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 it an industry-wide standard, Macromedia opened its Flash file format in April 1998, making it freely available to content and tools developers. This distinction can loom large, for example, when clients or coworkers ask you to alter the text on an image.