Path: utzoo!utgpu!news-server.csri.toronto.edu!rutgers!usc!sdd.hp.com!decwrl!adobe!heaven!glenn
From: glenn@heaven.woodside.ca.us (Glenn Reid)
Newsgroups: comp.lang.postscript
Subject: Re: open pre-press interface OPI 1.1
Keywords: postscript tiff image pre-press pagemaker
Message-ID: <207@heaven.woodside.ca.us>
Date: 14 Jul 90 02:56:13 GMT
References: <1289@media01.UUCP>
Reply-To: glenn@heaven.UUCP (Glenn Reid)
Organization: Skyline Press, Woodside CA
Lines: 67

In article <1289@media01.UUCP> pkr@media01.UUCP (Peter Kriens) writes:
>--------
>[ OPI is a defintion from ALDUS [Pagemaker] that allows
>[ the manipulation of high res pictures in postscript while
>[ the end user uses a low res version. The spec can be
>[ obtained from Aldus: Developers Desk, Aldus Corporation, 
>[ 411 First Avenue South, Seattle, Washington 98104 (206)-628-6593

>While writing software for using the Aldus
>OPI defintion for high def pictures in postscript,
>we have found something peculiar. Is there anybody
>who can verify those facts for us?

>In OPI you specify the original size of the picture
>in pixels. Now it seems to me that pixels are a nasty
>way of measuring sizes. If I make a low res version
>from my picture and give it to the end user, he will
>use quite a different resolution than what I store
>on the main system. I do not want to include the low
>res in a high res tiff file because then I would still
>need to send all the data to the user.

I had a look at the specification for "OPI" a while ago,
when Aldus was just bringing it out.  The problem you
point out is very real, and to my mind, makes the format
more or less useless.  As I recall, you can't scale it,
and it won't work at a target resolution that's different
from the one you originally specified.  In short, it's
an expedient hack, not really a solution to the problem.

The problem, however, is quite real.  With high-resolution
sampled images (especially in color), there are a whale
of a lot of bits, and it's no fun even to store them on
the disk, let alone ship them around over the network.

OPI is intended for real Pre-Press systems, so you can
scan a photograph on a Scitex machine and leave it on
the Scitex.  You can then design your page with a low-
resolution version of the file on your personal computer,
and when you're ready to really print, you can figure
out what transformations and cropping to apply to the
original file that should be still on the Scitex disk,
unless somebody deleted it because they needed the space.

Part of the issue is whether or not you really have a
PostScript interpreter in the final pass (e.g. on the
Scitex machine).  The PostScript code that does not
represent the image itself must get interpreted and
rasterized eventually, and merged back together with
the image.  I remember saying to the engineer at the
time (and having him agree with me), "...so if you
have a PostScript interpreter at the end, this convention
doesn't help you, and if you don't have an interpreter,
it doesn't work [when you scale something]."

My recollection of OPI is admittedly a little fuzzy and
it may have been fixed since I last saw it, but the fact
that you raise the same issue leads me to believe that
it's essentially still device-dependent and really only
a partial solution....

/Glenn

-- 
 Glenn Reid				PostScript/NeXT consultant
 glenn@heaven.woodside.ca.us		Independent Software Developer
 ..{adobe,next}!heaven!glenn		415-851-1785