There's no need to convert a PNG to JPG at all. PNG's compression
algorithm is supported via the Flate filter. The only problem with it is
that it's just the IDAT section of the PNG file. But the rest can be
embedded too:
https://stackoverflow.com/questions/14220221/how-to-insert-transparent-png-in-pdf#answer-20001230
Btw transparency is not allowed in PDF/A-1.
Levente
On Mon, 12 Jan 2015, Stephan Eggermont wrote:
Olivier wrote:
In fact, the PNG is converted to JPEG image before to be included in the PDF
file.
But the conversion process doesn't support transparency and sets a black
background.
Jpeg doesn't have transparency. For browsers there is a hack.
http://jim.studt.net/jpeg-alpha/
http://stackoverflow.com/questions/14220221/how-to-insert-transparent-png-in-pdf?rq=1
PDF supports transparency since PDF 1.4
To avoid trouble, only use images with the same color space and either a
1 bit mask or a clipping path. Composing images in different color spaces
with an alpha channel seems to be difficult to get right.
Stephan
