the size of a tile?
3. What program do you use for making tilesets (drawing, coloring etc.)?
4. Regarding the same program, is there any way to make grids depending on the size of a tile?
5. Is there like a certain number of colors you can use for the tileset? I guess that's called a "palette".

I'm far away from being an artist but who knows, maybe I'll use this information someday.

1. You don't convert a JPG into a j2t. You just don't. As for PNG, you can save it into a 256 colour BMP. The colours are guaranteed not to screw up if you save as a pallettised PNG first.
2. The width must always be 320 pixels. The height must always be divisble by 32 pixels (as each tile is 32x32 pixels).
3. I use GraphicsGale, but some use MSpain, Jasc paint shop pro, GIMP (personally I'd never use this for tilesets). Graphx2 looks like it has potential to be a good tileset making program, but also has the steepest learning curve.
4. I just use 32x32 grids. There's a program called Pyxel edit which shows tiling previews, but I've never used it myself (I'm not sure if it even supports 1x1 scaled pixels?). There's a free version of it.
5. This page here will help you a lot. Basically, you can use any colour, as long it fits the limit. Try to make textured backgrounds work in their dedicated pallette entry, which is explained on the next page.

EDIT: I was ninja'd. Argh. But theres some unique info in my post.

Thanks a lot guys, I really apreciate. One more question though, how are masks (I believe that's what they are called) done? I mean, how is a mask done and how can I add it to the tileset? Sorry if the question is not clear.

You just make a separate image with the same dimensions (width/height) and tell JCS about both of them at compiletime. Transparent is unmasked, every other color is masked. Disguise has some tips, but you already basically know what masks look like and there's only so much more to say on the subject.

Here, I have a few artistic tips for newbie tileset makers.

DISCLAIMER: This is a purely artistic tutorial. If you need any technical advice, go to Disguise's Tileset Resource instead.

CHAPTER 1: SHAPING

Lesson 1: A good alignment

A good tileset's tiles must be well aligned. This means every tile must fit with another, but there's more. When you create your tiles, don't excessively align their edges with the tile grid. We want to create a shapeful tileset, not an OCD orientated one.

As you can see, the second image looks more natural than the first.
Bad Example: MEZ01
Good Example: Medivo (JJ2)

Lesson 2: Taking shape

Be creative. Give your tiles a specific shape. If you can't imagine something, look at a picture. Go to Google Images and search for a picture, then try to replicate what you see. A shapeful tileset will be used more willingly by fellow users to create levels.

The 1st picture is nothing but a square with smoothed corners. The 2nd has a specific shape. Much better, isn't it?
Bad Example: Manufacturing Plant by me
Good Example: Space by Blade
In addition, try taking paper and pen, drawing a draft of the tiles you want to create, and then recreating them with your favorite drawing software.

Lesson 3: Going deep

Reusing the same tile and cropping the edges saves you a lot of time, but giving the edges a specific depth will make the tileset more realistic and pleasant to see.

Doesn't the 1st image look a bit too plate compared to the 2nd? Depth is important. In general, drawing something different on the edges will give a sensation of depth. You may want to include the unvariated tiles too, though, for a matter of versatility or to be used on sprite foreground layer.
Bad Example: Natures Ruins by Disguise
Good Example: Swamps by Agama

Lesson 4: Variations

Variate your tiles as much as possible, so it won't look like the world has been copypasted all around. This means you'll have to create more tiles of the same type, but with a difference in their final form. It will take time, but it's worth it.

The 1st one's tile is repeating seamlessly, but that's not what we want. We want it to look natural.
Bad Example: Evergreen Gardens by me
Good Example: Forest by Blade
Also, in the 1st tileset the soil on the sprite layer has been reused on the background layer, just with a darker color. To give your tileset more naturality, don't copy things from a layer to another. Or better, include both the copied ones and the different ones, so the player can choose which to use.
Bad Example: Castle
Good Example: Carrotus

CHAPTER 2: SHADING

Lesson 1: Border Lines

It is very important to trace the contour, possibly before coloring the tiles, because so players know exactly where are the floor, the walls and the ceiling. If you use a flawless shading, you might no longer need a contour in the end, but for now trace it.

As you can see, the 2nd image is more understandable than the 1st one.
Bad Example: River by Turtle
Good Example: Mountain by Disguise
Advanced Example: Fortress of Forgotten Sould by Blade

Lesson 2: Where's the sun?

Here things get a little harder. You'll need more than a color to make a shading. And even when you do, you'll need to make it look realistic. If the sun light comes from the upper right, use lighter colors on the upper and right sides of your tiles, and darker ones on the opposite side. You may even want to add a little light line on those to create a specularity effect. Also, don't smooth the shades more than necessary, or the shape will be compromised.

See? The 2nd image has a depth. The 1st one is a mess. Take a look at official tilesets to understand how shading works.
Bad Example: Ischa's Mine by me
Good Example: Chateau by Toxic Bunny

If anyone finds these informations useful, I'll write more.

That was very interesting.

I think a lineless tileset could look good, it's that we just don't have any good ones yet. The current lineless sets are half-assed MSpain jobs, or "lets slap on some texture and call it a day".

I think aligning the tiles to the grid is okay if it's something manmade, like metal panels or bricks.

I prefer the old medivo style over the JJ2 one. After all, castles were made of bricks. Mediv2o brings out the best of both but I still think it could feel less tiley and more organic.