Re: Halftones in PDF files

[Michael Cudmore <mcudmore@xxxxxxxxxxx>]

Thomas Michanek wrote:
> If I have understood you correctly, you want to specify the line screen
> frequency (and possibly angle) of the halftone rasters generated in
> PostScript code for graphics or text in color or grayscale. Is that correct?

Yes.

> FM doesn't have an option to specify this, so it uses the screen settings
> specified in the printer or printer driver. If you have a PostScript
> printer driver that has a PostScript setting for halftone screens, you
> could possibly use that driver when creating the PS file. 

The postscript driver I use, AdobePS 4.5.2 for Windows 9x set up with
the Distiller 5 PPD, does not have a direct option for halftone screens,
just a resolution setting. For the physical Postscript printers I have
used with various versions of the AdobePS for Windows driver, this
resolution setting DOES seem to determine the halftone screen used, but
this doesn't seem to be the case for the Distiller printer. 

Which means two possibilities: 
1. the driver for Distiller acts differently than a physical printer,
and does not add a suitable setscreen line to the PS; or,
2. the driver for Distiller acts the same as for a physical printer, and
adds a setscreen line to the PS, but the Distiller program ignores this
setscreen when making the PDF. Although this should not be happening,
since my job options include the setting to preserve halftone screens,
and halftones in EPS artwork ARE being preserved.

However I have not taken the obvious step of inspecting the PS generated
by the driver for Distiller and comparing it with PS generated from the
same FM document by the driver for my Xerox N2125 PS. (I guess my recent
use of the Acrobat 5 PDF port, which pipes the PS straight into
Distiller rather than creating an intermediate PS file, and which mostly
works pretty seamlessly, means I am out of the habit of managing,
moving, inspecting and deleting PS files!) I will see what comes out of
a few initial tests. 

> One option could be to postprocess the PostScript file before Distilling,
> and insert a "setscreen" command at an appropriate place in the code.
> The problem is finding a place that will work for all PS files...
> 
> I have a script for inserting such a command in the PostScript code
> generated by FM 4.x and 5.x on UNIX, that will correctly set the halftone
> screen for the whole document (at least for printing; I haven't tried
> Distilling). I don't know if this would work for the PostScript created
> by FM on Windows, but it basically does the following:
> Immediately after the "%%EndSetup" line, insert the line
> "<frequency> <angle> currentscreen exch pop exch pop setscreen"
> (insert your desired frequency and angle values, in lpi and degrees)

Thank you; I will also try this method. 

Cheers,

Michael

--
Michael Cudmore

** To unsubscribe, send a message to majordomo@omsys.com **
** with "unsubscribe framers" (no quotes) in the body.   **