Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Posting-Version: version B 2.10.2 9/18/84; site uw-beaver Path: utzoo!watmath!clyde!burl!ulysses!mhuxr!mhuxj!houxm!vax135!cornell! uw-beaver!laser-lovers From: laser-lovers@uw-beaver Newsgroups: fa.laser-lovers Subject: Re: PostScript printers vs. ImPress printers Message-ID: <577@uw-beaver> Date: Fri, 25-Jan-85 17:17:54 EST Article-I.D.: uw-beave.577 Posted: Fri Jan 25 17:17:54 1985 Date-Received: Sun, 27-Jan-85 07:15:11 EST Sender: daemon@uw-beaver Organization: U of Washington Computer Science Lines: 13 From: Mabry Tyson <Ty...@SRI-AI.ARPA> Thanks for the good description of the differences between PostScript and Impress. I have a question though. A significant portion of our printing is bitmap dumps of 1Kx1K screens. Since you say that the Impress description is characters, how much bigger would the description of the screen be (assuming it is fairly dense in turned on bits). The other question would be in how flexible is the description language. If I have a complicated display (not generated by some simple plotting commands), would the only reasonable way to send it to a PostScript printer be the equivalent of sending a bitmap? -------
Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Posting-Version: version B 2.10.2 9/18/84; site uw-beaver Path: utzoo!watmath!clyde!burl!ulysses!mhuxr!mhuxj!houxm!vax135!cornell! uw-beaver!laser-lovers From: laser-lovers@uw-beaver Newsgroups: fa.laser-lovers Subject: Re: PostScript printers vs. ImPress printers Message-ID: <579@uw-beaver> Date: Fri, 25-Jan-85 18:11:19 EST Article-I.D.: uw-beave.579 Posted: Fri Jan 25 18:11:19 1985 Date-Received: Sun, 27-Jan-85 07:21:25 EST Sender: daemon@uw-beaver Organization: U of Washington Computer Science Lines: 18 From: Mike Caplinger <m...@rice.ARPA> Perhaps I am confused, but Brian seems to be saying that PostScipt uses a size-independent outline description for a character in a particular font, and can arbitrarily rotate it before conversion to a bitmap. I was under the impression that there was no such size-independent representation. Isn't that what the whole hoopla over bit-tuning is all about? Certainly MetaFont is incapable of producing a uniformly great font at 300 dpi resolution, 10 point. We have used both a Xerox 2700 and an Imagen 8/300, both 300 dpi, but the character of one-pixel line drawing on the two engines is so different that CMR fonts that look great on the Imagen were awful on the 2700. Or is the outline description some incredibly sophisticated representation that takes all into account? - Mike
Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Posting-Version: version B 2.10.2 9/18/84; site uw-beaver Path: utzoo!watmath!clyde!burl!ulysses!mhuxr!mhuxb!mhuxn!mhuxm!mhuxj! houxm!vax135!cornell!uw-beaver!laser-lovers From: laser-lovers@uw-beaver Newsgroups: fa.laser-lovers Subject: Re: PostScript printers vs. ImPress printers Message-ID: <589@uw-beaver> Date: Sat, 26-Jan-85 01:51:02 EST Article-I.D.: uw-beave.589 Posted: Sat Jan 26 01:51:02 1985 Date-Received: Mon, 28-Jan-85 07:37:04 EST Sender: daemon@uw-beaver Organization: U of Washington Computer Science Lines: 41 From: Brian Reid <reid@Glacier> Perhaps I am confused, but Brian seems to be saying that PostScipt uses a size-independent outline description for a character in a particular font, and can arbitrarily rotate it before conversion to a bitmap. Nope, that is what I am saying. You are not confused. I was under the impression that there was no such size-independent representation. Isn't that what the whole hoopla over bit-tuning is all about? Certainly MetaFont is incapable of producing a uniformly great font at 300 dpi resolution, 10 point. It may or may not be impossible, but the PostScript printers do it and do it well. If you want to see an example, look at the recent POPL conference publicity. The flyer announcing the conference announcement was set with Scribe on an Apple LaserWriter in 8-point Times Roman using a font described with ordinary outlines. One of the recent issues of CACM (I think it was the November issue) had a 2-page advertisement for the POPL conference somewhere towards the back. That advertisement was also set on an Apple LaserWriter in PostScript. It isn't quite so remarkable because it uses 10-point letters and does not use any rotated fonts or graphics, but it is an example of the PostScript raster conversion. Remember that it has been through a printing press. I have carefully avoided learning anything about how the internals of the PostScript font mechanism work, because I often have difficulty keeping my mouth shut and I don't want to give away any Adobe secrets. But you may rest assured that an ENORMOUS amount of software cleverness and expertise in the nature of laser printers has gone into the PostScript system. I think that I will have to doublecheck back with the folks at Adobe to find out what I am allowed to say and what I am not allowed to say before I give you any more information about the font representation, but please understand, for the moment, that the fonts are indeed represented as size-independent outlines and that they can be artitrarily scaled and rotated before being scan-converted and that the scan-conversion works just fine in point sizes down to 4 on a 300dpi printer. Brian
Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Posting-Version: version B 2.10.2 9/18/84; site uw-beaver Path: utzoo!watmath!clyde!burl!ulysses!mhuxr!mhuxb!mhuxn!mhuxm!mhuxj! houxm!vax135!cornell!uw-beaver!laser-lovers From: laser-lovers@uw-beaver Newsgroups: fa.laser-lovers Subject: one Page Description Language dominating another Message-ID: <594@uw-beaver> Date: Sun, 27-Jan-85 17:44:48 EST Article-I.D.: uw-beave.594 Posted: Sun Jan 27 17:44:48 1985 Date-Received: Mon, 28-Jan-85 07:46:25 EST Sender: daemon@uw-beaver Organization: U of Washington Computer Science Lines: 66 From: Brian Reid <reid@Glacier> Judging from the number of questions I've received, I guess I was too obscure in my comparison of ImPress and PostScript, with respect to the statement that "neither language completely dominates the other." Both languages are complete, which is to say they can both describe any image that a given raster printer can print. At some level, both languages must fall back on the crude hack of storing rasters. There is a very wide range of page images for which ImPress must fall back and use rasters but for which PostScript can still use an analytical description. I don't need to preach to you all about the benefits of an analytical description. I am not aware of any page images for which PostScript is forced to use rasters but for which ImPress can get by with an analytical description. That is what I meant when I said it would be fairly easy to translate ImPress into PostScript. In fact, since PostScript is a programming language, all you would have to do is to define one PostSript operator that corresponded to each ImPress operator, and then turn the ImPress file from prefix form into postfix form (Impress has you say "MOVETO X Y" while PostScript has you say "X Y MOVETO")--no big deal. No further translation would be necessary. (these operator definitions would just be prepended to the front of the file). When I said that "one format does not totally dominate the other", what I meant is that the ImPress format is superior for applications in which speed is at a premium. In theory an ImPress file can always be printed faster than a PostScript description of the same image, just because the PostScript interpreter must do more computing. Our Imagen 12/240 printer, for example, can print 12 pages a minute with an 8MHz 68000 processor; the Apple LaserWriter can barely keep up with 8 pages a minute with a 10MHz 68000 processor. The principals of Imagen will remember, if they stretch their memories, that they and I spent quite some time discussing page description languages back in 1980 and 1981 at Stanford. They will also remember that at that time (long before Adobe was invented) I told them I thought ImPress was too simplistic and too limiting; they gave me various reasons why it had to be that way. Well, in once sense they have proved me wrong, because they have built a fine company with many happy customers by selling laser printers using this format that I never liked; they have good reliable products, good documentation, good customer support (at last!!), good fonts, and so forth. The Imagen 8/300 is an absolute marvel of a machine, and almost everybody that I know who has one thinks it is wonderful. I mean no harm or ill will to Imagen; I'm just glad that finally they have some serious competition, and I'm especially pleased that the competition's page description language works more or less the way that I tried to convince Les Earnest and Luis Trabb-Pardo to go with back in 1980 or 81 (whenever it was). A couple of people asked in private mail for me to compare the Apple LaserWriter with the HP LaserJet, given that they both use the same marking engine and that they look very similar. I don't think the HP LaserJet is even worth discussing as far as its page description capabilities. It's like comparing rockets and bicycles--why bother. Bicycles are cheaper than rockets; the HP LaserJet is cheaper than the Apple LaserWriter. I suppose you could throw your bicycle through the air and call it a missile; you can also engage in ultra-intense hackery and get your HP LaserJet to do something that you can call typesetting, but realistically the HP machine is just a clever variation on a daisy-wheel printer. -- Brian Reid decwrl!glacier!reid Stanford r...@SU-Glacier.ARPA
Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Posting-Version: version B 2.10.2 9/18/84; site uw-beaver Path: utzoo!watmath!clyde!cbosgd!ihnp4!houxm!vax135!cornell!uw-beaver! laser-lovers From: laser-lovers@uw-beaver Newsgroups: fa.laser-lovers Subject: Re: PostScript: comments on two issues Message-ID: <789@uw-beaver> Date: Thu, 7-Feb-85 03:20:51 EST Article-I.D.: uw-beave.789 Posted: Thu Feb 7 03:20:51 1985 Date-Received: Fri, 8-Feb-85 02:19:58 EST Sender: daemon@uw-beaver Organization: U of Washington Computer Science Lines: 84 From: Mendelson...@XEROX.ARPA The purpose of this message is to correct an error about Interpress in the recent message from Brian Reid which states: "The Xerox Interpress format is somewhat similar to Adobe PostScript, but it uses raster fonts rather than outline fonts." That is a fallacious statement. Interpress makes absolutely no assumptions about how fonts are represented. It defines a very general mechanism for obtaining character shapes that includes both raster and outline definitions. An Interpress font contains, among other things, a set of composed operators (procedures) each of which when executed causes a character of a given shape to be imaged at a previously designated position on the page. Interpress makes no statement whatsoever about the nature of the composed operators contained in a font. They can contain outline definitions of characters, or bit-map definitions, or any other representation that anyone can create. What is true is that current commercially available Interpress implementations from Xerox use bit-map representations of fonts because of advantages in performance, speed and quality. It is my understanding that current Adobe implementations require one second of time to scan convert just a single outline-defined character. By comparison, the Xerox 9700 decompresses the bit-map fonts and prints a whole page in that one second. Brian Reid also makes some statements which impute capabilities solely to PostScript, but which apply equally to Interpress. I substituted the word "Interpress" for "PostScript" and "Xerox" for "Adobe" in the following statements quoted from Reid's message, and generated equally valid statements. I quote them here with our above defined substitutions indicated in square brackets: "The important issue for contemplation on Laser-Lovers is that people understand the difference between specification and implementation. [Interpress] is not a program, not an algorithm; it is a specification language. It is completely public-domain, its documentation is available to anyone who has [$xx] to pay for the copying costs." "The important concept is that [Interpress] is a way of specifying what a page should look like, not a particular implementation of that specification, and that it does contain the expressive power to describe and use fonts in terms of outlines." "I think that the history of computer science has shown us that it is a bad idea to adopt standards that are too tightly tied to the limits of current technology. [Interpress] is a page description standard that is not limited by current raster-based technology, and for which there is a pilot implementation ([Xerox's]) that demonstrates its feasibility even with today's technology. Furthermore, it is completely public domain and it is completely independent of the word size, two's complement properties, instruction set, or addressing of any particular computer, and efficient implementations have been demonstrated on several popular modern computers." "My summary claim is that [Interpress] is the obvious choice for a standard for page specification, and that alternative implementations of [Interpress] are welcome to embody the theories of their implementors, such as the vital necessity of bit-tuned fonts or the importance of efficiency over generality. It is also perfectly reasonable to implement a[n Interpress] subset, such as all of the imaging operators but none of the scaling, rotation, or halftone and grayscale stuff, and document or market it as a subset implementation. Certainly all of the different page description schemes that are in use today can be isomorphically transformed into [Interpress] subsets. Doing that would enable a common interchange standard for images, a shared set of image management software, and would reduce the need for special-purpose "drivers" at the back end of text formatting programs." -------- I suggest an objective evaluation of Interpress and Postscript and welcome the opportunity to participate in such an eveluation. I will continue to respond to questions and comments as suitable. Jerry Mendelson