Vector and Raster Graphics
Photoshop Elements creates and edits two types of graphics that are standard for Web de-sign—raster and vector. A raster image is composed of pixels organized on a grid. Each pixel in a raster image is stored as a particular combination of colors when it is saved. If the size of a raster image is increased, the image editing program adds pixels in a process called interpo-lation. Interpolation lowers the image quality, making raster images resolution dependent. Raster graphics are ideal for images that have subtle gradations of colors such as photographs and original artwork, or images created with the raster tool set in Photoshop Elements. Raster tools are discussed in the next section.
A vector graphic is not stored as a grid of pixels. Instead, a vector graphic is created by a set of user-determined mathematical properties called vectors. These properties include a graphic’s dimensions, attributes and position. Examples of vector graphics in Photoshop Elements are text created with the type tool and shapes created with the shape tool. The shape tool can create rectangles, ellipses, polygons, lines and custom shapes. Vector images exist as individual objects that can be edited separately from one another. They can also be resized without losing clarity because vector information is stored as sets of instruc-tions instead of groups of pixels. It is this characteristic which makes vector graphics res-olution independent. Vector graphics are ideal for creating solid areas of color and text; however, they cannot handle the image quality of photographs or other color-complex images. Figure 3.13 demonstrates the difference between scaling raster and vector graphics. The raster image becomes pixelated while the vector does not lose any clarity.
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