Hello to everyone... and welcome to my first mini-tutorial and it's all about getting that nice mangled edge to "treasure maps". Coyotemax did one for the September Big Challenge... and I had no clue how to do a nice one but I think I've found a nice shiney way that is all thanks to RobA Captain of the River Police...
So, credit where credit is due: RobA's Realistic Map Creation Tutorial is the basis for this little trick.
This should work in PhotoShop, but I don't know the names of the commands for Photoshop, just the GIMP terms.
STEP 1: Make your map.
Use whatever methods you usually do to make your nice olde-style map on parchment. The point is to have a finalised map to work with.
STEP 2: Add in a layer on NORMAL mode (say called MASK)
Fill the whole thing with WHITE. Plain-ol' 256-256-256 white.
STEP 3: Gaussian blur
Blur the edges, the heavier the blur the more damage your map will take. For a map at 1024x768 I'd personally suggest a 50px - 75px blur.
STEP 4: Add ANOTHER layer on OVERLAY mode (Say called CLOUD)
Fill this with a randomised solid noise cloud. Put the detail to 15, X to 16, Y to 16, click the "randomized" tick-box and create your cloud. Make sure this layer is ABOVE the layer called MASK
STEP 5: Fidget with the Levels of your Cloud
Use the LEVELS dialogue to manipulate the CLOUD layer to adjust the scraggly edges of the MASK layer.
STEP 6: Selecting the undamaged part
Take the Select-by-Colour (finger pointing at the RGB) Tool. Check the SAMPLE MERGED tick-box. Select all of the MASK layer, then using the Select-by-Colour in "Subtract Mode", click near the edges of the blurry scraggly white, click around the edges until you like the rough shape. Fine tune the scraggly shape with the Lasso (to remove any "islands").
STEP 7: Selection to Mask
Selection > Save to Channel
STEP 8: Add Layer Mask
Add a layer mask to your MAP layer. From the options in the list choose "Channel" at the bottom of the list and click Add.
You now have an edge-damaged map suitable for any childhood dress-up day at school to do with Pirates and there were no candles involved...
For an example check out the entry I made to the October Big Challenge...