Software needed:
Photoshop 5, FoT 1.27, Red!viewer latest version
O.k. This one is for new tiles. For simply altering existing tiles, see my other tutorial.
Firstly draw a tile, or take one from a scan or photo. You will have to select it then, I suggest using the Marquee rectangular tool, selecting a small area, then from Menu Bar=>Select->Similar, and if needed Grow(remember in Photoshop you can always go back if you make a mistake). In case this is not enough(you have to be as presice as possible) additionaly use the magig wand and lasso tools(also the marquee is handy if you zoom enough to select individual pixels). Just make sure you're holding down Shift while using these presicion tools.
When you think you can't do better with selection, chose: Menu Bar->Edit->Copy, then File->New->Paste(accept the program suggestions regarding sizes). This will create a new file with a Transparent Background, and your tile picture on top. It's somewhat easier to use it now, plus you want to have a transparent background, else it will show ugly later(along with the tile). There is another way to do this, just after selecting your picture select inverse and cut, but I wanted to be sure, so I didn't do anything exactly calm minded...
Now using the already described method, reselect the image/inverse it back(Btw, it should be in RGB color so if it's not change it). Now an important part. You have to know some rough proportionate dimensions of the tile(i.e. how big it should show in game) in order for it to work. I was making a tableclock tile and these things have to be pretty small. So I checked the basic tile size(its rougly 76x40) and I made my tile at least 3 times smaller. I got lucky resing it only two times until I had the desired effect. I suggest you resort to a similar method.
Not sure about this yet, but it doesn't hurt to Ctrl-C(copy) it. From the channels screen go and press the rectangular button next to the bin that says: create new channel. A black screen with the familiar selection ants will appear. Go to Edit->Fill->Foreground color(provided it is white,else pick white manually)and 100%. Press o.k.
Now you will see that the area is white but some pixels may vary. That's fine. Leave it as is. Then go to the top Channel(RGB) and click the empty area next to it. If I'm not mistaken, the alpha should now display your tile. Save a copy as png(and preserve alpha channels), giving it a name you can identify easily, e.g. the tile's role in game. I named it clock1(as I recall at least).
*If you have little grays areas around the selection ants, go back to the picture by ticking the eye next to Alpha Channel You can select and cut the surrounding grey areas there, as Channels is just a selection tool basically. In theory you can also paint it black.Then go to the channel by re-ticking the now empty box next to Alpha Channel. The "eye" appears again. This way you can make all sorts of last minute changes, provided you keep the file open.*
Fire up the editor, tick convert directory from png to zar. You'll have to remember where you've put it. Close the editor and Start the latest RedViewer version. Open the zar you just made push the "Clip" button and add it there. Then select from the menu New->Tile, bring back the cliboard and export the zar(after selecting it-making it blue) to it.
Now all you have to do is save it under a different name somewhere you can spot it, I suggest the Test subfolder of tiles, or a new subfolder with your name. In this case you might have to put your name last in the form of F:\bos\tiles\Yourname in the relevant text file in the tiles folder. You've made your first tile and you're ready to use it!
