Images Life would have been so much simpler if computers had just stuck to the business of text and numbers. But almost from the get-go, everybody wanted computers to tackle more. While science fiction writers imagined computers eventually playing music and movies, computer pioneers had the more modest goal of getting machines to handle pictures.
They wanted this, of course, because they knew that humans are far better with images than with words. So they came up with rudimentary graphics displays for missile defense work way back in the early 1950s. And, of course, the Xerox PARC and Apple innovations in the late 1970s and early 1980s showed the power of using graphics to control computers.
But almost at the same time, inventors saw how cool it would be to use computers to control graphics. Early graphics programmers quickly realized that they could get at images in two primary ways. They could build the images up bit by bit or describe them using funky math formulae with weird names like bezier curves and splines.
Raster Graphics The bit-by-bit option is called a raster image. "Raster," which was once a synonym for "barber," shares the same origins as the word "razor." Basically, it means "to scrape"-which is what an electron beam does to the front of the cathode ray tube that is the business end of a computer monitor as it builds up a picture for you to see. The analogy was quickly transferred to any image that is made up of the small dots called pixels. Photographs are almost always stored as raster images.
Unfortunately, each dot has to be told what color to be, what range of colors it can hold and where exactly to appear (which is why raster graphics are sometimes called bitmaps). Consequently, the resulting files can get plenty big. And after you have told all the dots what to do, it's a tough job to get them to do anything else-like be a different size. Once a raster image's width and height in pixels is set, it can't readily be made smaller or larger without introducing "artifacts" such as jaggy lines and blockiness.
Vector Graphics Now, not every image is a photograph. Line drawings and true graphics are much simpler. Think of a cartoon. Why should you have to tell every pixel what to do when most of the image space is blank or a solid color? Well, you don't. All you need is a lot of math to describe the vectors and objects (lines, polygons and colors) that make up the image. With enough fancy arithmetic, you can get some remarkably realistic-looking images.
Because a vector graphic file stores only a mathematical abstract of the image and not every tiresome detail, you end up with much smaller file sizes and the ability to scale images up or down with little quality loss. This combination of small file size and scalability has made vector graphics the preferred choice for Web-based imagery. Macromedia's Flash and Adobe Acrobat are vector graphics programs. On your desktop, TrueType and PostScript fonts are good examples of the power of vector graphics.
BMP Whether raster or vector, an image needs to be stored in a way that lets the computer know that it's an image file instead of, say, a spreadsheet or text file. To that end, there are now dozens of image file formats. BMP is Microsoft's version of bitmapping and was designed for displaying images in the Windows environment. It worked great on old VGA monitors with limited color-handling capability-but the higher the resolution of the bitmapped image, the less efficient this format is. Best use: Screen savers on Wintel machines. Downside: Poor compression and isn't very good at handling photographs or managing print output.
GIF As an early alternative to the BMP format, CompuServe developed the Graphic Interchange Format. Designed in a simpler time, it can only handle up to 256 colors. Best use: Limited color resolution makes a GIF file inherently small, which is great for the Web. Because it can be compressed to a tiny size (albeit at the cost of image data loss) and be displayed quickly on Web pages, GIF is a dominant image format on the Internet. Downside: Not a format for high-quality photographs, especially if you intend to print them.
TIFF For that, you need something like the Tagged Image File Format, which can handle a much greater range of colors and shades. Aldus (now part of Adobe) concocted TIFF in the late '80s to work with scanned images-which made the format popular for faxes. Best use: Can be played on almost any type of computer and supports a "lossless" compression scheme that crunches and de-crunches photos without quality degradation. It's the best format for archiving your prized digital photos. Downside: TIFF files are huge.
JPEG Big fat TIFF files are a drag to e-mail to your mom. A 9MB TIFF file would choke a goat. The Joint Photographers Expert Group understood this and came up with the JPEG format, which allows digital images to be compressed in all kinds of clever ways. Of course, the more you compress a JPEG file, the more information you lose, but a lot of what's lost isn't very noticeable (even when the compression ratio is as high as 25:1), so big deal. Best use: You can play with a photo file's size so that it can be more easily handled and transferred. Downside: Every time you save an image as a JPEG file, you irretrievably lose information. The more often you do this, the more damage gets done. You'll want to save your best pics directly from your camera into a TIFF file, burn them to a CD and then convert copies of the source TIFF into JPEG files for manipulation and transfer. And you thought digital photography was a breeze.
Mark Tamminga ( firstname.lastname@example.org) practices law and fiddles with software at Gowling Lafleur Henderson LLP in Toronto. He is the coauthor of the new ABA book The Lawyer's Guide to Extranets.