JJ1 tilesets are in the BLOCKS.### format (for example, BLOCKS.000 is the tileset for Diamondus). Each piece, or tile, is 32 pixels high and 32 pixels long. These tiles are put together to form levels. The tileset must not have more than 256 colors (each tile can have as many colors as possible, provided the colors stay constant). Animations in JJ1 tilesets, unlike animations in JJ2 tilesets, are already “animated” using in-coded pallet animation. The level designer need not worry about creating animated tiles. However, since masks differ from level to level, the level designed must create the masks for each tile.
Compiled JJ2 tilesets are in the J2T format (for example, Colon.j2t is the tileset used in the first level of Colonius). Each tile, like in the JJ1 tilesets, is 32 pixels by 32 pixels. A tile is a small image, representing some part of the game graphics. A proper tileset image always contains 10 columns of tiles, and a varying amount of rows. For this reason, tileset images are always 320 pixels in width. The height may vary, but is always a multiple of 32 pixels.
In the original JJ2, a tileset may not exceed 1024 tiles in size, but since version 1.24 (used for the The Secret Files and Christmas Chronicles add-ons), a tileset may strech on to 4096 tiles in size. However, animated tiles, or tiles put together in JCS to create an animation, also count. You must be one tile under the limit (the tile can be used but then causes errors).. Therefore, a tileset that is 1000 tiles big can only have up to 23 animated tiles in versions before version 1.24. Unlike JJ1 tilesets, however, the masks come with the tileset.
Tilesets are created out of two 256-colour image files (allowed types are BMP, PCX, ANM and LBM) with JCS. One image contains the general look of the tileset, and the other contains the tileset mask. If the the Auto Mask option is used during creation of the J2T file, the game attempts to create a mask out of the image with the tileset, and a separate mask image is not required. This can result in flawed masking in the resulting tileset. The two transparent colors for a tileset are 0,0,0 (black) and 87,0,203 (a light-purple blue).
Making a JJ2 tileset is easy; simply make your tileset (make sure that the tileset picture is 320 pixels, or 10 tiles wide, and that the picture length is a multiple of 32), make a mask file to go along with the tileset, and compile them in JCS.
Eat your lima beans, Johnny.