Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!wuarchive!decwrl!adobe!heaven!glenn
From: glenn@heaven.woodside.ca.us (Glenn Reid)
Newsgroups: comp.lang.postscript
Subject: Re: Bitmap of PostScript code..
Message-ID: <144@heaven.woodside.ca.us>
Date: 20 Feb 90 04:59:56 GMT
References: <1990Feb14.041704.14844@athena.mit.edu> <2761@bacchus.dec.com> <30006@sparkyfs.istc.sri.com> <17975@rpp386.cactus.org> <1990Feb19.172134.12850@intercon.com>
Reply-To: glenn@heaven.UUCP (Glenn Reid)
Organization: Skyline Press, Woodside CA
Lines: 65

In article <1990Feb19.172134.12850@intercon.com> amanda@mermaid.intercon.com (Amanda Walker) writes:

>That has more to do with the printer than with PostScript.  You could
>output PostScript on a plotter, or an automatic vinyl cutter, or any
>number of other devices that wouldn't know what a bitmap is if you threw
>one at them.  A PostScript program is an abstract description of how to
>render an image.  It says nothing about the actual end result
>of rendering that image.  The fact that most PostScript renderings are done
>inside 300 dpi black & white printers is irrelevant.

Not really, Amanda.  In the red book, it states explicitly that PostScript
is intended for raster devices.  Raster isn't quite the same thing as a
bitmap device, and that's an important distinction (see below)  But you
can't really do halftoning or implement even-odd fill algorithms on a
vinyl cutter.  At least I couldn't.

The real issue, I think, is that Adobe did not "prohibit" getting at the
bitmap in the political sense, they "prevented" it in the technical sense.

The point that Chris Kent was trying to make, and which Woody missed, was
that in the GENERAL sense, you cannot guarantee that the bitmap is there.
In a printer with less than a full-page frame buffer, the image might be
in a display list somewhere (there are at least 6 typesetters for which
this is true).  This is the "computer science" sense of the word "general",
not the Saturday afternoon sense of it.

Think carefully about what you might consider doing to a bitmap if you
had one, and think about these raster devices for a minute, and realize
that they are just as important as the laser printer hooked up to your
Amiga or whatever:

	* 8-bit color screens
	* 24- or 32-bit color screens (or printers)
	* color devices with CMYK, black adjustment, color correction
	* 4-bit grayscale at 92dpi (NeXT)
	* 400dpi printers
	* continuous tone color printers
	* variable-resolution devices
	* high-resolution typesetters
	* FAX machines
	* "zoom" in any display environment

I think the real point here is not that your hand will be slapped if you
steal a bitmap, but that bitmaps are really pretty big, heavy, ugly, and
useless things, for most purposes.  Scanned images are best kept as source
samples, not as halftoned bit- or byte-maps.  Everything that is reduced
to a bitmap becomes fixed, unwieldy, single-purpose, or otherwise boring.
Adobe didn't implement any but very specialized, undocumented ways of
prying the bitmap out of the printer because there are very few worthwhile
uses for it, other than feeding to another printer of exactly the same
characteristics, in which case you're better off with the PostScript
stream anyway.

Glenn

P.S.  A general admonishment:  postings that say things like "Definitely."
or "I agree 100%." or "incorrect." or whatever, should either be deleted
before sending, if you don't add anything to the conversation other than
that you agree or disagree, or else the burden is on you to say something
carefully thought-out, well expressed, and actually make a contribution.
The cost in bandwidth to the network to include a whole article and then
say "verily" at the end should be billed to the sender.  They go to China,
to Finland, to Australia, to South America, even as far as the United
States (My humble attempt to avoid nationalism)!  Every byte counts.  And
I apologize for typing so many of them.