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Hello, I have problem with print quality.In sumatra is printed text made by many little dots instead of continuous black surface.The PDF file is very clear, but the printed sample has quality defects. May I ask what caused it?

The printers currently in use are ZDesigner GK888t, DASCOM TL-200, DASCOM DL-210Z, these three will have quality defects. Path of my PDF source file:tmppdfFile/test.pdf at main · callmePicacho/tmppdfFile · GitHub,

Application: wkhtmltopdf 0.12.6
Page Size: 5.4 x 3.21 cm

Printed picture:

. Is this a print command problem or another problem, print command:

SumatraPDF -print-to-default test.pdf

A PDF file is designed to hold printer contents but is not the best format for printing small thermal labels unless you consider each factor.

Zebra printers use a text language (ZPL) so either the PDF or PNG need to be converted into a black and white (B&W) set of lossless aliased instructions.

However Windows default is coloured, lossy, anti-aliased imagery, thus there is likely to be two problems.

  • The edges of blocks that are not registered exactly on a B&W pixel boundary will be anti-aliased to form a staggered edge when aliased.(You can see that in both the chrome and SumatraPDF outputs, but its more noticeable via SumatraPDF reliance on windows driver resolving the median values)
  • Conversion from lossy to lossless produces unwanted artefacts such as halos and speckling.

The way to avoid windows degrading a source PNG is to pass that through a Driver that holds the edges as aliased (or anti-aliased GREYSCALE) and does not use coloured jpeg or other PHOTO-graphic approximations to replace the crisp Graphics.

To get perfect thermal printing results the application needs to be designed to handle thermal printing and work with a thermal print driver. For that Zebra Designer is the perfect choice.

Having said that many SumatraPDF users get a passable output (QRcode can be degraded by 30% and still work) on a range of thermal printers by using Bartender or similar drivers that try to correct the colour to mono aberrations.