Dithering problems with a barcode in a PDF document

[Helge Blischke]

Johan Henselmans wrote:

> Some years ago, I have developed a printer driver for a 200/300/600 dpi
> boca printer that translates the black/white cupsraster images in the
> raster of the printer.
> 
> The printer supports downloadable fonts and has internal barcode fonts,
> and a possibility to download images etc.
> 
> So the filter is defined as
> 
> Filter application/vnd.cups-raster 100 rastertoboca.
> 
> That works well with standard data, like text and images (allthough this
> could have some improvement...) but it is not working well with
> barcodes: If the barcodes are small in the pdf document, then the
> rastering is really horrible and makes the result unusable for scanning.
> the bars look ragged, and sometime the empty space between bars is
> completely filled up.
> 
> The path that was used for the output was: pstoappeps| pstocupsraster|
> rastertoboca.
> 
> I did some measurements of the PDF: the narrowest bar in the barcode is
> about 0.29 mm (0.029 cm), which is about 2.3  pixels at 200 dpi and 3.42
> pixels at 300 dpi.I can imagine that this might result in pixel sometime
> to become black, and sometime to become white, if barcode is not layed
> out exactly on the margin of a pixel.
> 
> Is there any way I can make this barcode look like it should be, by
> adjusting the dithering?
> 
> Should I consider to parse the pdf file into text and image objects and
> feed these to the printer?
> 
> Kind Regards,
> 
> Johan Henselmans

My suggestion is to replace the pstocupsraster filter by the latest 
gstoraster filter (see the links on the CUPS web site for details) and then 
add 
-c true setstrokeadjust
to the array of Ghostscript options (see the documentation and look into the 
Perl script.

Helge