Why the ugly PNG pictures?

[Aleksandar Kanchev]

Hello list,

whats wrong with LyX and PNG files? I draw a diagram in MS Visio, export 
it to PNG, open it on LyX 1.5.5 (on Fedora 9). The PNG looks  nice in 
LyX itself, but when I create a pdf the picture gets over-scaled beyond 
the page size. I tried forcing the picture size in lyx but it looked 
like it was first over-scaled, then scaled again to the size I gave it 
and as a result it looked completely ugly. This seems to be a problem 
with PNG files, I tried exporting from MS Visio the same file with the 
same size in JPEG and it displayed ok in LyX and the picture wasn't 
over-scaled I left it to automatically scale the picture.

Am I doing something wrong? Is there a known problem with PNG files? 
Could it be fixed? I really don't like JPEG, the diagram looks better in 
PNG. The picture size is 14x11,2 cm or 529x423 pixels.

best regards,
Aleksandar