[gs-bugs] [Bug 690085] Dropouts in raster at 200 DPI

bugzilla-daemon at ghostscript.com bugzilla-daemon at ghostscript.com
Fri Sep 10 15:19:25 UTC 2010


--- Comment #6 from Ray Johnston <ray.johnston at artifex.com> 2010-09-10 15:19:22 UTC ---
Regarding the third alternative, ghostscript has a 'stochastic threshold
that usually is available to PS (using lib/stocht.ps). This creates a large 
(167x167) threshold array that reasonably emulates error diffusion without the
CPU load that error diffusion imposes.

I just wanted to mention it in case the error diffusion works. Many of our FAX
customers converting PS and PDF use this, often combined with PS code that
changes to "transfer function" to darken gray text.

Converting the ht_stocht.ps (the actual threshold array data) to a 'C' style
threshold array halftone usable by PCL would not be difficult, and I assume
that Henry could point us to the text handling in PCL to allow text to be
darkened (without affecting images or other graphics) by calling the graphics
library 'gs_settransfer' function.

On the topic of the 'downsampling' filter that prevents dropout, I have done
that for customer 531 that had similar problems with dropout (in their case
it was scanned documents in PS that needed to be rendered at 600 dpi, but
they wanted to print at 300 dpi).

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