On 13/3/23 03:38, Stefan Monnier wrote:
Nowadays PDF is what matters: it's the standard format for driverless
printing (along with a mix of JPEG, PWG raster, or PCLm depending on
which driverless printing standard you're talking about). Admittedly,
standards like IPP Everywhere require support only for the PWG raster
and JPEG format, while the PDF format is relegated to "should be
supported", but PDF is so pervasive and so easy&cheap to support on
current hardware that it doesn't make much sense not to support it,
except maybe for printers that focus on things like printing photos.
[ Note: this is just a guess, I have no actual data to back it up :-) ]
I have written one printer driver in the cups system for a thermal printer.
The processing chain in cups generated a raster bitmap image for me to
format and deliver to the printer. I didn't dig deep but I suspect the
previous stages involved postscript before raster conversion rather than
directly from a pdf stage.
I had a lot of problems with pdf files that did not rasterise well. Most
of that was down to the PDF files being composite nasties of bitmap
images and text (vector) elements that went through various processes
and conversions before rasterisation. They ended up smearing barcodes
into an unscannable mess.
A bitmap image or a pure vector image to start with would have been much
easier. PDF can do either but mixing vector and raster together in a
document as PDF allows is always going to cause problems for a lower
resolution printer (the standard for thermal is 203dpi). Even at higher
resolution the printed image will likely have artefacts.
I guess that was the logic behind the restriction of IPP everywhere to
PWG raster or jpeg.
Postscript does allow bitmaps in a document but a pure vector ps file
will always be easier to rasterise and will generally be of best quality
on a device. The same applies to PDF, but I suspect most PDF documents
aren't pure vector.
--
Jeremy
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