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Chapter 3. Working with Files in Illustr... > Determining File Format Requirements

Determining File Format Requirements

A file that's headed to the World Wide Web can be saved in one of several formats. Each format has its strengths and weaknesses. Images that are intended for four-color process printing can also be saved in several formats. There are, of course, several other possible destinations for your work. In this chapter, you'll look at appropriate file formats for those purposes, too.

More in-depth information on these specific issues is available in these chapters: Chapter 11, “Output Options”; Chapter 12, “Understanding and Applying Color”; Chapter 19, “Raster Images and Rasterized Objects”; Chapter 23, “Saving Images for the Web”; Chapter 24, “Flash and SVG Support”; and Chapter 25, “Commercial Printing and Trapping Issues.”

Raster Versus Vector

File formats can be divided numerous ways and into numerous categories. One of the most important divisions is between raster and vector. Although these concepts are explained at length in Chapter 19, it's important to have the most basic of understandings for this discussion of file formats. In a nutshell, a raster file saves an image as a series of pixels, colored squares arranged in a series of rows. Vector data, on the other hand, consists of mathematical descriptions of shapes. When raster images are resized (enlarged or made smaller), the images can become blurry. Vector images, on the other hand, remain sharp and clear at any size.

More and more, the line between vector and raster is blurring. Illustrator is a vector art program, but it can and does work with raster data. Adobe Photoshop, on the other hand, is a raster image editor. Photoshop 6, however, does have vector text capabilities and simulates vector objects through the use of clipping paths. Despite these advances, however, the difference between the two types of data is important.

If you're confused about the difference between raster and vector, see “Pixels and Paths” in the “Troubleshooting” section at the end of this chapter.

Web, Print, and Other File Destinations

For the Web, the most common file formats are all raster: JPEG, GIF, and PNG. Some of the newer formats, such as Flash and SVG, are vector based. JPEG is designed for photographs and also does a very good job with other continuous tone images. GIF, on the other hand, is limited in the number of colors it can store and so is better suited to images with large areas of solid color, such as clip art, cartoons, and logos. (The differences are explored in depth in Chapter 23.)

In the print world, EPS and TIFF can both be raster formats, although the clipping paths embedded in the files are actually vector data. Chapter 25 provides more information.

Illustrator also supports several other file formats, which are used specifically with certain programs. Files can be prepared in the native formats of programs such as Photoshop and AutoCAD, and for specific platforms and systems, such as Amiga and Pixar. Most files, however, are saved in a limited number of formats. They will be discussed later in this chapter.

Compression Issues

Many file formats shrink the amount of space required on disk for the file through compression. Files can also be prepared for archiving using compressed file formats. The two categories of file compression are lossy and lossless. Lossy schemes discard data to reduce file size. Lossless compression schemes rarely achieve the tiny file sizes available to their lossy counterparts but retain all of an image's original data.

The content of a file also plays a role in file format and compression selection. Some images are better suited for one type of compression than others; some files are better suited for a specific file type that uses one type of compression.

JPEG uses a lossy compression system, discarding data to reduce file size. There are several levels of JPEG compression, and Illustrator allows you to balance file size against image quality. The smaller the file, the more data discarded. The more data discarded, the lower the quality of the image.

Having trouble with JPEG? See “Lossy Compression” in the “Troubleshooting” section at the end of this chapter.

GIF and PNG usually use lossless compression schemes. All the image's original information is retained. New in Illustrator 9 is Save for Web's lossy GIF compression option.


Save for Web's option to reduce GIF file size by discarding data (Lossy %) cannot be used with the Interlaced option. Lossy GIF likewise is unavailable when Noise or Pattern dither is selected.

Platform Considerations

Filenames are still a consideration, despite the great strides that have been made over the past few years. The “eight-point-three” naming system is no longer required for Windows, but that doesn't mean that it's gone completely. (In computer jargon, “8.3” refers to a filename of up to eight characters followed by a period and a three-character file extension. This was and is the only acceptable way to name files in MS-DOS.)

The following are some considerations when you're naming files:

  • Windows filenames can be up to 256 characters long, and they are not case sensitive (upper- and lowercase letters are seen as the same letter). Several characters cannot be used in filenames: forward and back slashes, colons, asterisks, question marks, quotation marks, left and right angle brackets, and vertical slashes. In order, these characters are as follows: / \: * ? “ < > |

  • Macintosh filenames through OS 9 can be up to 31 characters long and are not case sensitive. The only forbidden character is the colon (:).

  • UNIX filenames can be 256 characters long, cannot use the slash character (/), and are case sensitive.

  • MS-DOS filenames can use only the 8.3 format and have the same character restrictions as Windows.

  • ISO 9660 for CD-ROMs uses the 8.3 name format and allows only 26 letters, the numbers from zero to nine, and the underscore (_). These names are not case sensitive. (This standard is designed to allow a CD-ROM to be recognized by any computer.)


When you're preparing files for the Web, including the three-character filename extension is important. Although the platform and operating system (OS) may support filenames without extensions, Web browsers require them. Because of the peculiarities of the Web, my best advice to you is to be as conservative as possible. Unless you have direct knowledge of (and control over) the server upon which your files will be stored, use the lowest common denominator for filenames:

  • Use the 8.3 naming convention and never forget to add the filename extension.

  • Stick with the 26 letters, the 10 numerals, and the underscore (_).

  • Use only lowercase letters.

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