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