Path: utzoo!attcan!uunet!decwrl!adobe!heaven!glenn
From: glenn@heaven.woodside.ca.us (Glenn Reid)
Newsgroups: comp.lang.postscript
Subject: Re: Definition of EPS vs PS
Message-ID: <203@heaven.woodside.ca.us>
Date: 10 Jul 90 01:55:02 GMT
References: <3911@crystal9.UUCP>
Reply-To: glenn@heaven.UUCP (Glenn Reid)
Distribution: comp
Organization: Skyline Press, Woodside CA
Lines: 60

In article <3911@crystal9.UUCP> derosa@motcid.UUCP (John DeRosa) writes:
>I am having an arguement with a fellow worker about
>the difference between encapsulate postscript and 
>postscript.
>
>He says that an EPS file is: "An Encapsulated Postscript 
>file is merely a postscript file with two additional
>lines added at the begining:
>
>	%!PS-Adobe-2.0 EPSF-1.2
>	%%BoundingBox: 0 0 612 792"
>
>I really don't know what it is.  

I wrote the original (now antiquated) specification for Encapsulated
PostScript files, so I'll hazard a guess.  The remarks your friend
made, I would say, are "necessary but not sufficient".  Well, really,
that is being too kind.  They are a hack that *might* turn a file into
an EPS file, if it just happened to already be one.  But in general,
just adding those comments won't do it.  That is a little bit like
making an Objective C program into a vanilla C program by changing the
extension from ".m" to ".c"

If you want a brief description that isn't quite the whole truth, an
Encapsulated PostScript file is a well-behaved PostScript file that
can be safely imbedded into another PostScript program as an
illustration.

This makes EPSF effectively a subset of the PostScript language.  For
instance, you cannot use the operator "erasepage" in an EPS file,
because it would erase the entire page, including the rest of the page
on which it was supposed to be an illustration.  It also must only be
a single page in length (imagine using a 52-page document as an
illustration on page 3 of your newsletter).

For a more complete definition, get a hold of the specification for EPS
files from Adobe.  I imagine you will get several follow-ups to your
posting, one of which is sure to have the details on how to get the spec.

Adding %! to the beginning of the PS file doesn't change anything about
it.  There are, however, many applications that support EPS files, and they
won't even consider importing the file without the necessary header
comments.

NOTE: It is generally a bad idea to add comments to a file by hand.
Those comments are a "guarantee" that the file adheres to the EPSF
specification, and if the file doesn't adhere to it, you wouldn't want
to make it tell untruths to the importing application.  Sometimes you'll
get lucky, often you won't.

I hope this helps a little bit, although it doesn't seem all that clear
when I glance back through it.  Getting a hold of the spec from Adobe
will make it the most clear.

/Glenn

-- 
 Glenn Reid				PostScript/NeXT consultant
 glenn@heaven.woodside.ca.us		Independent Software Developer
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