FX 3D : PhongMaterial xxxMap's Image questions

[August Lammersdorf, InteractiveMesh]

 Following questions refer to the use of Image and WritableImage for 
 bump, diffuse, self illumination, and specular maps of PhongMaterial.

  - Can a WritableImage generally be used as a map's image?
 
  - Will the corresponding map be updated if PixelWriter.setPixels(...) 
 is called?
 
  - What are the preferred pixel formats for maps to avoid format 
 conversion and/or to achieve the fastest render speed (e.g. 
 WritableImage.getPixelWriter().getPixelFormat())?
 
  - What is the default image orientation for maps: y-down (origin at 
 the upper left) or y-up (origin at the lower left)?
 
 I'm asking because I consider supporting WritableImage for maps in the 
 3D model importers without usage of SwingFXUtils.toFXImage().

 Thanks, August