VECTOR AND RASTER GRAPHICS

The physical device used with the Sketchpad program to produce graphic images was the cathode ray tube (CRT), an essential element of the television set at that time. In order to produce images on the CRT screen that served as the computer’s monitor, there had to be some way of generating two-dimensional graphics from the computer’s output. The two basic approaches to this are vector and raster graphics. With the former precise geometric data, layout, and style is stored. This includes the coordinate positions of points, the connections between points (to form lines or paths), the color, and the thickness of the shapes. Most vector graphic systems also have a library of standard shapes such as circles and rectangles.
With raster graphics, a grid of picture elements, each with its own color and brightness is projected onto the screen. This grid is composed of a number of horizontal and vertical lines: a standard PC display has 1,024 of the former, 768 of the latter. At the intersection of each horizontal and vertical line is a point known as a pixel (or picture element) and it is the combination of all the pixels on the screen that define the image. It is possible to adjust the image resolution by having more lines (for higher resolution) or fewer (for lower resolution).