[NTG-context] When newsizing an external figure bei [width=<some pt>], what will be its height in pt and viceversa?

Hi All, from an external figure I normally know its width and height in px. But I don't know its exact sizes in pt. When newsizing the figure in a document (by the same width-to-height-ratio), I'll do that as some part of textwidth or textheight, in pt or mm, but not in px, i.e. by means of [width=<some pt>]. Sometimes it would be interesting to know its new height in pt, and viceversa. Is there a variable or something else containing its new size in pt? Regards, Rudolf