Understanding File Formats...an Impossible Dream?



Author: Jim Alley, Savannah Mac Users Group

Date: December  , 1990

Keywords: GIF TIFF PICT Paint MPNY PANT EPS EPSF

Text:
Picture file formats for the Macintosh seem to be getting more complex
every month. TIFF, PICT, EPSF, etc. I'm writing this in order to help
you understand the differences among a few of them.
A Paint (PANT or MPNT) file is produced by a program like MacPaint or
FullPaint. It is simply a collection of black dots at 72 dots per inch
(just like the Mac's screen.) No matter what printer you send a Paint
file to, it will print at 72 dpi.
TIFF files usually come from a scanner and take a long time to draw on
your screen. A TIFF file is relatively unsophisticated. It is not
object oriented. The main difference between a TIFF file and a Paint
file is that the TIFF file has lots more dpi, so it prints much better
on a LaserWriter than a Paint file. One problem with TIFF is that there
are more than 47 versions of the TIFF format, which causes a lot of
compatibility problems.
A PICT file is object oriented and is composed of QuickDraw messages
which are sent to a printer. QuickDraw is very flexible. It can go to a
PostScript printer (such as a LaserWriter, LaserWriter Plus, or
LaserWriter IINT or NTX) where it is interpreted and printed. It can
also be sent to a QuickDraw printer (such as the new LaserWriter IISC)
where it will also print beautifully. And it can also be sent to a dot
matrix printer.
Encapsulated PostScript files (EPS or EPSF) seem to be the most
confusing. First, consider the ''normal'' PostScript file. This is a
set of instructions is the PostScript language. The PostScript language
was developed by Adobe, and is the language which is built into all
Apple LaserWriters except the IISC. Normally the Mac sends files to the
LaserWriter, which translates, or interprets, the material into
PostScript commands, and then prints them. Some Mac programs, such as
Cricket Draw, work directly with PostScript. Others can save files in
the PostScript format.
PostScript files are, then, a set of commands in the PostScript
language which describes how to draw a picture. This looks pretty much
like a normal text file. It is sent to the LaserWriter where it does
not have to be interpreted.
Encapsulated PostScript files take this idea one step farther by
including (encapsulating) a PICT representation of the picture along
with the PS code. This allows you to import an EPS file into a page
layout program and see what you're getting. The PICT shows on the
screen, but the PostScript goes to the printer. This of course means
that an EPS file has two versions of the picture, one reason that EPS
files are so large.
If for some reason you import a non-encapsulated (''plain'') PostScript
file into another application, you will not see the picture on your
screen, but rather a plain gray box with a message in it saying ''This
is a PostScript drawing'' or something similar. This condition makes it
very hard to make a precise composition. 
Understanding the standard file formats is only half of the battle.
There are also all of the proprietary file formats. Take SuperPaint for
instance. A SuperPaint file saved normally goes in the SPNT format.
This picture can be easily read back into the SuperPaint program, but
no other program can understand it. However, most graphics programs
give you a choice of formats. You can ''SAVE AS*'' PICT or Paint in
SuperPaint. Cricket Draw normally saves in its own, proprietary format,
but if you ''SAVE AS*'', you can specify an EPS file. Be aware, though,
that many programs cannot read EPS back in. So you might want to save
some of your files in more than one format: (1)the proprietary format
so that the drawing can be reloaded in order to make revisions, and (2)
the EPS format for importing into page layout programs.
There are many more variants than I have been able to cover here. Yes,
I know this is complicated. I don't like it either. On the other hand,
working with the Mac gives us the ability to do so much so well with
graphics. How to cope? Experiment in order to find the method that
works best in each instance.

Copyright © december , 1990 by Jim Alley, Savannah Mac Users Group