Stefan Roellin wrote:
I have submitted a patch which (slightly) improves the quality of the print
plugin (see Bug #387604). The problem basically was that Postscript can't
cope with transparency. In contrast, PDF is able to do so.
The current implementation/patch now has a disadvantage: if you print to a
postscript target, the image has to be exported TWICE: once for the 'print
preview widget' (with alpha) and once for the postscript target (without
alpha). This is certainly not optimal regarding memory consumption.
So the question is, whether this is a real problem or not.
For me, it is a serious problem. I work in the print industry, typically
creating PostScript drivers. The PS output is quite good quality, and
every conversion generally suffers serious quality issues. Gimp is one
of the best tools available for UNIX side PostScript. Photoshop and some
other tools, despite being Adobe products, tend to break standards
compliant high end print systems (most of those products work great so
long as you don't mix them with other people's products, then they
suck...gimp PS works flawlessly with all of the certified systems). As
soon as you start making PDF-to-PostScript conversions or
PostScript-to-PDF-to-PostScript, the output is hopeless. Don't do it.
If yes, a solution could be to not distinguish between a Postscript and a
PDF target (i.e. to embed only opaque images into a PDF despite the fact
that PDF can handle images with alpha values). In this case, we only have to
export the image at most once.
PDF is pretty much a subset of PostScript with a hierarchy, at least in
the basic early versions. When you start getting into more recent
versions, it diverges, but still contains mainly a subset of PostScript
operators for the vector and bitmap part of it. If you wanted support
for PDF, you'd be better off making both PS and PDF output options. It'd
be nice to have direct PDF output, but this is a document interchange
format, and NOT a print format. There is no reason to not add dual
output format, but there is an extrordinary loss of quality by removing
direct PostScript output (FYI, I must often slice and dice the raw
PostScript, and gimp has the most sane version among the common tools).
FYI, a proper conversion tool can convert from PS to PDF without loss,
but virtually all tools have issues, mainly when converting vector to
bitmap, or using lossy compression without an option to say no to it. If
anyone really felt the need to improve print options, my own feeling
from coding for the print industry is that more options on compression
formats and font embedding (perhaps not relevant for gimp) would be
D. Stimits, stimits AT comcast DOT net
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