[Therion] Maximum surface image size

[Carl Magnuson]

I created a larger background image for my growing map and now I am getting the following message:
therion: warning -- background.th [7] -- error reading bitmap -- unable to determine image size -- images/background.jpg

Is there a maximum supported size for JPG?  My new background is 15,132x11,340.  Or is it possible to input multiple surfaces for a background, so I could break that one large image into smaller tiles?

Thanks!

Carl