Why NTSC and PAL Still Matter With HDTV

How digital TV and HDTV are linked to analog television standards

Many TV viewers in the U.S. and around the world assume with the introduction and acceptance of Digital TV and HDTV broadcasting and source devices (such as Blu-ray disc players and media streaming), the old barriers to a universal video standard have been removed.

This information applies to TVs from a variety of manufacturers including, but not limited to, those made by LG, Samsung, Panasonic, Sony, and Vizio.

Frame Rate

Despite the fact video is now mostly digital, the frame rate used in analog video systems have been incorporated into Digital TV and HDTV standards.

In a video (Analog, HD, and even 4K Ultra HD), just as in film, the images viewed on a TV or video projection screen look like complete frames. However, there are differences in the way frames are transmitted by broadcasters, transferred via streaming or physical media devices, and/or displayed on a screen.

Lines and Pixels

Video images broadcast live or recorded, are composed of scan lines or pixel rows. Unlike film, where the whole image is displayed at once, the lines or pixel rows in a video image are displayed across a screen starting at the top of the screen and moving to the bottom. Lines or pixel rows can be displayed in two ways.

Interlaced Scan vs Progressive Scan
Interlaced Scan vs Progressive Scan. Samsung
  1. The first way to transmit or display images is to split the lines into two fields. Odd-numbered lines or pixel rows are displayed first and even-numbered lines or pixel rows are displayed next, producing a complete frame. This process is called interlacing or interlaced scan.
  2. The second method is referred to as progressive scan. Instead of transmitting or displaying lines or pixel rows as two alternate fields, they are displayed sequentially. This means both odd and even-numbered lines/pixel rows are displayed in numerical sequence.

The number of vertical lines or pixel rows dictates image detail. The larger the number of vertical lines or pixel rows, the more detail. The number of vertical lines or pixel rows is fixed within a system.

NTSC and PAL

The two main analog video systems are (were) NTSC and PAL.

  • NTSC — a 525-line or pixel row, 60 fields/30 frames-per-second, at 60 Hz system for transmission and display of video images. Each frame is transmitted in two fields of 262 lines or pixel rows that are displayed alternately (interlaced). The two fields are combined so that each frame is displayed with 525 lines or pixel rows. NTSC has been the official analog video standard in the U.S., Canada, Mexico, some parts of Central and South America, Japan, Taiwan, and Korea.
  • PAL — the dominant format in the World for analog TV broadcasting and analog video display. PAL is a 625 line or pixel row, 50 field/25 frames a second, 50Hz system. The signal is interlaced, like NTSC, into two fields, composed of 312 lines or pixel rows each. Since there are fewer frames (25) displayed per second, a slight flicker in the image is sometimes noticeable, like the flicker on projected film. However, PAL has a slightly higher resolution and better color stability than NTSC. Countries with roots in the PAL system include the U.K., Germany, Spain, Portugal, Italy, China, India, Australia, most of Africa and the Middle East.
NTSC PAL SECAM Chart
Wikimedia Commons / Public Domain

DigitalTV/HDTV and NTSC/PAL Frame Rates

Although the increased resolution of digital and high definition broadcast and video software content standards are a step up, when comparing HDTV to analog NTSC/PAL standards, the common foundation of both systems is the Frame Rate.

  • In NTSC-based countries, there are 30 separate frames displayed every second (1 complete frame every 1/30th of a second).
  • In PAL-based countries, there are 25 separate frames displayed every second (1 complete frame displayed every 1/25th of a second).

These frames are either displayed using the interlaced scan method (480i or 1080i) or the Progressive Scan method (480p, 720p or 1080p).

This means that with Digital TV and HDTV, the frame rate still has roots in the original NTSC and PAL analog video formats. In former NTSC-based countries, Digital and HDTV use the 30 Frame-per-second frame rate, while former PAL-based countries use a 25 frame-per-second frame rate.

NTSC-Based Digital TV/HDTV Frame Rate

Where Digital/HDTV evolved from NTSC if frames are transmitted as an interlaced image (1080i), each frame is composed of two fields, each displayed every 60th of a second, and a complete frame displayed every 30th of a second, using an NTSC-based 30 frames-per-second frame rate.

If the frame is transmitted in the progressive scan format (720p or 1080p) it is displayed twice every 30th of a second.

PAL-Based Digital TV/HDTV Frame Rate

Where Digital/HDTV evolved from PAL if frames are transmitted as an interlaced image (1080i), each frame is composed of two fields, each displayed every 50th of a second, and a complete frame displayed every 25th of a second, using a PAL-based 25 frames-per-second frame rate.

If the frame is transmitted in the progressive scan format (720p or 1080p) it is displayed twice every 25th of a second.

The Bottom Line

Digital TV, HDTV, and Ultra HD, although a big leap forward in what you see on a TV or projection screen still has roots in analog video standards that are more than 65 years old.

As a result, there are and will be, for the foreseeable future, differences in Digital and HDTV standards in use throughout the world, reinforcing the barrier to a true worldwide video standard.

Also, as conversion continues towards digital and HD only transmission, many still have NTSC and PAL-based video playback devices, such as VCRs, analog camcorders, and non-HDMI equipped DVD players plugged into HDTVs (and even 4K Ultra HD TVs).

Even with formats, such as Blu-ray Disc, there are cases where the film or main video content may be in HD, but some of the supplementary video features may be in the standard resolution NTSC or PAL formats.

DVDs are still made in either the NTSC or PAL formats.

Although 4K content is now widely available via streaming and Ultra HD Blu-ray Disc, 4K TV broadcast standards are still in the early stages of implementation. TVs that are 4K-compliant still need to support analog video formats as long as there are analog video playback devices in use.

8K resolution streaming and broadcasting may not be that far off.

Eventually, you may no longer be able to use analog video devices, but that day isn't there quite yet.