>The picture isn't distorted (i.e. the aspect ratio is visibly correct), so I
>assume the different x/y scaling is hard coded by the Python software to
>make up for rectangular screen pixels. Does that make sense? Is there a
Its not really anything to do with screen pixels or such. As I said in
PostScript and PDF the image is nominally set on a 1x1 unit square, and the
CTM is used to scale that 1x1 co-ordinate space to the desired actual coverage.
If we did no scaling then your image would be placed in a square 1/72 of an
inch on the side, and the resolution would be 594*72 = 42768 dpi in the x
direction and 544*72 = 39168 dpi in the y direction. It would also of
course be distorted ;-)
The scaling is there so that the image covers the expected area, and also
to make sure that it does have the correct aspect ratio. Its just the way
that PostScript and PDF draw images.