• ARKPntEditor
  
• Graphic editor – I use GIMP but feel free to use anything that works for you

There are three types of sail template file names that ATLAS will recognize:
SailGeneric_C – raft sail and small sails of any type
SailDouble_C – medium sails of any type
SailTriple_C – large sails of any type

Game won’t recognize if template is Speed Sail, Weight Sail or Handling Sail so be aware which template you using on which sail type.

Download and unzip this sail template archive[goo.gl].

I recommend you use of this ARK guide for ATLAS painting. There is already updated version of Ark Paint Converter[drive.google.com] that works with ATLAS .pnt files

If for some reason you want to use ARKPntEditor keep reading :)

Download ARKPntEditor[www.voicemacro.net] if you don't have it


Download graphic editor if you don't have one


Run ARKPntEditor open any of .pnt from unzipped archive. You should see this:

Select "Save as image" to create .png file.
Open this png file in your graphic editor and add transparent layer. Also open image(s) that you want to place on your sail and prepare it accordingly to opened template (resize, crop, etc..) - if you don’t know how to handle this part google/yt for basic graphic editing tutorial. (it is really easy but making screenshots of all this basic steps is pointless when thousands of other people's already done it or even recorded movie guides about it).
Place prepared image on transparent layer that you created before and fix any details that need to be fixed.
Hide original image or delete it - leave only layer with your image. Save .png in graphic editor and select "Load image" in ARKPntEditor and confirm color correction. You may want to use "Show costs…" and "Limit colors…" functions for final fix.
*BUG WARNING: There is a bug with Forest coloring in ATLAS so make sure that you remove this color of your .pnt file*
Select "Save as ARKpnt file" and use desired name with correct suffix _SailGeneric_C.pnt / _SailDouble_C.pnt / _SailTriple_C.pnt

In this case I opened HandlingLarge_SailTriple_C.pnt and saved it as Done1HandlingLarge_SailTriple_C.pnt

Copy your .pnt files into [...]\YOURATLASDIRECOTRY\ShooterGame\Saved\MyPaintings
When you hit sail with paintbrush in game and select "load painting" you should now see avaliable templates.

(The latest version of this steam guide can always be found here)

Good luck, have fun and I'd like to wish you happy painting ;-)