Graphic design software can be used to manipulate images quickly and easily, eliminating the labor of erasing and redrawing. The sign maker can achieve changes of scale, color, and typeface by the simple selection of software menu options. He can store images for future use or recombination. Cutting these computer-composed images into pressure sensitive vinyl film is the basic transferal technology now used by sign makers.   Computers can receive graphic information through an optical scanner, which converts an object on paper into a digital format composed of a mosaic of small square dots. A designer can manipulate this mosaic, called a "bitmap image," in a paint program or bitmap editor. As a bitmap, the object is not defined by a smooth linear outline but rather a volume of small divisible points, with jagged edges. Vinyl cutting plotters are controlled by instructions that define objects by the mathematics of lines and curves, so bitmaps must be converted into the language of vectors before they can be cut. Tracing software performs this translation, following the contours of bitmap images and redefining the object as lines and curves. Vector drawing programs can then manipulate this vector format. Those specific to the sign industry have the ability to control cutting plotters.   Pressure sensitive vinyl film is manufactured in rolls of various widths and colors. The thin film adheres to a carrier paper, so the adhesive is protected until the paper is peeled away. This two layer composite of vinyl and paper is fed into a computer-driven cutting plotter. The knife blade or stylus of the plotter is adjusted to cut through the vinyl but not the carrier paper. Software translates images composed on the computer into instructions that control the x and y movements of the plotter. The plotter responds by cutting the image outline into the vinyl film. Once cut, the sign maker removes the vinyl with its carrier paper from the plotter and then separates the waste areas of vinyl in a process called "weeding."  He or she then covers the weeded design with a sticky paper called "transfer tape," which, when pulled up, will take the vinyl away from its underlying carrier sheet. After placing the taped design onto a surface, he rubs it down to activate the vinyl's adhesive and carefully pulls the tape off, leaving the vinyl design stuck in place. Outdoor life span for pressure sensitive vinyl ranges from three to eight years.    The power of graphic design software makes the manipulation of images easy and vinyl cutting technology allows the perfect reproduction of these images. Nonetheless, the skills required to achieve good design are still the domain of the designer's talent.