how can I map pixel to sceen coordinates?

[Rittscher, Jens (Research)]

Dear all,

I am writing a plug-in which allows to overlay graphics onto an image. The
position of these graphical elements are specified in pixel coordinates.

Now in order to render the overlay correctly I need to know the origin
of the image I(0, 0) in terms of screen coordinates. How can I obtain those?

Many thanks,

Jens