Dithering problems with a barcode in a PDF document

Johan Henselmans johan at netsense.nl
Mon Dec 12 05:14:38 PST 2011


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





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