Understanding and Choosing File Formats in Photoshop CS and Illustrator CS

Date: Apr 9, 2004

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In this chapter

Choosing a File Format

The Final Destinations

Photoshop's File Formats

Illustrator's File Formats

File Formats for InDesign

GoLive and File Formats

Mastering the Adobe Creative Suite

In this chapter, file formats are discussed, as are the various capabilities of each format and information on which format to select for which purpose. The information you learn here will help you determine an appropriate file format based on a file's final destination. You'll find a handy chart presenting the format capabilities and limitations of the major raster image formats. The chapter also offers an extensive discussion of how the JPEG file format compresses data, and the hazards of saving as JPEG multiple times.

Photoshop's new PSB file format for large images is presented here, as is the JPEG 2000 file format.

 

Choosing a File Format

Selecting the proper file format for your final artwork or project can mean the difference between having a usable document and a worthless collection of zeros and ones recorded to magnetic media. The file format should be determined by the image's final destination; for example, the Web has different requirements than do page layout programs. Even the Web design or page layout program you use can make a difference in what format to choose.

Within the broad categories of Web and print, additional choices need to be made. The file content will help you determine which format to choose.

Basic Concepts

Different file formats have different capabilities. Photoshop's native PSD format supports all the program's features. Some formats restrict the number of colors that can be used in a file (GIF and PNG-8, for example), and many don't support the CMYK color mode. The capability of portraying transparency with clipping paths and/or alpha channels also varies among formats. Vector type and vector paths can be supported in only a few file formats. Illustrator, InDesign, and GoLive—the other programs of the Adobe Creative Suite—all have their own file formats. The choice of format may require that you consider such features.

Generally speaking, working in a program's native file format until your project is complete is a good idea. You can then make a copy of the original file, saving in the required format. In Photoshop, for example, saving the original, with all layers intact, in unrasterized type, and in PSD format, gives you the most flexibility for future editing or repurposing of a file. Repurposing can be considered making another copy of a file in a different format, size, or color mode for a different purpose. For example, an image prepared as part of a print advertising campaign can be repurposed as a Web graphic for the advertiser's site.

It's also important to understand that file formats differ in how they record information. You can't change a file's format simply by going to Windows Explorer or the Mac's Finder and changing the three-letter extension at the end of a file's name; instead, you must resave or re-export the file to change the format.

You might also find that several file formats are appropriate for your end use and image content. Which one you choose could depend on factors beyond your control. For example, your service bureau or print shop might have a preference, or perhaps the intended audience for your Web site cannot be expected to have the plug-in required to see a particular format. However, in some cases, there is no difference between formats, and you're free to choose as you will.

Save, Save As, Save for Web, and Export

Generally speaking, the Save command updates a file on disk. The Save As, Save for Web, and Export commands are used to save the document in a file format other than its current format.

The primary methods of assigning file formats in Photoshop are the menu commands File, Save As and File, Save for Web. Illustrator relies heavily on the Export command to produce non-PostScript file formats. InDesign can create InDesign documents and templates with Save As, and it uses Export to generate PDF, EPS, and Web file formats (HTML, SVG, and XML). GoLive can export certain types of content as QuickTime movies, and you can export site diagrams as PDF or SVG files.

Save

If you create a document in Photoshop using the command File, New, the menu command Save is not available until a file format has been assigned by using Save As. Afterward, using the Save command updates the file on disk, maintaining the same format, if possible. If you've added layers or have otherwise changed the file so that it can no longer be saved in the original format, using the Save command opens the Save As dialog box. You have the option of changing to the Photoshop file format or saving the file as a copy.

In Illustrator, the Save command is available immediately after opening a new document. It simply opens the Save As dialog box.

Save As

Photoshop's Save As command can be used to create files in virtually any file format the program supports. Illustrator, in contrast, uses Save As to create only PostScript file formats and SVG. Illustrator's Export command generates other file formats supported by the program.

Any time you select a file format in the Save As dialog box that cannot support all the document's features, Photoshop defaults to saving a copy of the file. The As a Copy check box will be selected and grayed out to prevent deselection, the word copy will be appended to the filename (if the filename and format remain unchanged), and a warning message will appear at the bottom of the dialog box (see Figure 3.1).

Common triggers for the As a Copy warning are layers and transparency, which are supported by only a few file formats. When you see the warning, you have the option of saving the image as a copy or selecting a different file format from the Format pop-up menu. If you select a file format that does support the features of the image being saved, the warning disappears.

Figure 3.1 The image being saved contains layers, and the Pixar file format cannot support layers.

Photoshop's Save As command enables you to create files in a wide variety of file formats, suitable for a wide range of applications (see Figure 3.2).

Save for Web

Photoshop and Illustrator both offer Save for Web, which is (as the name implies) a Web-oriented tool and, therefore, is restricted to the Web-related formats. (The difference between Web and print formats is explained in the section "Web Versus Print," later in this chapter.) Save As can also be used to convert a file to a variety of Web-friendly formats, including JPEG and GIF. You cannot create a WBMP file using Save As.

For an in-depth look at Save for Web, see Chapter 22, "Save for Web and Image Optimization."

For more information on using Photoshop to prepare images for commercial printing, see Chapter 21, "Preparing for Print."

Figure 3.2 The Large Document Format option is not available in Save As unless that option is activated in Photoshop's File Handling preferences.

Export

Photoshop's Export command can generate paths for use with Adobe Illustrator. Using this command creates an Illustrator format file (AI). When the file is opened in Illustrator, it contains only the unstroked, unfilled paths. The paths can be used to create objects or perhaps as clipping paths to identify visible areas of an image.

Export can also create ZoomView files. ZoomView, from Viewpoint Corporation, is a sophisticated Web presentation technology that allows for quick downloading of interactive graphics. The viewer can zoom and pan within the graphic without any additional hardware. For information on obtaining a license to broadcast ZoomView files over the Internet, contact Viewpoint (http://www.viewpoint.com).

Illustrator uses the Export command to create rasterized versions of artwork, in a variety of file formats, and vector-based artwork for use with Macromedia's Flash, Microsoft Office, and AutoCAD, as well as legacy Illustrator and EPS files (see Figure 3.3). You can also export type from an Illustrator document as plain text (TXT).

Figure 3.3 These and other file format choices are explained individually later in this chapter.

Photoshop's Export Transparent Image Command

Another way Photoshop can assign a file format to an image is found under Photoshop's Help menu. The Export Transparent Image command walks you through the process of creating an image with a transparent background for use in a Web page or page layout document. You need answer only two questions, and an appropriate file is generated (see Figure 3.4).

Figure 3.4 If you click the I Need to Select the Area to Be Made Transparent radio button, you will be instructed to make the selection before returning to the assistant.

If the image is not already on a transparent background, you should make a selection of the area before selecting the menu command. Depending on your needs, the automated assistant generates an EPS file with a clipping path (for print) or a transparent GIF or PNG (for Web). After the file is created, the Save As dialog box opens. Do not change the file format in the Save As dialog box. The final file will have transparency defined as a matte (GIF) or by a clipping path (EPS).

Clear on the difference between transparency created with clipping paths or mattes and that generated with masks? If not, see "Hard and Variable Transparency" in the "Mastering the Adobe Creative Suite" section at the end of this chapter.

After you've saved the file created by the assistant, you'll be presented with a final dialog box. After clicking Finish, you can close the Photoshop file generated during the process. There's no need to save the file.

Photoshop's File-Handling Preferences

Several file-saving options can be set in Photoshop's Preferences dialog box. The top section of the File Handling pane, shown in Figure 3.5, enables you to determine what preview (if any) is saved with the file as well as whether the file extensions are added to the name automatically. (Windows requires the file extension and offers the choice of upper- or lowercase; Windows limits the Image Preview options to Always, Never, and Ask When Saving.)

Figure 3.5 The file extension is required for Windows, suggested for Mac OS X, and optional for Mac OS 9. Remember that many programs in which you place or view files require file extensions.

The File Compatibility section of the File Handling pane contains important options for file sharing and compatibility. Many digital cameras list sRGB as their color space when they actually capture a much larger color gamut. This inaccurate color profile tag can cause an image to be converted to that working space when opened in Photoshop. Because sRGB is a small gamut, this can adversely affect the appearance of the photo. Ignoring the sRGB tag in the EXIF data prevents this problem and has no effect on digital camera shots with other embedded profiles. (If your camera embeds another color profile, you can ignore this option.)

Photoshop can create TIFF files that include layers, which might not be usable by other programs. To avoid compatibility problems, Photoshop offers the option of reminding you when saving a layered file as a TIFF.

In versions of Photoshop prior to Photoshop CS, the maximum image size was 30,000 pixels by 30,000 pixels. That limit still holds for the Photoshop (PSD) file format. However, you can now work with images much larger than that. The new maximum pixel dimensions are 300,000x300,000 pixels. Files over 30,000 pixels in either dimension can be saved as TIFF (up to 4GB, the maximum size the TIFF standard supports) or Photoshop Raw (not to be confused with Camera Raw). There is also the option of using the new PSB file format—effectively a large-image version of the Photoshop PSD format. You activate the PSB file format capability in the File Handling pane of the Photoshop Preferences dialog box by checking the box Enable Large Document Format (.psb).

The PSB file format is discussed in greater depth later in this chapter. See "Large Document Format (.psb)."

The option to maximize Photoshop compatibility adds a flattened composite of the image, which increases file size (often substantially). The composite is used by early versions of Photoshop (4.0 and before) and by some programs that can place Photoshop files. If this option is turned off, you'll get a reminder when saving unflattened files (see Figure 3.6).

Figure 3.6 To turn off this warning, select Never in the Maximize PSD File Compatibility pop-up menu of the File Handling preferences.

Illustrator's File-Handling Preferences

The Files & Clipboard pane of the Illustrator Preferences dialog box offers a few options that affect the way files are saved (see Figure 3.7). You can elect to include the file format extension never, always, or have Illustrator present a dialog box each time you save a new file. The file extension can be forced to lowercase (for improved compatibility) using the Lower Case check box. Placed files that are linked to the Illustrator document can be updated manually, automatically, or you can have Illustrator present you with an update option when the linked file is modified. Illustrator's Files & Clipboard pane also offers the option of using a low-resolution image for linked EPS files. This option can speed screen redraw, but the proxy image won't be as detailed as the high-resolution version.

For more information on linked images, see Chapter 36, "Linking and Embedding Images and Fonts."

Figure 3.7 Guidelines for using file extensions with Illustrator are similar to those discussed for Photoshop earlier in this chapter.

Additional Considerations: Platforms and Compression

Although all the Web file formats and the major print-oriented formats are cross-platform (they can be viewed on both Macintosh and Windows computers), a number of the less common formats are primarily for use on one system or the other. In addition, such factors as filenaming conventions and media format could affect your ability to move a file from one operating system to another.

Windows requires each file to have an appropriate extension—a dot (period) and two- or three-letter suffix at the end of the filename. Lowercase extensions maximize compatibility. This extension identifies the file format and tells the operating system which program to use to open the file. Mac OS X prefers a file extension, but if a file or file type has been associated with a particular program, the file can still be opened by double-clicking. When no program is associated with a file or file type, a warning dialog box appears, and you're asked to pick an application for opening the file (see Figure 3.8).

Figure 3.8 The Mac OS X warning message is shown in this example. When you click Choose Application, the dialog box is opened for you.

Mac OS 9 requires no file extension. However, using extensions is a good idea. Even if you never plan on sharing the file(s) with anyone using a different operating system, eventually you'll upgrade to Mac OS X and want the files to still be usable.

File compression can also be an issue. Compression schemes available in a file format are either lossy or lossless. Lossy compression reduces file size, in part, by discarding image data. When the file is reopened, the missing data is reconstructed from the surrounding image information. Lossless compression maintains all the original data. JPEG uses lossy compression, on a sliding scale, and PNG and GIF use lossless compression. Lossy compression can result in substantially smaller file sizes, but at the cost of some image quality.

The compression supplied by a file format should not be confused with that available through utilities. Compressed archives can be produced by such programs as StuffIt and from within Windows (see Figures 3.9 and 3.10).

Zipped, stuffed, and other archived files must be uncompressed by the same or another utility before a program can open them. In the archive, the file retains the format with which it was saved. These types of file compression can be considered lossless—that is, they do not degrade the image quality.

Figure 3.9 Utilities such as StuffIt can produce a variety of compressed files.

Figure 3.10 Windows XP can compress files, folders, and drives in a variety of ways. The inset shows the icon for a "zipped" folder.

Filenaming Considerations

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 slashes (/), backslashes (\), colons (:), asterisks (*), question marks (?), quotation marks ("), left angle brackets (<), right angle brackets (>), and vertical slashes (|).

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

• Under Mac OS X, you can have filenames as long as 255 characters, and the colon (:) is the only forbidden character.

• 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 filename format and allows only the 26 letters, the numbers 0 through 9, and the underscore (_). These names are not case sensitive. (This standard is designed to allow a CD-ROM to be recognized by any computer.)

The Final Destinations

The vast majority of images created or prepared in Photoshop and Illustrator are destined for the World Wide Web or for print. The difference between the two is substantial, and you must consider the ultimate use of your image when selecting a file format.

Web Versus Print

The World Wide Web uses certain standards in an attempt to ensure that everybody can see everything in a Web page, as long as the viewer has a decent computer and a relatively recent Web browser. These standards include certain types of file formats for graphics so that all browsers can display images from the Web.

Page layout programs accept certain file formats that allow for the best reproduction of the image with ink on paper. Illustration programs that you use with Photoshop are able to create graphics for both print and the Web.

Because the requirements are different, and even the color mode differs between the Web (RGB) and print (CMYK), the file format you choose should depend on the image's final destination.

Generally speaking, the print file formats are TIFF, EPS, and PDF. For Web, Photoshop/ImageReady and Illustrator can produce GIF, JPEG, PNG, and WBMP files. Illustrator can also generate SVG and SWF files for the Web. In addition, a variety of other file formats are available for different purposes.

Commercial Printing Versus Inkjet Printers

Keep in mind that there's a huge difference between preparing an image for commercial printing and preparing an image for output to an inkjet printer. With the exception of those using a hardware or software RIP (raster image processor), inkjet printers require RGB color data. The overwhelming majority of inkjet printers are used with programs that do not support CMYK color. (CMYK color mode is available only in professional-grade graphics and layout programs.)

Another important difference is that images prepared in Photoshop that eventually are printed commercially are usually placed into a page layout program. Inkjet-destined images are typically printed directly from Photoshop. Additionally, inkjet printers can output virtually any file format created from Photoshop.

Photoshop's File Formats

Each file format that can be generated from Photoshop has its specific capabilities and intended purpose. Most offer one or more options as you save the file. Typically, a supplemental dialog box opens after you have selected a filename, format, and location in Save As.

Format Capabilities: The Overview

Different file formats have various capabilities. Table 3.1 shows a summary of the features of the most important file formats, along with those of some less-common formats for comparison.

The primary formats are discussed individually in the sections that follow.

¹ - In Photoshop, PSB is also referred to as Large Document Format.
² - Clipping masks are stored but not used by most other programs. Adobe InDesign does read the clipping path.
³ - Type and shape layers are rasterized if the file is reopened in Photoshop.
⁴ - Transparent background can be maintained in GIF.
⁵ - Files are saved as Photoshop Raw, but Photoshop CS is capable of opening Camera Raw files from most digital cameras.
⁶ - TIFF advanced mode preserves layers.

Photoshop CS ships with optional plug-ins for a variety of file formats that are not needed by the vast majority of Photoshop users (see Figure 3.11). Should you need to work with one or more of these formats, drag the plug-in into the File Formats folder of Photoshop's Plug-ins folder. The next time you start Photoshop, the file format will be available.

Photoshop (.psd)

Photoshop's native file format supports all the program's capabilities. Files in this format can be placed in the latest versions of InDesign and GoLive as smart objects and can be opened in Adobe Illustrator. This is the default file format. Most workflows (but not all) benefit from maintaining a file in Photoshop format until it's time to create a final TIFF, EPS, JPEG, or other file. It's also usually a good idea to maintain the original image, with editable type and layers, for future use.

Figure 3.11 Look for these plug-ins in the Optional Plug-ins folder, inside the Goodies folder, on the Photoshop CD.

When saving in Photoshop format, you can see that the Save As dialog box indicates which features are used in the image (see Figure 3.12). If a check box is grayed out, that feature is unused. If you uncheck a box, the file is saved as a copy. If you disable a feature (layers, for example) and save the image as a copy, when the image is reopened, that feature is gone—no more layers.

Figure 3.12 Selecting the As a Copy check box without changing other options simply appends the word copy to the original filename.

Large Document Format (.psb)

New in Photoshop CS is the capability of saving truly huge images. In earlier versions of Photoshop, the maximum image size was 30,000 pixels by 30,000 pixels. The new PSB file format can handle images as large as 300,000x300,000 pixels. Other than the maximum image size, the PSB file format is functionally similar to the PSD (Photoshop standard) file format.

Photoshop will remind you that the PSB file format is compatible only with Photoshop CS (see Figure 3.13). Other programs and earlier versions of Photoshop will not recognize the format.

Figure 3.13 Any file can be saved in the PSB format, but it won't be readable in any program other than Photoshop CS. That's another good reason to have this reminder.

CompuServe GIF

GIF is a common Web file format, suitable for illustrations and other images with large areas of solid color and no or few gradients or blends. Many logos and cartoons, as well as Web navigation items, such as banners and buttons, are appropriate for GIF. This file format is not appropriate for most photographs and other continuous-tone images because it can record a maximum of only 256 distinct colors. (A photograph might have thousands or millions of individual colors.) Although very small and adequately detailed thumbnails of photographs can be created as GIFs, a continuous-tone image typically suffers from posterization. When areas of similar (but not identical) color are forced into a single tint, the image quality can suffer severely.

The color table (the list of specific colors included in the image) is controlled through the Indexed Color dialog box. This box opens after you select the CompuServe GIF file format, a name, and a location for the file and then click OK.

For full information on the color options available for GIF files, see "Indexed Color," in Chapter 5, "Color, in Theory and in Practice."

Among GIF's capabilities are interlacing and animation. When a GIF image is interlaced, a Web browser displays every other line of pixels, first, and then fills in the balance of the image. This allows the Web page's visitor to see the image loading, giving the impression that progress is being made and that the image is loading faster. Animated GIFs are created in ImageReady.

Animated GIFs are discussed in Part IV, "ImageReady." See Chapter 23, "Creating Rollovers and Adding Animation."

The GIF format supports transparency in a limited way: A specific pixel can be opaque or transparent. You cannot have any pixels that are partially transparent in a GIF image. If the image is on a transparent background, you need only select the Transparency check box in the Indexed Color dialog box (see Figure 3.14).

You can also specify a color to be made transparent by using the Matte options in the Indexed Color dialog box. All pixels of the specified color then become transparent, regardless of location in the image. Dithering allows an image in Indexed Color mode to simulate more colors than are actually contained in the color table by interspersing dots of two or more colors.

GIFs can also be created with Save for Web. See Chapter 22, "Save for Web and Image Optimization."

The GIF standard is maintained by CompuServe, and software that creates or displays GIF images must be licensed by Unisys. (The licensing fee was paid by Adobe, and part of Photoshop's purchase price goes to the licensing.)

Figure 3.14 The Indexed Color dialog box opens automatically when you use Save As to create a GIF.

Photoshop EPS

PostScript is a page description language developed by Adobe, and it was at the heart of the desktop publishing revolution of the 1990s. An Encapsulated PostScript (EPS) file can contain any combination of text, graphics, and images and is designed to be included (encapsulated) in a PostScript document. EPS files contain the description of a single page or an element of a page.

EPS is typically used for elements to be included in a page layout or PDF document. Because PDF files can be designed for onscreen display as well as print, EPS supports the RGB color mode in addition to the CMYK and Grayscale modes. EPS files cannot be displayed by Web browsers (although they can be incorporated into PDF files, which can be shown through a browser plug-in).

One of the greatest advantages of EPS as a file format is the capability of including both raster and vector data and artwork.

To learn more about the difference between raster and vector images, see Chapter 4, "Pixels, Vectors, and Resolutions."

EPS supports all color modes, except Multichannel, and it does not support layers or alpha and spot channels. (The DCS variation of EPS supports both spot colors and masks and is discussed separately, later in this chapter.) The EPS Options dialog box, shown in Figure 3.15, offers several options.

The Preview option determines which image—if any—will be shown in the page layout program where you're placing the file. The preview doesn't normally have any effect on the printed image and is used for onscreen display only. Windows offers only None and TIFF as preview options. Here are the options offered by other platforms:

• None—No image preview is saved. Although Photoshop's File Browser can still generate a thumbnail, files placed into a page layout document may show on the screen as a box with diagonal lines.

• TIFF (1 bit/pixel)—A black-and-white (not grayscale) version of the image is shown in a page layout document.

• TIFF (8 bits/pixel)—A color version of the image is displayed onscreen in page layout programs. This option provides a reasonably accurate preview and is cross-platform.

• Macintosh (1 bit/pixel)—A black-and-white PICT preview is included with the EPS file. The PICT file format is designed for use on Macintosh systems but can be used for Windows programs as well.

• Macintosh (8 bits/pixel)—A color PICT preview is prepared.

• Macintosh (JPEG)—A JPEG preview is used, which can reduce the file size but also the compatibility.

Figure 3.15 Note in the Save As dialog box that the warning triangles indicate which features are not supported by the EPS file format.

The Encoding options include ASCII, Binary, and JPEG. ASCII is cross-platform and compatible with virtually all page layout programs. Binary is a Macintosh encoding system, and it can produce smaller files. JPEG encoding produces comparatively tiny files but uses lossy compression (which can result in image degradation) and is not compatible with all page layout programs. In addition, JPEG encoding can prevent an image from properly separating to individual color plates. ASCII is certainly the safest choice when the image will be sent to a printer or service bureau.

Halftone screens and transfer functions are established through the Print Preview dialog box. Screen frequency, angle, and shape can be established for each ink. These criteria determine the distribution and appearance of the ink droplets applied to the paper. The transfer function compensates for a miscalibrated imagesetter.

PostScript Color Management is available only for CMYK images outputting to devices with PostScript Level 3. This option should not be selected if the image will be placed into another document that itself will be color managed.

When the image contains unrasterized type and/or vector artwork or paths, select the Include Vector Data check box. When you're outputting to a PostScript device (such as a laser printer or imagesetter), the vector outlines will be preserved and the artwork will print more precisely. You need not include vector data when outputting to an inkjet printer.

Checking Image Interpolation allows a low-resolution image to be upsampled (resampled to larger pixel dimensions) when printed to a PostScript Level 2 or 3 printer. Increasing the resolution during printing helps smooth edges and improve the general appearance of low-resolution images, but this could introduce a slight out-of-focus appearance. If the output device isn't PostScript Level 2 or higher, this option has no effect.

For more information on upsampling, see "Two Types of Resampling," in Chapter 15, "Image Cropping, Resizing, and Sharpening."

JPEG

Joint Photographic Experts Group (JPEG) is technically a file compression algorithm rather than a file format. The actual file format is JFIF (JPEG File Interchange Format), although JPEG is more commonly used. JPEG supports Grayscale, RGB, and CMYK color modes and can be used with files more than four times as large as Photoshop's 30,000x30,000 pixel maximum. JPEG does not support transparency, alpha channels, spot colors, and layers. Paths can be saved with a JPEG file, including clipping paths (although most programs can't use the clipping path, with the notable exception of InDesign). Type is rasterized when a file is saved as JPEG.

JPEG is commonly used on the Web for photographs and other continuous-tone images in which one color blends seamlessly into another. Because of its support for 24-bit color (in RGB mode), JPEG is far better than GIF for displaying the subtle shifts in color that occur in nature. (Rather than GIF's maximum of 256 distinct colors, JPEG files can include more than 16.7 million colors.) JPEG is the most common file format for digital cameras because of the outstanding file size reduction capabilities.

When you choose JPEG as the file format and click OK, Photoshop's Save As dialog box is replaced with the JPEG Options dialog box (see Figure 3.16). You can select a matte color, a level of compression, and one of three options for Web browser display.

JPEG files can also be created with the Save for Web option. See Chapter 22, "Save for Web and Image Optimization."

Figure 3.16 The bottom of the dialog box shows the estimate of the amount of time it will take, under optimal conditions, for the file to download at a given modem speed at the selected quality setting.

Simulating Transparency in JPEG Files

Although JPEG does not support transparency, you can choose a matte color that will help simulate transparency in your image. From the Matte pop-up menu in the JPEG Options dialog box, choose a color that matches the background of the Web page into which the image will be placed. By replacing transparent areas of the image with the selected color (rather than just flattening to white), you cause those areas to match the Web page's background (see Figure 3.17).

Figure 3.17 The Photoshop image is shown at the top. To the left, it has been saved as a JPEG with a red matte and placed into a GoLive document with a red background. On the right is the image as it appears in a Web browser—a JPEG duck surrounded by "transparency."

Optimization Options

The cornerstone of the JPEG format is image optimization. The JPEG Options dialog box presents you with the tools to strike a compromise between file size and image quality. The Preview check box enables you to monitor changes to the image's appearance. The Image Options slider ranges from 0 (very small file, possibly substantial quality loss) to 12 (large file, very little—if any—damage due to file compression). The Quality pop-up menu offers Low (3), Medium (5), High (8), and Maximum (10) settings. Figure 3.18 shows a comparison of file sizes and file quality, using the duck image from the previous figure. The chart shows file format, compression type or level, and file size as reported by Mac OS X's Get Info command. (Different images might produce substantially

Figure 3.18 From left to right, the three images show JPEG quality settings of 12, 5, and 0. Note the substantial image quality degradation at the lowest quality setting.

Format Options

The Format Options section offers three JPEG format versions from which to choose:

• Baseline ("Standard")—This is the most widely compatible version of JPEG, which can be displayed by all graphics-capable Web browsers. It's also the version to use for non-Web JPEG files.

• Baseline Optimized—Optimized JPEG can produce better color fidelity but is not compatible with all older Web browsers.

• Progressive—Like interlaced GIF files, progressive JPEG files appear in stages in a Web browser, providing visual feedback and the illusion of speed to the Web page's visitor. You can elect to have the image appear fully in three, four, or five passes. (Three passes is usually adequate.) Progressive JPEG files are typically (but not always) slightly larger than baseline (standard) versions of the same files.

At the bottom of the JPEG Options dialog box is an area that shows the size of the file that will be created with the selected options as well as how long such a file will take to download. The pop-up menu enables you to select modem speeds ranging from 14.4Kbps to 2MBps.

JPEG/JFIF became an ISO standard in 1990. Baseline JPEG is in the public domain, but many variations are patented and licensed. Variations of lossless and near-lossless JPEG are under development.

Resaving JPEG Images

Because JPEG is a lossy compression scheme (some data is thrown away during compression), it's generally understood that files should be saved in the format only once (if at all). Resaving a JPEG file in JPEG format sends the image through the compression process again, possibly resulting in damage to the image's appearance because of the second round of data loss.

With the booming popularity of digital cameras, more and more images are being captured as JPEGs. Completely eliminating JPEG as a file format for resaving these images (and JPEGs created for the Web) after editing is unfeasible. To best understand how to avoid damaging an image when resaving it as a JPEG, you should know a little about how JPEG compresses.

Lossy compression, such as JPEG, can produce far smaller file sizes than lossless compression. That's because some image information is actually thrown away during the compression process. When the image is reopened, the existing data is averaged to re-create the missing pixels. However, the cost is image quality (see Figure 3.19).

To the left is the original. In the middle, saving at the highest quality produces little degradation. On the right, a JPEG Quality setting of 1 greatly reduces the quality of the image. Zooming in to 800% shows one key aspect of how JPEG works. In the low-quality version of the image, JPEG's distinctive 8x8 blocks of pixels are visible (see Figure 3.20). Colors can be averaged or patterns determined based on the content of the blocks.

Because JPEG uses blocks of pixels to compress an image, cropping becomes important. If you must crop an image that has already been substantially compressed with JPEG, any cropping from the top and left should be in increments of 8 pixels. Two copies were made of the image saved at JPEG Quality 1 (see Figure 3.21). One copy (left) was cropped exactly 8 pixels from the top and 8 pixels from the left. The second copy (right) had 4 pixels cropped from the top and left. Both copies were then resaved at JPEG Quality 1.

Figure 3.19 As you can see, the image on the right (saved at Quality 1) has a much degraded appearance compared to the original (left) and the image saved at Quality 12 (middle). However, the lower-quality image has a file size about one-third that of the higher-quality image.

Figure 3.20 An image is broken down into these 8x8 pixel blocks, starting from the top-left corner.

Perhaps the most precise way to crop an image in increments of 8 pixels is to use the Canvas Size dialog box. It not only allows you to specify an exact pixel size, but the Relative check box even eliminates the need to do math—select the check box and enter a negative number to reduce the canvas size (see Figure 3.22).

Another technique for preserving image quality when resaving a JPEG file as a JPEG file is to use exactly the same compression setting as originally used. If the original quality/compression setting is known, and if the image is being recompressed in the same program, then this technique is valid. However, keep in mind that different programs use different "scales" of JPEG compression. Saving a JPEG file at Quality 4 in Photoshop is not the same as saving as Quality 4 in Illustrator, nor is it the same as using 40% in Save for Web. Also, there is no set formula to translate between compression settings from a digital camera and Photoshop.

Figure 3.21 The image that was cropped in increments of 8 pixels (left) bears far more resemblance to the original (top). On the right, the image that was cropped in increments of 4 pixels looks much blurrier.

Figure 3.22 The grid, called the proxy, determines from where the canvas will be reduced or enlarged. If you're cropping from the center, remember to work in increments of 16 pixels (8 pixels for each edge).

When minimizing additional image degradation is important, consider resaving JPEG files at High or Maximum Quality, especially if the image has been cropped. The file size might be somewhat larger than the original JPEG, but quality will be maintained.

If you use a digital camera, a little experimentation can help you determine which quality setting you should use. In the example shown in Figure 3.23, the image in the upper right was taken at SQ (Standard Quality), which captures 640x480 pixels for this camera. To the left is the same scene, shot at HQ (High Quality), which produces an image 1,600x1,200 pixels, compressed at approximately the equivalent of using JPEG Quality 7 in Photoshop. The image in the lower right was shot at SHQ (Super High Quality), 1,600x1,200 pixels, minimal compression.

The two larger JPEG images are cropped to about 469KB when open in Photoshop. The original images as captured were 480KB (left) and 956KB (lower right). With the minimal difference in image quality and the substantial difference in file size between HQ and SHQ, for most purposes the more practical setting for this camera is HQ. Your camera may differ.

Figure 3.23 The two lower images are zoomed to 300%. The upper-right image, because of the smaller pixel dimensions, is zoomed to 700%.

Photoshop at Work: Controlling JPEG Compression

JPEG is an important file format when you consider the number of such images on the Internet and those taken with digital cameras. The lossy compression algorithm that JPEG uses is worth exploring. To practice controlling JPEG compression, follow these steps:

1. Open an image, any image, in Photoshop.

2. Use the menu command File, Save As and then select JPEG as the file format.

3. Use an image quality value of 0 and save the file to your desktop.

4. Close the open file and use the menu command File, Open to open the file you just saved.

5. Click the leftmost button at the bottom of the History palette to create a copy of the open image.

6. Save this copy, appending "-1" to the name. Again, use JPEG quality 0. Close and reopen the –1 file.

7. Position the two windows next to each other and zoom in 500% on an area of detail. Compare the two. Although neither looks good, they should be nearly identical.

8. Use the menu command Image, Canvas Size. Click in the lower-right corner of the proxy (the 3x3 grid labeled Anchor). Switch the unit of measure to pixels and then input a height and width, each 4 pixels smaller than the original value. Click OK.

9. Save the file as JPEG again, using the lowest quality setting.

10. Close and reopen the image.

11. Zoom in 500% and compare this version to the original.

You should see that saving the same image at the same setting doesn't cause much harm, but using a low compression setting after cropping an image that has already been compressed with JPEG can cause severe quality reduction.

JPEG 2000 (.jpf)

JPEG 2000, an improved variation of the JPEG file format, is now supported in Photoshop. Although this format is used for both print and the Web, most Web browsers require a plug-in to display JPEG 2000 images. You'll need to install the JPEG 2000 plug-in from the Photoshop CS CD to use this format.

Photoshop opens files in the extended JPEG 2000 format (JPF), but it can also create JPF files that are compatible with the JP2 format for JPEG 2000. (The file extension remains .jpf, regardless of whether the file is JP2 compliant or not.) The JPF format is more flexible than JP2, but fewer Web browser plug-ins are available. JP2 files will be 1KB larger than their JPF counterparts.

Among the advantages of JPEG 2000 over the earlier version of JPEG are transparency and lossless compression. You also have some control over what metadata is included with the file and how the image will appear in a browser as it downloads.

The JPF format supports RGB, CMYK, and Grayscale color modes, in either 8-bit or 16-bit color. Alpha channels, spot color channels, and paths are retained. Layers are merged when saved as JPF.

To create a JPF file, select the file format in the Save As dialog box, name the file, and choose a location. If desired, check the boxes to include the document's ICC profile (mandatory if JP2 compatibility is required) and spot or alpha channels. Then click Save. The JPEG 2000 window will open (see Figure 3.24).

Figure 3.24 More than just a dialog box, the JPEG 2000 window is reminiscent of a less-complex Save for Web window. You can resize the window by dragging the lower-right corner.

The JPEG 2000 window consists primarily of a large preview area to the left and settings options to the right. Here are the principle features of the JPEG 2000 window:

• Standard Zoom and Hand tools are available in the upper-left corner.

• The lower-left corner offers a zoom pop-up menu, with 10 preset zoom factors, ranging from 3.125% to 1600%.

• The File Size field enables you to select a target size for the file. This option is not available if lossless compression is used.

• The Lossless option prevents degradation of the image caused by lossy compression. Selecting Lossless will produce larger file sizes.

• Fast Mode improves the speed of the JPF file encoding, without harming the image. The File Size option is grayed out when Fast Mode is selected, although the actual file size can still be changed using the Quality slider or entering a value in the field.

• The Quality slider is used to determine the amount of compression applied to the file. It is not available when the Lossless box is checked because it controls only the lossy compression scheme. Like Save for Web, the Quality slider's values range from 1 to 100.

• You can elect to include metadata with the file. Depending on the choices made in the Advanced Options, you can include the image's metadata as XML (JPEG 2000 specific), XMP (Photoshop's File Info format), and/or EXIF data (from a digital camera).

• The image's ICC profile will be included, provided all three of the following boxes are checked:

• Embed Color Profile (in the Save As dialog box)

• Include Color Settings (in the JPEG 2000 window)

• ICC Profile (in the Advanced Options dialog box of the JPEG 2000 window)

• The Include Transparency option is only available when the image is on a transparent background. Layers will be merged upon saving, but the image will not be flattened.

• JP2 compatibility increases the file size by 1KB, but a wider variety of plug-ins will be able to open the file.

• The options accessed by clicking the Advanced Options button provide you with a choice of what types of devices you want the file to be compatible with (currently there is only one choice), the type of lossy compression "wavelet" you want to use, Integer (more consistent throughout the image) or Float (a bit sharper), the Tile Size setting (generally 1,024x1,024 is appropriate), the metadata format, and the type of ICC profile(s) to include (standard or the restricted profiles intended for cell phones and wireless devices). The Float compression scheme, available only for lossy compression, is useful for images with lots of fine detail, but it can create artifacts along edges. The tile size, which determines the areas of each "block" used for compression, is generally best left large. However, images for wireless Web access may benefit from a smaller tile size. Also, although the JPEG 2000 standard implies that a "restricted" ICC profile should be embedded in every JPF file, the devices for which the restricted profiles are intended (cell phones and PDAs) are not generally color managed...yet.

• As shown in Figure 3.24, you can specify how you want the image to display as it downloads using the Order pop-up menu. The options are Growing Thumbnail (a small image appears, then larger and larger versions of the image appear until the image is fully loaded), Progressive (the image starts fuzzy and then sharpens as it downloads), and Color (a grayscale version appears, which changes to color when the image is finished downloading).

NOTE

Keep in mind that if your image is not intended for the Web, the only significant options are in the JPF Settings section of the window.

• If the file contains one or more alpha channels, a channel can be selected as the "region of interest." The alpha channel determines what areas of the image require the highest quality. Because the Region of Interest option doesn't increase file size, all improvements within the region of interest result in decreased quality outside the region.

• The Enhance slider determines how much priority is given to the region of influence. The higher the level, the greater the quality within the area designated by the alpha channel (and the lower the quality outside).

• The Download Rate pop-up menu enables you to choose an Internet connection speed that will be "previewed" in the window. You can see how long it will take your image (nominally) to download over a connection of that speed in the field to the left, below the preview area.

• The Preview button shows you how your selected optimization order looks. Click the button, and the image will appear in the preview area as it would load into a Web browser.

Photoshop PDF

Adobe's Portable Document Format (PDF) is a cross-platform format that can be opened and viewed in the free Acrobat Reader, available for most computer operating systems. PDF is, at heart, a PostScript file format. Photoshop breaks PDF into two categories: Photoshop PDF and Generic PDF. Both can be opened, but only the former can be created.

Photoshop PDF supports all of Photoshop's color modes, transparency, vector type and artwork, spot and alpha channels, and compression (JPEG or ZIP, except for bitmap images, which use CCITT-4 compression).

The PDF Options dialog box, shown in Figure 3.25, offers a choice of compression schemes as well as several other choices.

ZIP compression is most effective for images with large areas of solid color, and it is also more reliable than JPEG for PDFs that are destined for process printing. (PDFs compressed with JPEG might not separate correctly.) JPEG, however, can produce substantially smaller files (at the cost of image quality).

Figure 3.25 After you select a filename, location, and Photoshop PDF as the file format, clicking OK opens this dialog box.

Photoshop also enables you to use standard PDF security, such as that added to PDFs in Adobe Acrobat (see Figure 3.26). Passwords can be required for opening the document as well as for printing, selecting, changing, copying, or extracting the document's content.

Figure 3.26 Other check boxes in the PDF Security dialog box are made available if they pertain to the file being saved.

PNG

Developed as an alternative to GIF and JPEG for the Web, Portable Network Graphics (PNG) comes in both 8-bit (Indexed Color) and 24-bit (RGB) variations. JPEG's lossy compression and the licensing requirement associated with GIF's compression lead to the demand for an alternative. PNG-8 and PNG-24 are both now widely supported by Web browsers.

The Save As dialog box makes no distinction between PNG-8 and PNG-24, instead using the file's existing color mode. If the image is RGB, PNG-24 is automatically created. If the image is Indexed Color, PNG-8 is used. Grayscale is also 8-bit. (Save for Web allows you to specify whether you want to create an 8-bit or 24-bit PNG file.) Because PNG does not support CMYK, it is not appropriate for commercial printing applications.

Like interlaced GIF and progressive JPEG, PNG files can also be displayed incrementally in a Web browser. After you select the PNG format, name, and location and then click OK, the PNG Options dialog box enables you to make the selection (see Figure 3.27).

Figure 3.27 Interlacing can add slightly to the file's size. It's not necessary with small interface items but is often appropriate for larger images.

Images in Indexed Color mode are comparable in size and appearance when saved as GIF and as PNG-8. PNG-24 cannot match the file size reduction available in JPEG; however, the format does offer transparency (which is not available at all in JPEG) and uses a lossless compression algorithm, thus preserving image quality.

Raw

In Photoshop, it's necessary to differentiate between Raw files saved from the program (Photoshop Raw) and digital camera files being opened in the program (Camera Raw). Many high-end cameras use proprietary versions of the Raw format. Previous releases of Photoshop could not natively open such files. The various camera manufacturers had their own software to open and process the files, from which you could save a TIFF file to open in Photoshop. In early 2003, Adobe released a Photoshop 7 plug-in called Camera Raw for use with the top cameras from Canon, Nikon, Minolta, Olympus, and FujiFilm. That plug-in has been incorporated into Photoshop CS and has some additional capabilities.

Photoshop Raw

The Photoshop Raw file format records pixel color and very little else. Each pixel is described in binary format by color. Because the file doesn't record such basic information as file dimensions and color mode, coordination and communication are important. If incorrect data is entered into the Raw Options dialog box when an image is opened, an unrecognizable mess is likely to result (see Figure 3.28).

When saving an image in the Raw file format in Macintosh, you can specify the four-character file type, the four-character creator code, how many bytes of information appear in a header before the image data begins (if any), and in what order to save the color information (see Figure 3.29). When interleaved, color information is recorded sequentially for each pixel—the first pixel's red, green, and blue values are followed by those three values for the second pixel, and so on. The sequence is recorded as R,G,B, R,G,B, R,G,B.... Noninterleaved order records the red values for all the pixels, then the green values for the pixels, and then the blue values. The sequence is then R,R,R... G,G,G... B,B,B....

Figure 3.28 In the upper left, the image was opened properly. To the right, the Interleaved option wasn't selected. Below, the dimensions were incorrect. If the number of channels or the bit depth is wrong, you'll see a warning that the file size doesn't match.

Figure 3.29 Before saving a file in the Raw format, make sure you know and understand the requirements for the program in which the file will be opened.

Camera RAW

When you select and open an image from a high-end digital camera, Photoshop will, if necessary, launch the Camera Raw plug-in. (Some Raw files can be opened directly in Photoshop.) The Camera Raw plug-in offers very powerful image-adjustment capabilities. Global color and tonal adjustments, sharpening, noise and moiré reduction, and compensation for color fringing caused by chromatic aberration are some of the features of Camera Raw.

TIFF (.tif)

Tagged Image File Format (TIFF) and EPS are the two most widely accepted image formats for commercial printing. TIFF files can be produced directly by most desktop scanners and many digital cameras. The format supports CMYK, RGB, Lab, Indexed Color, Grayscale, and Bitmap color modes. In Bitmap mode, alpha channels are not supported, but they are available in all other color modes. Spot channels are supported, and clipping paths can also be saved with TIFF images to denote areas of transparency.

Photoshop offers a variety of TIFF options, some of which are not supported in other programs. Background transparency, layers, and JPEG compression are three. Additional TIFF options are found in the TIFF Options dialog box, which appears following the Save As dialog box (see Figure 3.30).

Figure 3.30 Some options in this dialog box might be grayed out and unavailable, depending on the image's content.

For maximum compatibility, choose LZW as the compression scheme. ZIP and JPEG are not supported by many programs that use TIFF files. JPEG offers the same 0–12 scale of quality available in the JPEG Options dialog box.

The Byte Order option determines compatibility with Macintosh or IBM PC computer systems. Because the Mac has no trouble reading the IBM version of TIFF files, that is the safest choice.

Although Photoshop itself doesn't read a TIFF file's image pyramid, the multiresolution data can be saved for other programs, such as InDesign. Image pyramid refers to multiple versions of the same image being stored in one file, each at a different resolution. Photoshop reads only the highest- resolution version of a TIFF file.

If the file contains background transparency, you can elect to save that transparency. As with other advanced TIFF features, the transparency option is not widely supported for TIFF files; however, it is supported by InDesign 2.0. (Remember that this transparency refers to the entire file, not layers above a background layer.)

When a file is saved with layers, you have the option of determining how those layers will be compressed. Because layers can greatly increase file size, ZIP may produce substantially smaller files. You can also choose at this point to disable layers in the TIFF file and save as a copy. In terms of the resulting file, there is no difference between discarding layers (flattening the image) with this option and unchecking the Layers check box in the Save As dialog box.

Because not all other programs can read a TIFF file's layers, Photoshop saves a flattened version of the image as well. Saving layers in TIFF file format triggers a warning message from Photoshop (see Figure 3.31). Because a flattened version of the image is also saved in the TIFF file, the warning can be ignored.

Figure 3.31 If your image is to be used in a program that doesn't support layered TIFF files, discarding the layers can greatly reduce file size with no loss of functionality.

Photoshop DCS

Desktop Color Separations (DCS) is a version of EPS developed by Quark. (The file that's produced has the .eps extension.) The original DCS file format is now referred to as DCS 1.0, whereas an updated, more flexible version is called DCS 2.0.

Photoshop DCS 1.0

Version 1.0 should be used only with older programs that don't read the DCS 2.0 standard. DCS 1.0 supports CMYK and Multichannel modes and creates a separate file for each color channel, plus an optional 8-bit color or grayscale composite. The DCS 1.0 Format dialog box appears after you click OK in the Save As dialog box (see Figure 3.32).

Figure 3.32 These options determine compatibility with page layout programs.

You can elect to save no preview, a 1- or 8-bit TIFF preview, and in Macintosh, a 1- or 8-bit Macintosh (PICT) preview or a JPEG preview. The 8-bit TIFF preview is the most widely supported. In addition to the preview, which is used primarily in dialog boxes, you have the option of including a grayscale or color composite image or no composite at all. The composite is used to show the image when a page layout document is viewed onscreen.

The encoding options include Binary, ASCII, and JPEG. As with EPS files, ASCII is used in Windows and can be read by Macintosh programs, Binary produces smaller files but is Mac specific, and JPEG reduces both file size and compatibility. In addition, JPEG encoding can prevent an image from properly separating to individual color plates. ASCII is certainly the safest choice when the image will be sent to a printer or service bureau.

The Print Preview dialog box offers access to halftone screens and transfer functions for the file. These criteria determine the distribution and appearance of the ink droplets applied to the paper. The transfer function compensates for a miscalibrated imagesetter. Do not make changes to the screens or include a transfer function without explicit guidance from your printer or service bureau.

Photoshop DCS 2.0

DCS 2.0 is a more sophisticated version of Desktop Color Separations. The majority of its options are the same as those described for DCS 1.0. However, DCS 2.0 gives you several options when it comes to what file or files are actually produced (see Figure 3.33).

Figure 3.33 The six Preview options boil down to one file or one file for each channel and a choice of composite image.

If you choose any of the three Multiple File options (no composite, grayscale composite, color composite), one file is generated for each color channel. The four process channels (if present in the image) use the channel's letter for a file extension. Spot channel extensions are numbers, starting with 5. The composite, if generated, will have the .eps extension.

For example, the file "Target" with two spot channels could be saved as DCS 2.0, with multiple files and a color composite. The files generated would be Target.C, Target.M, Target.Y, Target.K, Target.5, Target.6, and Target.eps.

DCS 2.0 should be selected over DCS 1.0 in any circumstance where both are supported. The single file saves disk space and can simplify file exchange and handling.

Illustrator's File Formats

Illustrator uses the Save As command to create AI (Illustrator), EPS, PDF, and SVG files. The Export command offers 15 additional file formats, including AI and EPS, compatible with earlier versions of Illustrator.

Illustrator CS can open files in more than two dozen formats, in more than 50 different versions. The full list is shown in Figure 3.34. (Keep in mind that not all features of all formats are preserved in Illustrator.) The default (All Readable Documents) shows all files Illustrator can open. Selecting a specific format can make it easier to find the file you need.

Figure 3.34 This is the Show pop-up menu from Illustrator CS's Open dialog box.

Placing Files into Illustrator Documents

One of the two ways that you can place artwork in an Illustrator document from another file is linking. A linked image remains separate from the document to which it is linked. This is somewhat similar to a hyperlink for the Web; only a pointer is placed in your illustration, and the external image is loaded when your file is opened. Illustrator notifies you if any changes have been made to the original. Keep in mind, though, that your image must always be able to find the external artwork. If you were, for example, to send out your image on disk without including a copy of the linked file, the linked artwork would not be available to anyone opening your image from the disk—a warning dialog box would appear. The Save As command (and Save the first time it is used) allows you the option of including linked files.

Embedding is the other way to include artwork from another file in an Illustrator document. When you embed an image, a copy of the artwork is incorporated into your Illustrator document. You are not notified of any changes to the original artwork, and the only way to update the embedded image is to replace it. The advantage is that the placed artwork becomes part of your Illustrator document, and it doesn't have a link that can be accidentally broken. The Illustrator document's size increases by the size of the placed artwork.

Illustrator can place files of any format that it can open, with the exception of the Illustrator (AI) format. The formats in the following list, however, must be embedded rather than linked:

• CGM

• DOC

• DXF/DWG

• Freehand

• RTF

• SVG

• WMF

File Formats Available Under Save As

The Save As dialog box offers six file formats from which to choose:

• Adobe Illustrator Document (.ai)—This is the native file format for Adobe Illustrator. It supports all the features of the program. However, earlier versions also use the .ai file extension and do not support all the features of Illustrator CS.

Illustrator offers you several options when saving a file in its native format. You can see them in the dialog box shown in Figure 3.35.

Figure 3.35 After you select a name and location for a file and click OK, this dialog box opens.

• Illustrator EPS (.eps)—PostScript is a page description language developed by Adobe. Encapsulated PostScript (EPS), like PDF, supports both vector and raster information. EPS is often used to put a graphic element into a page layout program. Typically, the EPS file is an image on a page, but it can be a complete page as well.

EPS files can contain previews that are visible in a page layout program. When no preview is present, a placeholder (a box with two crossing diagonal lines) is shown on the page. Macintosh previews are available in PICT (Macintosh) or TIFF format, and either can be 1-bit (black and white) or 8-bit (color). Windows EPS files can have previews in TIFF or Windows Metafile (WMF) format.

In addition to choosing the file format, you can opt to have transparency for TIFF previews in the EPS Format Options dialog box (see Figure 3.36).

NOTE

Remember that you use the Export command in Illustrator CS to create Illustrator documents compatible with earlier versions of the program.

TIP

Because TIFF previews are compatible with both Windows and Macintosh, you should choose this option when saving as an EPS file. Also, although the 8-bit color preview will increase the file size slightly, you should choose it rather than the 1-bit black-and-white version.

Figure 3.36 Illustrator CS gives you greater control over EPS images than did prior versions.

• Illustrator Template (.ait)—Templates can be created to give you a head start on recurring projects or layouts. Illustrator CS ships with over 200 ready-made templates (inside the Illustrator folder, in a folder named Templates). You can also create custom templates to fit your work. Open or create a document, set it up the way you want things to be when you start a similar document, and save it as an Illustrator template. When you open a template, you're creating a new, untitled Illustrator document. Think of templates as unlimited custom Startup files. Here are the customizable features of templates:

• Artboard and document sizes and layouts.

• The opening document view, including zoom, position of the artboard in the window, and ruler point of origin.

• View menu options, including guides, rulers, and the various Show/Hide choices.

• Palette contents. You can add (or delete) any swatches, symbols, brushes, styles, and Actions.

• You can add any artwork to the artboard that you want to include in any project you start with this template—copyright information, the company logo, even artwork you'll use only sometimes. (After opening the template, you can delete any default artwork.)

NOTE

Like the Illustrator file format, EPS files compatible with earlier versions of Illustrator are created with the Export command.

NOTE

The Illustrator template format also generates two new commands in the File menu: Save as Template (which is the same as using the Save As command and selecting Illustrator Template as the file format) and New from Template (which is the same as using the Open command and selecting a template). These two commands are simple conveniences that can be very handy when working with templates.

• Illustrator PDF (.pdf)—The native format of Adobe Acrobat, PDF files are now very common. Acrobat Reader can be found on most modern computers and is freely available for others. Documents saved in PDF format can be viewed on almost any computer.

PDF files support both vector and raster (bitmap) information. Although PDF pages are PostScript at heart, they can also contain annotations and notes and can be searched and hold hyperlinks.

Illustrator CS's PDF Options dialog box offers five panels of options, most of which are comparable to Acrobat's options. You can select ODF security, image compression and downsampling, font embedding and subsetting, and ICC profile embedding. You can also specify printer's marks and bleeds. What's more, when Acrobat 6 compatibility is selected, you have the option of creating PDF layers from the top-level Illustrator layers.

TIP

Before saving complex illustrations as PDF files, you can take an extra step to help preserve the appearance of your image and ensure problem-free printing. Working on a copy of your original, open the Layers palette. From the palette menu (the little triangle in the upper-right corner of the palette), select Flatten Artwork. You can then save the file in PDF format with its original appearance intact.

• SVG (.svg)—Scalable Vector Graphics files are used on the World Wide Web. When saving in this format, you have the option of including part of a font or the entire font. Any placed images can be embedded or linked. You can retain the capability of editing the image in Illustrator if necessary. When you click the Advanced button, you'll see the additional options shown in Figure 3.37.

Figure 3.37 The SVG Options dialog box contains an Advanced button that opens the additional dialog box.

• SVG Compressed (.svgz)—The options for this file format are identical to those for the standard SVG format. The compressed version of the format is not supported by all SVG plug-ins.

Export

In addition to the three primary file formats and SVG available in the Save As dialog box, Illustrator offers a variety of export formats. The default file formats that you can create with the Export command are shown in Figure 3.38.

Figure 3.38 Any of these formats you are unlikely to ever need can be deleted from the Photoshop Formats folder, found within Illustrator's Plug-ins folder.

A number of Illustrator's export formats require rasterization (conversion to pixels) before you save the file. The Rasterize Options dialog box is shown in Figure 3.39.

Figure 3.39 CMYK, RGB, Grayscale, and Bitmap color modes are supported, depending on the selected file format, as well as choices of resolution and antialiasing.

Here is a list of the formats, presented in alphabetical order:

• AutoCAD Drawing (.dwg)—AutoCAD is a premier architectural and engineering design tool. DWG is the program's standard vector file format. DWG (and its sister format, DXF) swaps white fills and strokes for black. The DXF/DWG Options dialog box is shown in Figure 3.40.

• AutoCAD Interchange File (.dxf)—This file format is used to exchange information between AutoCAD and programs that do not support the DWG format. From Illustrator, it can also be used to exchange information with those programs. When you're working directly with AutoCAD, however, DWG is usually a better choice. DXF is a tagged format. The dialog box is identical to the one shown in Figure 3.40.

• Bitmap (.bmp)—BMP requires that an image be rasterized before you save it. The Rasterize Options dialog box offers RGB, Grayscale, and Bitmap color modes. In addition, the BMP Options dialog box offers compatibility with Windows or IBM's OS/2 format, a choice of color depth, and (in some cases) compression (see Figure 3.41).

Figure 3.40 AutoCAD version, bit depth, and raster format for fills and textures are among the choices for the DWG format.

Figure 3.41 The Run Length Encoding (RLE) compression option is not always available.

• Enhanced Metafile (.emf)—An advanced version of Microsoft's Windows Metafile (.wmf) format, EMF is available only for 32-bit Windows. The export function has no user-defined options.

• Illustrator Legacy (.ai)—You can create AI files compatible with earlier version of Illustrator using the Export command. You can generate files suitable for Illustrator 10, 9, 8, and the English and Japanese versions of Illustrator 3. The options shown in Figure 3.42 will vary, depending on which version is selected in the pop-up menu at the top.

• Illustrator Legacy EPS (.eps)—Just as you use the Export command to generate Illustrator files compatible with earlier versions of the program, so, too, do you use Export to create legacy EPS files. The options are shown in Figure 3.43.

• JPEG (.jpg)—One of the two main file formats on the Web, JPEG is a 24-bit file format best suited for photographs and other continuous-tone images. In addition to Export, JPEG is available through Illustrator's Save for Web feature. The JPEG Options dialog box, shown in Figure 3.44, offers choices of quality/file size, (using a scale of 1 to 10), baseline or progressive downloading, image resolution, antialiasing, ICC profile embedding, and image map management (for Internet links). More information is available in Chapter 37, "Illustrator and the Web."

NOTE

The term bitmap is used generically to refer to any raster image and can also be used to refer to the 1-bit color mode, in which every pixel is either black or white. To avoid confusion, the file format is generally referred to as "BMP."

Figure 3.42 The Transparency section of the dialog box is used only for versions of Illustrator that do not support transparency natively.

Figure 3.43 This dialog box is a hybrid of the EPS Options and the Illustrator Legacy Options dialog boxes.

• Macintosh PICT (.pct)—PICT supports both raster and vector artwork. However, should you reopen a PCT file in Illustrator, you may find that the vectors have not been preserved in the original format. Don't export to PICT if you intend to further edit the artwork later.

• Macromedia Flash (.swf)—Although not the native Flash format, SWF fulfills the need for a vector-based, interactive file format. SWF is actually the Shockwave file format. (Flash's FLA is a proprietary format controlled by Macromedia.) SWF is a Web format, but viewers must use a browser equipped with the Flash plug-in. Figure 3.45 shows the dialog box for Flash (SWF) Format Options.

Figure 3.44 Download method and image map management are relevant only to images destined for the Web.

Figure 3.45 You can export the image as a single SWF file, a series of animation frames, or as a series of SWF files.

• Photoshop (.psd)—Layered Illustrator documents can be exported to Photoshop with layers intact. You can choose compatibility with recent versions of Photoshop, or you can export a file that can be read by Photoshop 5.5. You have the option of color mode (RGB, CMYK, or Grayscale), resolution, and whether to flatten layers or retain them. Figure 3.46 shows the Photoshop Export Options dialog box.

• Portable Network Graphics (.png)—The PNG file format is a raster image format used on the Web. It offers lossless compression to preserve image quality. When exporting a file as PNG from Illustrator CS, you can specify resolution and either a transparent background or a colored background (see Figure 3.47).

Figure 3.46 With layers and editability selected, "type on a path" can be edited in Photoshop CS (but not previous versions).

Figure 3.47 Selecting Other as a background color opens a small Color Picker that enables you to match the background of a Web page.

• Targa (.tga)—Targa files can be used with digital video programs, such as Adobe Premiere and AfterEffects. Artwork is automatically rasterized (refer to Figure 3.39) when saved as Targa. TGA supports RGB and Grayscale color modes.

• Text (.txt)—This "plain text" format is a most basic text format. It is a suitable choice when you need to move text to a word processor without fancy formatting. Such options as baseline shift and character scaling will be ignored.

• Tagged Image File Format (.tif)—TIFF (as the file format is known) is among the most common raster image formats. In addition to image-editing programs, many scanners produce TIFF files. This format is among the most common for placing rasterized images into page layout programs. In addition to the settings shown in the Rasterize Options dialog box (refer to Figure 3.39), the TIFF options include LZW compression settings and ICC profile embedding.

• Windows Metafile (.wmf)—The basic file format of clip art from Microsoft Office for Windows (among other programs), WMF is a vector format. There are no options for exporting to WMF format.

File Formats for InDesign

When discussing file formats for use with InDesign, we need to consider three aspects of the program: What formats can be opened by InDesign? What types of files can be placed into an InDesign document? What file formats can be generated (output) by InDesign?

Opening Documents and Templates in InDesign

InDesign, naturally, opens its own documents and templates. InDesign documents use the file extension .indd, templates use the extension .indt, and InDesign books have the file extension .indb.

The Open a File dialog box, shown in Figure 3.48, offers the option of Open Normal, Open Original, or Open Copy. Generally speaking, Open Normal is the appropriate choice. Open Original is used to edit a template, and Open Copy automatically creates a duplicate of the selected file, leaving the original unchanged. (To create a new document from a template, use Open Normal.)

Figure 3.48 The Show pop-up menu offers the choice of All Readable Documents or All Documents.

In addition to InDesign's own documents and templates, you can open documents and templates from PageMaker (version 6.5 or later) and QuarkXPress (version 3.3 or later). Note that InDesign does not support Quark XTensions. Any graphic added with an XTension won't display or print properly.

InDesign also uses the Open command to open Object Libraries. Object Libraries are collections of graphic elements, pages, text, guides and grids, and shapes. When opened, these elements appear in a palette, ready to be added to the open document. InDesign library files use the file extension .indl.

Placing Files into InDesign Documents

Although it certainly is possible to copy/paste or drag/drop to add graphics to an InDesign document, the most reliable method is the File, Place command, which enables you to control resolution, color, and some format-specific characteristics of graphics. (You can also use Place to add a text file to your document.) Figure 3.49 shows a list of those file types generated by Photoshop and Illustrator that can be placed into an InDesign document. Note the Show Import Options box. This option, by default, is not selected, although it gives you greater control over the artwork being added to the document.

Figure 3.49 Among the file formats you cannot place into InDesign are JPEG 2000, Raw, and Photoshop's Large Document Format (PSB).

Of the file formats that you can place into an InDesign document, there are only a few that you should place. Such formats as PICT, PCX, and WMF may be suitable for output to low-resolution inkjet printers, but they are not acceptable for commercial printing presses. Here are some points to remember when placing files in an InDesign document:

• Photoshop, Illustrator, PDF, EPS (and the derivative format DCS 2.0), and TIFF should be the first choices.

• For documents that will eventually be posted on the Internet, JPEG, GIF, and PNG can be used.

• WMF and EMF files can be opened in Illustrator and saved as Illustrator, PDF, or EPS files.

• BMP, PCX, PICT, and SCT files can be opened in Photoshop and saved as Photoshop, PDF, EPS, or TIFF files. All except Scitex (SCT) can also be opened in Illustrator and saved or exported in a preferred format.

Import Options for Placed Graphics Files

When the Show Import Options box is checked in the Place dialog box, placing Photoshop, TIFF, JPEG, GIF, BMP, PCX, and SCT files gives you the options shown in Figure 3.50. You can apply a clipping path (if one is embedded in the image) and elect how to color-manage the document (when ICC profiles are available).

Figure 3.50 When no clipping path or ICC profile is available, the Image Import Options dialog box does not appear.

The PNG file format includes one additional set of options, shown in Figure 3.51. If transparency has been designated in the image with an alpha channel or a specified color, you can use that information in InDesign. Gamma correction can adjust the tonality of an image to match that of a non-PostScript printer.

Figure 3.51 Remember that the PNG file format does not support CMYK color. PNG images will not separate.

The Illustrator and PDF file formats enable you to crop, preserve halftone screen information, and retain transparency in a placed image. The Place PDF Options dialog box is shown is Figure 3.52.

Figure 3.52 Because the Illustrator (AI) file format is based on PDF, it shares the Place PDF options.

If Show Import Options is selected when placing an EPS or DCS file, you'll see the dialog box in Figure 3.53. If a low-resolution proxy is embedded in the image, you can elect to use that for onscreen display by checking the Read Embedded OPI Image Links box. (Although a low-resolution version of the image will appear on the monitor, the actual high-resolution image will print.) If saved with the file, a clipping path can be used. You also have the choice of using an embedded TIFF or PICT preview or having InDesign generate a preview from the actual image data.

Figure 3.53 The proxy appearance has less to do with these options than it does with your choice of Optimized Display, Typical Display, or High Quality Display in InDesign's View menu.

When placing PICT, WMF, and EMF files, you have no Options dialog box.

Saving and Exporting InDesign Documents

When you use the Save command, InDesign creates (the first time) or updates (during subsequent saves) an InDesign document. The Save As command offers the option of saving as a template. You can also use Save As to assign a new name to the file, thus creating a copy. The Save a Copy command makes a copy of the file, document, or template and appends "copy" to the name.

InDesign's Export command enables you to save the document in a variety of formats. PDF and EPS are available for print-related projects. PDF, HTML, SVG, and compressed SVG are available for Web projects. InDesign can also generate XML, which is handy for projects that require multiple destinations, such as print, the Web, and PDAs.

GoLive and File Formats

GoLive opens Web pages and Web sites created in GoLive, as well as HTML (and related) documents generated by other programs. It can work with text files and graphics in a variety of file formats. GoLive also takes advantage of Adobe's Smart Objects technology, which enables you to place artwork from Illustrator, Photoshop, or LiveMotion directly into the GoLive page. GoLive optimizes the file for the Web and stores the optimization information. Should the source file be changed, GoLive can quickly and easily update the Web page. You can double-click the image in GoLive to launch the parent application and edit the file.

Although the standard graphics formats for the Web are JPEG, GIF, and PNG, GoLive can work with a variety of other formats as smart objects. Photoshop (PSD), Illustrator (AI), LiveMotion (LIV), PDF, TIFF, and EPS files can all be used. In addition, less-common file formats are available, including Amiga IFF, BMP, PCX, PICT, Pixar, and Targa.

Scalable Vector Graphics (SVG) and Flash (SWF) files can also be used in GoLive. SVG files can be generated in Illustrator, and both Illustrator and LiveMotion can produce SWF files.

Mastering the Adobe Creative Suite

Formats and Platforms

What makes .tif or .psd files different in Macintosh and Windows?

Actually, nothing. A file extension indicates a particular file type. File types are almost always standardized so that they work equally well on both Windows and Macintosh computers (assuming that the appropriate program is available). However, the file must be on a disk or drive that can be read by the computer. Macintosh computers can read and write Windows-formatted disks, but Windows computers can't read Mac-formatted disks without a utility.

Remember, too, that file formats can change with versions of the software. Just as a PSD file created by Photoshop can have features that cannot be used in Photoshop 4, so, too, do the most recent DOC files from Microsoft Word have features unavailable in Word 4.2.

Hard and Variable Transparency

I want a soft drop shadow around my image, but Export Transparent Image always seems to leave a white halo below the shadow.

The transparency generated for EPS and GIF files is hard-edged transparency, in which a pixel is either completely transparent or completely opaque. Your drop shadow relies on variable transparency, in which pixels can be partially transparent.

Save for Web can now generate GIFs with dithered transparency, interspersing opaque pixels and transparent pixels. Print applications are a good bit trickier. InDesign 2.0 supports variable transparency, but other page layout programs do not. There are various techniques for simulating such effects as drop shadows, but generally it's easier to replicate the page's background in Photoshop.

Lossy Compression

I want to get my files really small for the Web, but it takes a long time. I save an image at one compression level and open it up to look at it. Then I have to go back and try a different compression level to get what I want. Isn't there a way to preview an image being saved as a JPEG?

Use the menu command File, Save for Web. This feature allows you to compare up to four versions of the same image, all at the same time. You pick the versions that best meet your needs for quality and file size and then click OK.

RGB for the Web

I created JPEG files of a lot of the images my company used in its latest brochure so that I could post them on the Web, but they don't show up. I exported them as JPEGs, so what's the problem?

For a brochure, eh? I'll bet those images were CMYK. Although that color mode is perfectly acceptable for JPEG, it's not acceptable on the Web. Your images need to be converted to RGB before they can be seen by a Web browser. Throw away the CMYK JPEGs and go back to the originals. Use Save for Web rather than Export, and the color mode will automatically be converted for you.

What's that? Why does JPEG accept CMYK if you can't see it on the Web? Well, JPEG does more than just Web graphics. It's also one of the major file formats used to compress images for storage or archiving—and many of those images are CMYK.

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