Path: utzoo!utgpu!news-server.csri.toronto.edu!rutgers!mcnc!rti!dg-rtp!bigben!bigben!philip From: philip@beeblebrox.dle.dg.com (Philip Gladstone) Newsgroups: comp.lang.postscript Subject: Re: Halftoning Algorithm Message-ID: Date: 23 Nov 90 15:07:12 GMT References: <7344@hub.ucsb.edu> <3273@medusa.informatik.uni-erlangen.de> Sender: usenet@dle.dg.com (Net News) Organization: Data General, Development Lab Europe Lines: 29 In-Reply-To: eckert@medusa.informatik.uni-erlangen.de's message of 22 Nov 90 19:47:04 GMT In article <3273@medusa.informatik.uni-erlangen.de> eckert@medusa.informatik.uni-erlangen.de (Toerless Eckert) writes: eckert> - Conclusion: if you need to render images on low resolution (300dpi) eckert> printers with more spatial resolution than the standard dot function eckert> of postscript, use ordered dither. It can be done simply by eckert> redefining the spot function and the transfer function. After some private discussions with other netlanders about this, I don't think that you can redefine the spot and transfer functions to achieve this. It turns out that in *at least* one implementation of postscript, the spot function is called during the execution of the setscreen operator (AND NOT during the display of grey levels), and the transfer function is called during the execution of the setgrey operator. I admit that I have not tested when the transfer function is called for images -- but I would expect it to be called once for each SOURCE point. All this is consistent with reducing the amount of work that the interpreter has to do (i.e. goes faster). Of course, all this may be wrong, and I'd be only too pleased to be contradicted by a piece of postscript posted to the net! -- Philip Gladstone Development Lab Europe Data General, Cambridge England. +44 223-67600