PTG
From Just Solve the File Format Problem
PTG (Painting) is the proprietary format used as the native image format of ArtRage, a paint program which apparently supports wet paint, since the official site claims that the information stored in the file includes "how much paint there is on the Canvas and how wet it is." ArtRage supports some other, more commmon, file types, to which you can save an image using the "Export" feature.
Identification
Files begin with the ASCII string Ambient Design Project file, or hex 41 6D 62 69 65 6E 74 20 44 65 73 69 67 6E 20 50 72 6F 6A 65 63 74 20 66 69 6C 65.
