Abstract

In the broadcast television environment, interlaced scanning is universal, although the advantage it has over the inherently simpler sequential scan is not obvious. By examining the fundamentals of television scanning in frequency-domain terms, it is concluded that the main benefit of interlaced scanning is that it is better matched to the slow roll-off vertical frequency characteristic of the cathode-ray tube with the result that the line structure is less noticeable. With advances in technology, other methods of improving the displayed picture quality can be considered, such as up-conversion in the display to higher line and field rates. However this conversion process would be considerably simpler with a sequential input to the display unit and might more successfully overcome the movement problems of interlaced scanning in which vertical and temporal frequencies are difficult to distinguish. This preference for a sequential input to the display unit brings with it a desirability to broadcast and possibly also to originate the television signals in sequential form. Moreover, in this context, it is considered that sequential scanning may have further advantages, both simplifying down-conversion from a higher scanning rate used in the camera and making low field-rate, movement compensated bandwidth compression techniques more effective. It is concluded, therefore, that sequential scanning may have an important part to play in the development of future television systems.