Understanding File Formats
ÉAn Impossible Dream?

Even though Macintosh graphic formats can seem to be a bewildering topic, picture file formats fall into four universal formats: MacPaint, TIFF, PICT, and EPSF. Knowing how these four formats relate to each other can help you to manage your documents.
A Paint (PANT or MPNT) file is produced by a program like MacPaint or DeskPaint. It is simply a collection of black dots at 72 dots per inch (just like the MacÕs screen), and it is always 8" x 10". No matter what printer you send a Paint file to, it will print at 72 dpi. 

A Paint file is often called a bitmap, although technically TIFF files are also bitmaps. (Adobe PhotoshopÕs use of that term is incorrect and confusing; what they really mean is line artÑa bitmap which has only pure black and pure white pixels.) 

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 can have lots more dots per inch, so it prints much better on a LaserWriter than a Paint file. Also, each dot (or pixel) can be a different gray or color with the TIFF format. One problem with TIFF is that there are more than 300 versions of the TIFF format, which causes a lot of compatibility problems.

A PICT file is object-oriented (although it may also contain a bitmap) and is composed of QuickDraw messages which are sent to a printer. QuickDraw is very flexible. It can go to a PostScript printer where it is interpreted and printed. It can also be sent to a QuickDraw printer (i.e. a non-PostScript printer) where it will print beautifully. And it can be sent to a dot matrix printer.

One of the primary benefits of an object-oriented PICT file is that it can be resized without the distortion that comes from stretching a bitmap.  The main disadvantage of the PICT format is that many page layout programs do not work very well with it.

Encapsulated PostScript files (EPS or EPSF) seem to be the most confusing. First, consider the ÒnormalÓ PostScript file. This is a set of instructions in the PostScript language. The PostScript language was developed by Adobe, and is the language which is built into manyÑbut not allÑlaser printers. Normally the Mac sends files to the laser printer, which translates, or interprets, the material into PostScript commands, and then prints them. Some Mac programs, such as Aldus FreeHand and Adobe Illustrator, work directly with PostScript. Other programs (such as MacDraw Pro or Canvas 3) can save files in the PostScript format.

A PostScript file is, 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 laser printer, where it does not have to be interpreted.

Encapsulated PostScript files (EPS or EPSF) take this idea one step farther by including (encapsulating) a low-resolution PICT representation of the picture along with the PostScript code. This combination allows you to import an EPS file into a page layout program and see what youÕre 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. EPS files, like object-oriented PICT files, can be resized without distortion.

If for some reason you import a non-encapsulated (ÒplainÓ) PostScript file into another application, you will not see the picture on your screen, but rather a plain gray box with the fileÕs title showing. This condition makes it very hard to make a precise composition. 

You should be aware that some programs cannot read EPS images 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.

Besides these four ÒuniversalÓ formats, there are also several file formats whose primary function is to compress graphics files: JPEG, GIF, and RIFF. There are other specialized formats for CAD, 3D, and animation files, but these are beyond the scope of this article.

Native formats. Understanding the standard file formats is only half of the battle. There are also all of the native, or proprietary, file formats. Take MacDraw for instance. A MacDraw Pro file saved normally goes in its own exclusive format. This picture can be easily read back into the MacDraw Pro program, but no other program can understand it. However, most graphics programs give you a choice of formats. You can use the ÒSAVE ASÉÓ command and choose the PICT format in MacDraw. This would allow you to open a MacDraw image in SuperPaint or Photoshop (for instance.) 

For many users, a page layout program will be the final destination for graphics. These folks will probably want to get all of their images into TIFF (bitmap) or EPS (object-oriented) files. This usually assures both maximum flexibility and the highest resolution.

Despite this apparent complexity, working with the Mac gives us the ability to do so much with graphics that a little study is definitely worthwhile. Experiment in order to find the format that works best in each instance.

By Jim Alley
© 1992 The Savannah Macintosh Users Group
---------------------------------------------
OPTIONAL CAPTION FOR (OPTIONAL) ILLUSTRATIONS
EPS files and PICT files can be resized without losing definition. This drawing was created with FreeHand and saved as an EPS file. It is reproduced above at 66% of its original size. Below, the same image cut from FreeHand and pasted onto this page. It has lost its EPS-ness and prints like a bitmap.
_________________________________________
The article above is reprinted from Mac Monitor, the newsletter of The Savannah Macintosh Users Group. It may be reprinted in a single issue of newsletters published by non-profit user groups. Payment shall consist of a single issue of the newsletter in which the article appears, sent to the following address:

Jim Alley
320 East 54th Street
Savannah, GA  31405