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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
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Organization: U of Washington Computer Science
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From: Mendelson.es@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