PDF output transparency problem

[eschabor]

I'm working with Scribus 1.4.1. 
My document has a PNG image that has an opaque object surrounded by transparency.  The object has smooth edges - they transition from fully opaque to fully transparent happens over a distance of a few pixels.
When I import this PNG into Scribus it looks great - nice smooth edges.
When I export from Scribus to PDF the smooth edges become jagged - the middle of the object is still opaque and the boundary is still transparent, but the transition is abrupt. 
It looks as if the full 8 bit alpha channel of the PNG image has been truncated down to just one transparency bit - 100% transparent / 100% opaque.
I've tried three different PDF viewers, including Acrobat viewer 9, and the problem shows up in all of them.
I've tried modifying various Scribus export settings, but haven't found one that solves the problem.
How can I solve this problem ?
TIA,
Stephen

[eschabor]

I've figured it out.  I was outputting PDF / X-3, and now I've learned that PDF / X-3 doesn't support transparency.
Are there plans for Scribus to support PDF / X-4 ?  Apparently it does support transparency.

[utnik]

hi stephen

scribus1.6 will allow you to export pdf/x-4 (as the developement version 1.5 does...)

utnik

[eschabor]

Nice !

I've just returned to using Scribus after an absence of a few years, and the improvements are awesome !
I find 1.4.1 to be easy to use and quite powerful - it does (almost) everything I need very well.  I look forward to 1.6