Raster graphics system

Figure 5 A CPK-style model displayed on a raster graphics system, circa 1979...

As the graphical capabilities of the computer systems became more powerful simultaneously the number of visualized structures increased. With the introduction of raster graphics (1974) and colored raster graphics displays (1979), other forms of molecular representations were possible [197]. CPK models could be represented and colored bonds or molecular surfaces could be visualized. 

The cathode ray tubes are scanned in a raster like a television picture. Each scan line is modulated into a series of dots called picture elements (abbreviated to pixels or pels) and each character is built up from these pixels. It soon became possible to manipulate the pixels individually so that as well as characters, dots, lines and shapes could be displayed on the screen. Microcomputers are now available with graphics capabilities rivalling those found on mainframe systems, but at a fraction of the cost. Clearly, more memory locations have to be put aside for graphics displays. For example, compare the text (character) display of the IBM Color/Graphics display with its high-resolution monochrome graphics mode. The 80-character mode puts 25 rows of 80 characters on the screen. Each character is stored in two bytes - one for the character itself and one for its attributes , that is, colour. 

---