Special Purpose File Formats

With 20 file formats to choose from, you can imagine that most are not the kinds you’ll be using on a regular basis. In fact, apart from the native Photoshop format, you’ll probably want to stick with TIFF, JPEG, and GIF for Web images and EPS when preparing images for placement into QuarkXPress, PageMaker, and others.

Many of the other formats are provided simply so you can open an image created on another platform, saved from some antiquated paint program, or downloaded from the Web. In the spirit of sweeping away the chaff so we can move on to the good stuff, I cover these special-purpose formats first.

Notice that I lump Web standards GIF and PNG in with the special-purpose formats. The reason is simple if you don’t design for the Web, you rarely need them. On the other hand, if you do design for the Web, the formats take on special significance.

Microsoft Paint’s BMP

BMP (Windows Bitmap) is the native format for Microsoft Paint (included with Windows) and is supported by a variety of Windows and DOS applications. Photoshop supports BMP images with up to 16 million colors. You also can use RLE (Run-Length Encoding), a lossless compression scheme specifically applicable to the BMP format.

The term lossless refers to compression schemes that conserve space on disk without sacrificing any data in the image, such as BMP’s RLE and TIFF’s LZW (Lempel-Ziv-Welch).

The only reasons not to use lossless compression are that it slows down the open and save operations and it may prevent less-sophisticated applications from opening an image. (Lossy compression routines, such as JPEG, sacrifice a user-defined amount of data to conserve even more disk space.)

The most common use for BMP is to create images for use in help files and Windows wallpaper. In fact, rolling your own wallpaper is a fun way to show off your Photoshop skills. For the best results, make sure you set your image to exactly the same pixel dimensions as your screen (which you can check from the Settings panel in the Display control panel).

To conserve memory, you may want to reduce the number of colors in your wallpaper image to 256 using Image>Mode>Indexed Color. When you save the wallpaper image, Photoshop displays the options.

Figure-1: Select the options shown here when saving a BMP image for use as a desktop background. Leave the Depth setting alone.

Generally, you’ll want to select the Windows and Compress (RLE) options, but it really doesn’t matter when creating wallpaper. Don’t mess with the Depth options. Either you reduced the bit depth using the Indexed Color command. There’s no sense in changing the colors during the save process.

To load the wallpaper onto your desktop, right-click anywhere on the desktop and choose the Properties command. This brings up the Display Properties dialog box shown in Figure-2.

Figure-2: You can load a BMP file as desktop wallpaper using the Display Properties control panel provided with Windows 95 and later.

Click the Browse button and locate your BMP image on disk. Then click the apply button to see how it looks.

CompuServe’s GIF

In the old days, the CompuServe online service championed GIF (short for Graphics Interchange Format) as a means of compressing files so you could quickly transfer photographs over your modem. Like TIFF, GIF uses LZW compression, but unlike TIFF, GIF is limited to just 256 colors.

With the advent of the World Wide Web, the GIF format has grown slightly more sophisticated. Two varieties of GIF currently exist, known by the helpful codes 87a and 89a. GIF87a supports strictly opaque pixels; GIF89a permits some pixels to be transparent.

To open either kind of image, choose File>Open. You can save an image with or without transparency by choosing File>Save and selecting CompuServe GIF from the Format pop-up menu.

When you index (reduce) the image to 256 colors which you can do either before or during the file save process select the Transparency check box in the Indexed Color dialog box if you want any areas of the image that are transparent to remain transparent when you view the image file in a Web browser.

If you’re resistant to change and want to create GIFs with transparency via the old Export>GIF89A command, you can; Adobe includes the command as an optional plug-in on the program CD just for old fogeys like you. But you’ll save yourself time and trouble if you get acquainted with the new method: PC Paintbrush’s PCX PCX doesn’t stand for anything.

Rather, it’s the extension PC Paintbrush assigns to images saved in its native file format. Although the format is losing favor, many PCX images are still in use today, largely because PC Paintbrush is the oldest painting program for DOS. Photoshop supports PCX images with up to 16 million colors.

You can find an enormous amount of art, usually clip art, in this format. However, don’t save files to PCX unless a client specifically demands it. Other formats are better. Adobe’s paperless PDF The Portable Document Format (PDF) is a variation on the PostScript printing language that enables you to view electronically produced documents on screen.

This means you can create a publication in QuarkXPress or PageMaker, export it to PDF, and distribute it without worrying about color separations, binding, and other printing costs. Using a program called Adobe Acrobat, you can open PDF documents, zoom in and out of them, and follow hypertext links by clicking highlighted words.

Adobe distributes Mac, Windows, and UNIX versions of the Acrobat Reader for free, so almost anyone with a computer can view your stuff in full, natural color. PDF files come in two flavors: those that contain just a single image and those that contain multiple pages and images.

Photoshop can save only single-image PDF files, but it can open multipage files. The program rasterizes both types of files when it opens them. You open PDF files in different ways depending on what elements of the file you want to access:

  • Use File>Open to open a particular page in a multipage PDF file. After selecting the page you want to view, you can set the image size and resolution of the rasterized file. You also can choose File>Place to add a page as a new layer to an open image; in this case, you can’t control size and resolution before adding the page. However, you can scale the page after the fact as you can any layer.

  • Select Import>PDF Image to bring up a dialog box that enables you to open a particular image in the PDF file.

  • Choose Automate>Multi-Page PDF to PSD to turn each page in the PDF file into a separate Photoshop image file.

The real question, however, is why would you want to open or place a PDF file in Photoshop instead of viewing it in Acrobat, which provides you with a full range of document viewing tools not found in Photoshop? Furthermore, because you can save only single-page PDF files, why on earth would you save to PDF in Photoshop?

I can think of two scenarios where Photoshop’s PDF functions may come in handy:

  • You want to see how images in a PDF document will look when printed on a high-resolution printer. Open the PDF file using File>Open, set the resolution to match that of the output device, and eyeball those images on-screen.

This “soft-proofing” technique enables you to spot defects that may not be noticeable in draft proofs that you output on a low-res printer.

  • You need a convenient way to distribute images for approval or input. You can save an image as a PDF file and send it to clients and colleagues, who can view the image in Acrobat if they don’t have Photoshop.

In Photoshop, you can even add text or voice annotations to your PDF file. In addition to annotations, Photoshop PDF supports layers, transparency, embedded color profiles, spot colors, duotones, and more.

This enables you to route an image for approval without having to flatten the image or otherwise strip it of its Photoshop 6 features. Of course, features not supported by Acrobat aren’t accessible to the viewer.

When you save to PDF in Photoshop, you have a choice of two encoding options. Choose ZIP only for images that feature large expanses of a single color; otherwise, opt for JPEG.

Keep the Quality option set to Maximum to maintain the best print quality, just as you do for regular JPEG files. Select the Include Vector Data and Embed Fonts check boxes to retain any vector graphics and font data, respectively.

Alternatively, you can select the Use Outlines for Text to save text as character outlines that are editable in the PDF file. The final option, Image Interpolation, enables other programs to interpolate the image when resampling to another size.

If you select JPEG encoding, you need a PostScript Level 2 or later printer to output your PDF file. Also be aware that separating files into individual plates can be problematic.

Apple’s PICT

PICT (Macintosh Picture) is the Macintosh system software’s native graphics format. Based on the QuickDraw display language that the system software uses to convey images on screen, PICT handles object-oriented artwork and bitmapped images with equal aplomb.

It supports images in any bit depth, size, or resolution. PICT even supports 32-bit images, so you can save a fourth masking channel when working in the RGB mode. PICT is obviously popular with the Macintosh crowd, especially folks who don’t know much about graphics.

So if you share a lot of files with Mac-type people, you may occasionally be asked to supply images in the PICT format. If you’re trying to save an image in a format that your mom can open on her Mac, for example, PICT may be a better choice than JPEG.

Heck, you can open PICT files inside a word processor, including everything from SimpleText to Microsoft Word. Just be sure mom has QuickTime loaded on her machine. When you save a PICT image, Photoshop lets you set the bit depth.

You should always stick with the default option, which is the highest setting available for the particular image. Don’t mess around with these options; they apply automatic pattern dithering, which is a bad thing.

On the flip side, you may need to open a PICT file a Mac friend sends you. Photoshop can do this, but one problem may trip you up: On the Mac, you have the option of saving PICT files with a variety of JPEG compressions supplied by Apple’s QuickTime.

Unless you have QuickTime installed on your PC—which you might if you do a lot of surfing on the Web you won’t be able to open compressed PICT images.

Pixar Workstations

Pixar has created some of the most memorable computer-animated movies and commercials in recent memory. Examples include the desk lamps playing with a beach ball from Luxo, Jr., the run-amok toddler from the Oscar winning Tin Toy, and the commercial adventures of a Listerine bottle that boxes gingivitis one day and swings Tarzan like through a spearmint forest the next.

But Pixar really made the grade with the feature-length Toy Story, which provided Disney with enough merchandising options to last a lifetime. Pixar works its 3D magic using mondo-expensive workstations.

Photoshop enables you to open a still image created on a Pixar machine or to save an image to the Pixar format so you can integrate it into a 3D rendering. The Pixar format supports grayscale and RGB images.

PNG For The Web

Pronounced ping, the PNG format enables you to save 16 million color images without compression for use on the Web. As I write this, neither Netscape Navigator nor Microsoft Internet Explorer support PNG without the help of a special plug-in.

But for those folks who want full-color images without the pesky visual compression artifacts you get with JPEG, PNG may well be a big player in the future. PNG was invented for the Web and I’ve never seen anyone use it for a purpose other than the Web.

Scitex Image-Processors

Some high-end commercial printers use Scitex printing devices to generate color separations of images and other documents. Photoshop can open images digitized with Scitex scanners and save the edited images to the Scitex CT (Continuous Tone) format.

Because you need special hardware to transfer images from the PC to a Scitex drive, you’ll probably want to consult with your local Scitex service bureau technician before saving to the CT format.

The technician may prefer that you submit images in the native Photoshop, TIFF, or JPEG format. The Scitex CT format supports grayscale, RGB, and CMYK images.

TrueVision’s TGA

TrueVision’s Targa and NuVista video boards enable you to overlay computer graphics and animation onto live video. The effect is called chroma keying because, typically, a key color is set aside to let the live video show through.

TrueVision designed the TGA (Targa) format to support 32-bit images that include 8-bit alpha channels capable of displaying the live video. Support for TGA is widely implemented among professional-level color and video applications on the PC.