AA-15 Desktop Color PrimerThe amount of data found in a raster image depends on its resolution and bit depth.The resolution of a raster describes the compactness of the pixels and is specified inpixels per inch (ppi). The bit depth is the number of bits of information assigned toeach pixel. Black and white raster images require only one bit of information per pixel.Grayscale images require 8 bits per pixel. For photographic quality color, 24 bits ofRGB color information are required per pixel, yielding 256 levels of red, green, andblue. For CMYK images, 32 bits per pixel are required.When printing raster artwork, the quality of the output depends on the resolution ofthe source raster. If the raster resolution is too low, individual pixels become visible inthe printed output as small squares. This effect is sometimes called “pixelation.”In vector graphics, picture objects are defined mathematically as lines or curvesbetween points—hence the term “vector” (see example b). Picture elements can havesolid, gradient, or patterned color fills. Vector artwork is created in illustration anddrawing applications, such as Illustrator and CorelDRAW. Page layout applications,such as QuarkXPress, also allow you to create simple vector artwork with their drawingtools. PostScript fonts are vector-based, as well.Vector artwork is resolution-independent; it can be scaled to any size and resolutionwithout danger of pixels becoming visible in printed output.a b
