Interapplication File Formats

In the name of interapplication harmony, Photoshop supports a few software specific formats that permit you to trade files with popular object-oriented programs such as Illustrator and QuarkXPress.

Every one of these formats is a variation on EPS (Encapsulated PostScript), which is based in turn on Adobe’s industry-standard PostScript printing language. You can use Photoshop to edit frames from a QuickTime movie created with Adobe Premiere.

Rasterizing an Illustrator or FreeHand file

Photoshop supports object-oriented files saved in the EPS format. EPS is specifically designed to save object-oriented graphics that you intend to print to a PostScript output device.

Just about every drawing and page-layout program on the planet (and a few on Mars) can save EPS documents. Prior to Version 4, Photoshop could interpret only a small subset of EPS operations supported by Illustrator (including the native .ai format).

But then Photoshop 4 came along and offered a full-blown EPS translation engine, capable of interpreting EPS illustrations created in FreeHand, CorelDraw, Deneba’s Canvas, and more. You can even open EPS drawings that contain imported images, something else Version 3 could not do.

When you open an EPS or native Illustrator document, Photoshop rasterizes (or renders) the artwork—that is, it converts the artwork from a collection of objects to a bitmapped image.

During the open operation, Photoshop presents the Rasterize Generic EPS Format dialog box, which enables you to specify the size and resolution of the image, just as you can in the New dialog box.

Figure-1: You can specify the size and resolution at which Photoshop renders an EPS illustration.

Assuming the illustration contains no imported images, you can render it as large or as small as you want without any loss of image quality. If the EPS illustration does contain an imported image or two, you need to know the resolution of the images and factor this information into the Rasterize Generic EPS Format dialog box.

Select anything but Pixels from both the Width and Height popup menus, and leave the suggested values unchanged. Then enter the setting for the highest-resolution imported image into the Resolution option box. (If all the images are low-res, you may want to double or triple the Resolution value to ensure that the objects render smoothly.)

You should always select the Anti-aliased check box unless you’re rendering a very large image say, 300 ppi or higher. Antialiasing blurs pixels to soften the edges of the objects so they don’t appear jagged.

When you’re rendering a very large image, the difference between image and printer resolution is less noticeable, so antialiasing is unwarranted. Photoshop renders the illustration to a single layer against a transparent background.

Before you can save the rasterized image to a format other than native Photoshop, you must eliminate the transparency by choosing Layer>Flatten Image. Or save a flattened version of the image to a separate file by choosing the As a Copy option in the Save dialog box.

Rendering an EPS illustration is an extremely useful technique for resolving printing problems. If you regularly work in Illustrator or FreeHand, you no doubt have encountered limit check errors, which occur when an illustration is too complex for an imagesetter or other high-end output device to print.

If you’re frustrated with the printer and tired of wasting your evening trying to figure out what’s wrong (sound familiar?), use Photoshop to render the illustration at 300 ppi and print it. Nine times out of ten, this technique works flawlessly.

If Photoshop can’t parse the EPS file—a techy way of saying Photoshop can’t break down the individual objects it attempts to open the PICT (Mac) or TIFF (Windows) preview. This exercise is usually futile, but occasionally you may wish to take a quick look at an illustration to, say, match the placement of elements in an image to those in the drawing.

Placing an EPS Illustration

If you want to introduce an EPS graphic into the foreground image rather than to render it into a new image window of its own, choose File>Place. Unlike other File menu commands, Place supports only EPS illustrations and PDF files.

After you import the EPS graphic, it appears inside a box which Photoshop calls a bounding box>with a great big X across it. You can move, scale, and rotate the illustration into position before rasterizing it to pixels. Drag a corner handle to resize the image; drag outside the image to rotate it.

You can also nudge the graphic into position by pressing the arrow keys. When everything is the way you want it, press Enter or double-click inside the box to rasterize the illustration.

If the placement isn’t perfect, not to worry. The graphic appears on a separate layer, so you can move it with complete freedom. To cancel the Place operation, press Escape instead of Enter.

Saving an EPS Image

When preparing an image for placement inside a drawing or page-layout document that will be printed to a PostScript output device, many artists prefer to save the image in the EPS format. Converting the image to PostScript up front prevents the drawing or page-layout program from doing the work.

The result is an image that prints more quickly and with less chance of problems. (Note that an image does not look any different when saved in EPS. The idea that the EPS format somehow blesses an image with better resolution is pure nonsense.)

A second point in the EPS format’s favor is clipping paths. A clipping path defines a free-form boundary around an image. When you place the image into an object-oriented program, everything outside the clipping path becomes transparent.

While some programs notably InDesign and PageMaker recognize clipping paths saved with a TIFF image, many programs acknowledge a clipping path only when saved in the EPS format.

Third, although Illustrator has remedied the problems it had importing TIFF images, it still likes EPS best, especially where screen display is concerned. Thanks to the EPS file’s fixed preview, Illustrator can display an EPS image on screen very quickly compared with other file formats.

And Illustrator can display an EPS image both in the preview mode and in the super-fast artwork mode. So if you want to import an image into Illustrator, QuarkXPress, or another objectoriented program, your best bet is EPS.

On the downside, EPS is an inefficient format for saving images thanks to the laborious way that it describes pixels. An EPS image may be three to four times larger than the same image saved to the TIFF format with LZW compression.

But this is the price we pay for reliable printing. Absolutely avoid the EPS format if you plan on printing your final pages to a non-PostScript printer. This defeats the entire purpose of EPS, which is meant to avoid printing problems, not cause them. When printing without PostScript, use TIFF or JPEG.

To save an image in the EPS format, choose Photoshop EPS from the Format pop-up menu in the Save dialog box. After you press Enter, Photoshop displays the dialog box shown below.

Figure-2: When you save an image in the EPS format, you can specify the type of preview and tack on some printing attributes.

The options in this dialog box work as follows:

  • Preview: Technically, an EPS document comprises two parts: a pure PostScriptlanguage description of the graphic for the printer and a bitmapped preview so you can see the graphic on screen. Select the TIFF (8 bits/pixel) option from the Preview pop-up menu to save a 256-color TIFF preview of the image.

The 1-bit option provides a black-and-white preview only, which is useful if you want to save a little room on disk. Select None to include no preview and save even more disk space.

  • Encoding: If you’re saving an image for import into Illustrator, QuarkXPress, or some other established program, select the Binary encoding option (also known as Huffman encoding), which compresses an EPS document by substituting shorter codes for frequently used characters.

The letter a, for example, receives the 3-bit code 010, rather than its standard 8-bit ASCII code, 01100001 (the binary equivalent of what we humans call 97). Sadly, some programs and printers don’t recognize Huffman encoding, in which case you must select the less efficient ASCII option.

ASCII stands for American Standard Code for Information Interchange, which is fancy jargon for text-only. In other words, you can open and edit an ASCII EPS document in a word processor, provided you know how to read and write PostScript.

Actually, this can be a useful technique if you have a Mac file that won’t open, especially if the file was sent to you electronically. Chances are that a Macspecific header got into the works. Open the file in a word processor and look at the beginning.

You should see the four characters %!PS. Anything that comes before this line is the Macintosh header. Delete the garbage before %!PS, save the file in text format, and try again to open the file in Photoshop. The remaining Encoding options are JPEG settings.

JPEG compression not only results in smaller files on disk but also degrades the quality of the image. Select JPEG (Maximum Quality) to invoke the least degradation. Better yet, avoid the JPEG settings altogether.

These options work only if you plan to print your final artwork to a PostScript Level 2 or Level 3 device. EarlierPostScript printers do not support EPS artwork with JPEG compression and will choke on the code. So to recap, ASCII results in really big files that work with virtually any printer or application.

Binary creates smaller files that work with most mainstream applications but may choke some older-model printers. And the JPEG settings are compatible exclusively with Level 2 and later PostScript printers.

  • Include Halftone Screen: Another advantage of EPS over other formats is that it can retain printing attributes. If you specified a custom halftone screen using the Screens button inside the Page Setup dialog box, you can save this setting with the EPS document by selecting the Include Halftone Screen check box. But be careful you can just as easily ruin your image as help it.

  • Include Transfer Function: You can change the brightness and contrast of a printed image using the Transfer button inside the Page Setup dialog box. To save these settings with the EPS document, select the Include Transfer Function check box. Again, this option can be dangerous when used casually.

  • PostScript Color Management: Like JPEG compression, this check box is compatible with Level 2 and 3 printers only. It embeds a color profile, which helps the printer to massage the image during the printing cycle to generate more accurate colors. Unless you plan on printing to a Level 2 or later device, leave the option off.

  • Include Vector Data: Select this option if your file contains vector objects, including shapes, non-bitmap type, and layer clipping paths. Otherwise, Photoshop rasterizes the objects during the save process.

When you select the option, Photoshop displays a warning in the dialog box to remind you that if you reopen the file in Photoshop, you rasterize any vector objects that you saved with the file.

  • Transparent Whites: When saving black-and-white EPS images in Photoshop, the four check boxes previously discussed drop away, replaced by Transparent Whites. Select this option to make all white pixels in the image transparent.

Although Photoshop EPS is the only format that offers the Transparent Whites option, many programs including Illustrator and InDesign treat white pixels in black-and-white TIFF images as transparent as well.

  • Image Interpolation: Turn on this option if you want another program to be able to interpolate the image when resampling it to another size. For example, suppose you import an EPS image into InDesign and scale it to 400 percent.

If Image Interpolation is turned off, then InDesign just makes pixels in the image four times larger, as if you had used the nearest neighbor interpolation inside Photoshop.

If you turn Image Interpolation on, however, InDesign applies bicubic interpolation in order to generate new pixels. Unless you have a reason for doing otherwise, turn this option on.

QuarkXPress DCS

Quark developed a variation on the EPS format called Desktop Color Separation (DCS). When you work in QuarkXPress, PageMaker, and other programs that support the format, DCS facilitates the printing of color separations.

Before you can use DCS, you have to convert your image to the CMYK color space using Image>Mode>CMYK Color. (DCS 2.0 also supports grayscale images with spot-color channels.)

Then bring up the Save dialog box and select Photoshop DCS 1.0 or 2.0 from the Format pop-up menu. Photoshop 5 introduced support for DCS 2.0 to accommodate images that contain extra spot-color channels. If you add a Pantone channel to an image, DCS 2.0 is the only PostScript format you can use.

If your image doesn’t contain any extra channels beyond the basic four required for CMYK, DCS 1.0 is the safer and simpler option. After you press Enter, Photoshop displays an additional pop-up menu of DCS options, which vary depending on whether you’ve selected DCS 1.0 or 2.0, as shown below.

Figure-3: The extra options for the DCS 1.0 format (top) and those for the DCS 2.0 format (bottom).

The DCS 1.0 format invariably saves a total of five files: one master document (which is the file that you import into QuarkXPress) plus one file each for the cyan, magenta, yellow, and black color channels (which are the files that get printed).

The DCS 2.0 format can be expressed as a single file (tidier) or five separate files (better compatibility). Either way, the DCS pop-up menu gives you the option of saving a 72-ppi PostScript composite of the image inside the master document.

Independent from the bitmapped preview which you specify as usual by selecting a Preview option the PostScript composite makes it possible to print a low-resolution version of a DCS image to a consumer- quality printer.

If you’re using a black-and-white printer, select the 72 pixel/inch grayscale option; if you’re using a color printer, select the final option. Be forewarned, however, that the composite image significantly increases the size of the master document on disk.

Notice the two new options at the bottom of the options dialog boxes for DCS 1.0 and 2.0: Include Vector Data and Image Interpolation. These options work just as described earlier for the Photoshop EPS format.

Premiere Filmstrip

Adobe Premiere is a popular QuickTime movie-editing application for both Macs and PCs. The program is a wonder when it comes to fades, frame merges, and special effects, but it offers no frame-by-frame editing capabilities.

For example, you can neither draw a mustache on a person in the movie nor can you make brightly colored brush strokes swirl about in the background at least, not inside Premiere.

You can export the movie to the Filmstrip format, though, which is a file-swapping option exclusive to Photoshop and Premiere. A Filmstrip document organizes frames in a long vertical strip, as shown on the left side of Figure-4.

Figure-4: Four frames from a QuickTime movie as they appear in the Filmstrip format before (left) and after (right) editing the frames in Photoshop.

The right side of the figure shows the movie after I edited each individual frame in ways not permitted by Premiere. A boring movie of a cat stuck in a bag becomes an exciting movie of a cat-stuck-in-a-bag flying. If that doesn’t sum up the miracle of digital imaging, I don’t know what does.

A gray bar separates each frame. The number of each frame appears on the right; the Society of Motion Picture and Television Engineers (SMPTE) time code appears on the left. The structure of the three-number time code is minutes:seconds:frames, with 30 frames per second.

If you change the size of a Filmstrip document inside Photoshop in any way, you cannot save the image back to the Filmstrip format. Feel free to paint and apply effects, but stay the heck away from the Image Size and Canvas Size commands.

I don’t really delve into the Filmstrip format anywhere else, so I want to pass along a few quick Filmstrip tips right here and now:

  • First, you can scroll up and down exactly one frame at a time by pressing Shift+Page Up or Shift+Page Down, respectively.

  • Second, you can move a selection exactly one frame up or down by pressing Ctrl+Shift+up arrow or Ctrl+Shift+down arrow.

  • If you want to clone the selection as you move it, press Ctrl+Shift+Alt+up arrow or Ctrl+Shift+Alt+down arrow. And finally here’s the great one you can select several sequential frames and edit them simultaneously by following these steps:

STEPS: Selecting Sequential Frames in a Movie

  1. Select the first frame you want to edit. Select the rectangular marquee tool by pressing the M key. Then drag around the area you want to edit in the movie. (This is the only step that takes any degree of care or coordination whatsoever.)

  2. Switch to the quick mask mode by pressing the Q key. The areas around the selected frame are overlaid with pink.

  3. Set the magic wand Tolerance value to 0. Double-click the magic wand tool icon in the Toolbox to display the Magic Wand Options palette. Enter 0 for the Tolerance value and deselect the Anti-aliased check box.

  4. Click inside the selected frame (the one that’s not pink) with the magic wand tool. This selects the unmasked area inside the frame.

  5. Press Ctrl+Shift+Alt+down arrow to clone the unmasked area to the next frame in the movie. When you exit the quick mask mode, both this frame and the one above it will be selected.

  6. Repeat several times. Keep Ctrl+Shift+Alt+down arrowing until you’re rid of the pink stuff on all the frames you want to select.

  7. Exit the quick mask mode by pressing the Q key again. All frames appear selected.

  8. Edit the frames to your heart’s content.

If you’re new to Photoshop, half of these steps, if not all of them, probably sailed over your head like so many low-flying cats stuck in bags. The process of editing individual frames as just described is sometimes called rotoscoping, named after the traditional technique of combining live-action film with animated sequences.

You also can try out some scratch-and-doodle techniques, which is where an artist scratches and draws directly on frames of film. If this isn’t enough, you can emulate xerography, in which an animator makes Xerox copies of photographs, enhances the copies using markers or whatever else is convenient, and shoots the finished artwork, frame by frame, on film.

In a nutshell, Photoshop extends Premiere’s functionality by adding animation to its standard supply of video-editing capabilities. You can save an image in the Filmstrip format through the Save dialog box. But remember, you can save in this format only if you opened the image as a Filmstrip document and did not change the size of the image.