Page:Gametronics Proceedings.djvu/132

 The definition and resolution of video "objects" synthesized for game use is limited by the bandwidth and speed of the circuit technology employed. On the receiver end most home TV sets of high quality have a video bandwidth of 4.2 MHz though the average set is more likely to display an effective BW of much less. The perfectly adjusted set will deliver about 340 usable dots per line, but there are qualifications.

The TV picture can be thought of as a rectangular matrix of elements. There are 525 horizontal rows in the NTSC system, each row containing N picture elements called pixels. N can be thought of as a resolution variable set by the speed of the generating system. The complete array forms 1 TV frame, itself defined by 2 fields (shown as dot and dash in the diagram below). Motion is achieved by presenting 30 frames per second, such that persistence of vision comes into play.

Lines are numbered in actual scan order. Each field represents every other actual scan line, with alternate sets of lines interlacing together to form a smooth blend of lines and reduce flicker, since the field rate is twice the frame rate–you see twice as many, "half picture" per time interval.

Notice the ½ line length at top and bottom of frame, which is the interlace match point. Since 525/2 = 262½ each field will have 262½ lines. Some 20 of these lines are actually blanked and do not figure into the picture display time, which will be a maximum of 241 per field.

The video generator must also supply a sync signal to form the basic raster. Sync consists of horizontal pulses, equalization pulses, and serrated vertical pulses. The vertical sync interval is shown in figure 1-A for both fields of an interlaced system. Notice the H/2 period during vertical timing, which is the result of interlace. This maintains H sync during the vertical sync period which is 3H in duration.