Combined Line and Dot Interlace in Television Rasters

A combination of high-order line and dot interlace can be used to reduce the repetition frequency of a TV picture without materially altering the line and field frequencies. The benefit of reduced repetition frequency is an increase in the number of picture elements that can be transmitted in a specified bandwidth. Combined interlace is therefore a possible method for increasing the resolution of an existing TV system, provided some break-up of moving pictures can be tolerated. For Ith-order line interlace and Jth-order dot interlace, the picture period is IJ field periods and the number of picture elements is increased by the factor ½IJ over a normal 2:1 line-interlaced system. The total number of dot sequence patterns in which the raster can be scanned is IJ². A general method is given for calculating these sequences, and the subjective effects of all sequences for I and J up to 7 are cataloged. About half the sequences are degenerate in that they belong to a lower order. The majority of the remainder are subjectively unacceptable because of flicker, line crawl, and snow-storm effects in the CRT display. A few good sequences do exist, however, and if the CRT has a long-persistence phosphor the product IJ can be at least as large as 40. It is therefore possible to transmit medium-resolution graphics (∼10⁶ picture elements) in real time over a 1-MHz channel.

Print ISSN

0361-4573

Published

1974-09

Content type

Original Research

DOI

10.5594/J06922