Text Object height

Hi,

I'm using Report Lab to generate a document and directly drawing objects on
the Canvas in the header section.  I'm drawing an image in the top left and
text object to the right of it.

To calculate the text object height I'm calling getY after begin text and
again after the last text line is drawn.  Deducting the first from the
second gives the height of the text object.

Even though the text object is taller than the text object the actual
height of the image in pixels is bigger than the height of the text object;
which doesn't make sense to me.

Am I missing something?  How can I get a comparable height?  I need this to
work out the available height for the flowable render section (main
content).

Steve