looking for COLOR HALF-TONE SCREEN algorithm(s) and advice

looking for COLOR HALF-TONE SCREEN algorithm(s) and advice

Post by Pete Holzma » Wed, 02 May 1990 11:55:00

I'm looking for references (to code and/or algorithms) for producing bit-map
color output using a half-tone screen algorithm. Since printers use half tone
screens to get lots of colors out of 4-color presses, it seems the same
technique would work well when trying to get 4-color (3 + black) computer
printers to do the same thing.

Algorithms for both variable width line and filled-area output would be useful.
I'd like to play with changing the angle of the screens (rotating them
separately in the X-Y and/or Z planes). Presumably, the screen is a true
filter, so that the final output is clipped at full resolution to the original
dimensions of the object being output.

I can (and probably will end up doing...) spend a lot of time to figure out
how to do all this, but if anybody has already done it, it would sure save a
lot of time! Are there any references to algorithms like this? Can anybody
think of anything else to add to it?
  OOO   __| ___      Peter Holzmann, Octopus Enterprises
 OOOOOOO___/ _______ USPS: 19611 La Mar Court, Cupertino, CA 95014
  OOOOO \___/        UUCP: {hplabs!hpdsd,pyramid}!octopus!pete
___| \_____          Phone: 408/996-7746


1. Need Half-Toning Algorithm suited for HP-Laserjet

        We are in the process of trying to print a grey-scaled image on
an HP-laserjet, which has an output characteristic of 300 dpi, monochrome.
The image file contains 8 bit/pixel grey scale values.  Although we can
get a printable image using NeWS to do the half-toning, it appears that
a half-toning algorithm used for a CRT display device isn't really cut out
for producing an image tailored for a 300 dpi output device.  Anyone out
there know of a public domain filter that may do this?  A posting or direct
email response would be much appreciated.

        (I did see the recent posting by Ed Falk, containing the two
dithering filters "odither.c" and "fsdither.c".  However, the real question
is, has anyone studied the characteristics of the HP-laserjet and tweeked
a half-toning algorithm accordingly?)

        Thanks (wishful thinking)

        Paul Matz
        PPG Biomedical Systems
        One Campus Drive
        Pleasantville, NY. 10570

PS: Sorry if this gets posted twice.  Something is not quite right with
    my postnews.

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