The system displays 625 scanned lines. The image is scanned from left to right and from top to bottom. Two half-image scans are required to produce a complete image, one for odd lines, and the other for even lines. This type of scan is referred to as interlaced and denoted with “i” interlaced. Half frame scanning time is 1/50th of a second, and it takes 1/25th of a second to produce a complete frame.
The value is not random, and is determined by the mains frequency used in Europe (50 Hz). However, the number of displayed lines is not 625, but 576. Thus, in technical literature, the system is sometimes denoted as ‘576i’. NTSC displays only 480 lines.
The signal can be transmitted via Composite Video, RCA or S-VIDEO connectors.
Fig. 1. Differences in NTSC, PAL and common HD systems resolutions.
“x576” refers to the number of displayed lines.
Comparison of NTSC and PAL systems shows that PAL resolution is ~20% higher than its US counterpart. However, the higher refresh rate makes the NTSC images smoother.
Detailed parameters of the standard can be found in the article: