PS3 Wallpaper size

When I want to put a wallpaper of my own on the PS3, the whole image doesn't fit. You have to move around the box thing to select part of the image. My question is this: what is the size of the " box " in pixels. I've tried 1440by900 but thats too big. Does anybody know?

the resolution is 1920x1080 or 1280x720 o and you should try to zoom out with the right analog stick moving down