Any requirements for images drawn on screen?

I have not had luck finding this and was wondering if there was some documentation somewhere describing what can and cant be rendered to screen. The reason I ask is I am displaying data in a tabular fashion using roCanvas. I wanted a graphical background to display behind the text I am printing to screen but when I use the png image I created in photoshop with a size of 1280x720 and a transparency layer, I get nothing. However if I use a smaller graphic, that does not have transparency, the image shows up. I am assumign this is a restriction onthe device and was hoping I could better find what is allowed. Any help would be great. Thanks!

pics = []
pics.Push({
url: "pkg:/artwork/travel.png"
targetRect: m.canvas.GetCanvasRect()
})
m.canvas.ClearLayer(3)
m.canvas.SetLayer(2,pics)
m.canvas.SetLayer(3, m.decodedText["sid"])