Blender-pack image file format?

melviso

Out of curiousity, if you create a new image file in Blender for texture painting and you pack the image file with Blender. What file format does Blender pack it as? I noticed the pack as png in the uv editor but for a new image file created inside blender, does Blender pack it with a custom file format?
I now work with Tiff file 16 bit format uncompressed, so how can I get Blender to pack the new image created inside Blender with this format?

MmAaXx

I guess it is a compressed openEXR. 

melviso

Ok, thanks.