PTG

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, or hex.

Links

 * Wikipedia article
 * Working with ArtRage files
 * Discussion of file conversion
 * FILExt page