[gs-bugs] [Bug 691923] Differences in dithered output with ps2write

bugzilla-daemon at ghostscript.com bugzilla-daemon at ghostscript.com
Mon Feb 7 17:10:41 UTC 2011


--- Comment #3 from Ray Johnston <ray.johnston at artifex.com> 2011-02-07 17:10:19 UTC ---
Just a stray comment about halftones (I'm sure Ken knows this, just putting it
here for others that may consult the bugs for help)...

In the real world of PostScript, many PS files set halftone
in ways that may be undesirable for a printer. That's why most PS printers
that want to preserve image quality (true of most color laser printers) will
    << HalftoneMode 1 >>  setuserparams

This allows the printer manufacturer to 'lock in' the halftone so they won't
get unpredictable colors due to a particular file's screening (which can
drastically affect the color correction). A file that wants to 'take over',
can still set the HalftoneMode to 0 before setting their screen (presumably
also their CRD), but this is not done by most printer drivers or applications
that spew PostScript.

Unfortunately, this is a LL3 userparam, so while Ghostscript can handle it
without a problem, a PS Level 2 interpreter/printer won't take it.

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