Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Path: utzoo!mnetor!uunet!seismo!gatech!bloom-beacon!husc6!cca!mirror!xanth!kent From: kent@xanth.UUCP (Kent Paul Dolan) Newsgroups: comp.graphics Subject: Re: Thining out a bitmap image. Message-ID: <1649@xanth.UUCP> Date: Thu, 23-Jul-87 00:57:38 EDT Article-I.D.: xanth.1649 Posted: Thu Jul 23 00:57:38 1987 Date-Received: Sat, 25-Jul-87 06:40:00 EDT References: <275@uvicctr.UUCP> Reply-To: kent@xanth.UUCP (Kent Paul Dolan) Organization: Old Dominion University, Norfolk Va. Lines: 35 Keywords: don't bother to look at the surrounding input Summary: sounds like a halftone screen John, Having read your original and followup posting, and several replies, I thought I'd stick my oar in, too. ;-) Back when I used to be involved with the creation of nautical charts, we worked with an 800 dots per inch laser onto film plotter, and had a similar problem, turning black areas into grey areas. Our solution depended on the original data being "blobby", rather than "speckled"; i.e., the original had no isolated dots. We used a physical solution, a half tone screen, just because it was _much_ cheaper than trying to process our data after the potential for run length coding was destroyed (our graphics format was 1.6 billion pixels, 7 bits deep, so we had a bit of a storage nightmare without run length encoding). Anyway, for your purposes, and if it is appropriate, just develop a mask pattern that achieves the separation you want, and then go through and turn all the masked out pixels to white, whatever their original color was, and only allow the data through where the mask allows. This saves lots of computation, since you don't really have to consider more than one pixel at a time. If you get in the color business later on, there is an analogous use of half tone screens for color. As I remember, the trick is to rotate the mask a number of degrees that avoids moire fringes. Consult your local tech library's color press printing literature for more detail than I am competent to give. Kent, the man from xanth.