Raster vs. vector

by Guest Contributor | Sep 29, 2003 7:33:00 PM

Takeaway: When you start working directly with image files, how the image data is recorded determines your options for changing it. Learn the difference between raster and vector images files.

By Paul Anderson

No, it's not some ancient Greek family tragedy. When you start working directly with image files, how the image data is recorded determines your options for changing it.

On a computer monitor, images are nothing more than variously colored pixels. Certain kinds of image-file formats record images literally in terms of the pixels to display. These are raster images, and you can edit them only by altering the pixels directly with a bitmap editor. Photoshop and Paint Shop Pro are two of the most popular bitmap editors.

Vector image files record images descriptively, in terms of geometric shapes. These shapes are converted to bitmaps for display on the monitor. Vector images are easier to modify, because the components can be moved, resized, rotated, or deleted independently. PostScript is a popular vector format for printing, but so far Macromedia's Flash is the closest thing to a standard vector format on the Web. In an attempt to make Flash an industry-wide standard, Macromedia opened its Flash file format in April 1998, making it freely available to content and tools developers. The W3C has produced an XML-based format called Scalable Vector Graphics (SVG), but browsers have yet to widely support it.

This distinction can loom large, for example, when clients or coworkers ask you to alter the text on an image. Chances are the image is stored in a raster formatted image file, so the change won't be as easy as they think. You'll have to alter the wording by changing the individual pixels themselves. Keep this in mind when creating images that you might have to modify later. Modern graphics tools let you export a raster version of your image for the Web but also save it in a more componentized proprietary format for later editing.

Paul Anderson is associate technical editor for CNET Builder.com. His responsibilities don't include handling graphics, so naturally, he handles them all the time.

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