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 (Lists)