Why NTSC and PAL Still Matter With HDTV

Even 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 not been removed. This article explains why the NTSC and PAL standards still matter.

Frame Rate

Although video is now mostly digital, the frame rate used in analog video systems is incorporated into digital TV and HDTV standards. In video (analog, HD, and 4K Ultra HD), as in film, the images viewed on the screen look like complete frames. However, there are differences in the way frames are transmitted by broadcasters, transferred through streaming or physical media devices, and displayed on a screen.

Lines and Pixels

Video images that are broadcast live or recorded are composed of scan lines or pixel rows. In film, the whole image displays at once. In contrast, the lines or pixel rows in a video image display across the screen, starting at the top of the screen and moving to the bottom. These rows display in either an interlaced or progressive format.

Interlacing or interlaced scan splits the lines into two fields. Odd-numbered lines or pixel rows display first, and even-numbered lines or pixel rows display next, producing a complete frame.

Progressive scan displays rows sequentially instead of transmitting rows as two alternate fields. This means both odd and even-numbered lines or pixel rows display in numerical sequence.

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

NTSC and PAL

The two main analog video systems are NTSC and PAL.

NTSC is a 525-line or pixel row, 60 fields with 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 display alternately (interlaced). The two fields are combined, so each frame displays with 525 lines or pixel rows. NTSC is the official analog video standard in the U.S., Canada, Mexico, some parts of Central and South America, Japan, Taiwan, and Korea.

PAL is the dominant format in the world for analog TV broadcasting and analog video display. It's a 625 line or pixel row, 50 fields with 25 frames a second, 50Hz system. Like NTSC, the signal is interlaced into two fields, composed of 312 lines or pixel rows each. Since fewer frames (25) display 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.

DigitalTV/HDTV and NTSC/PAL Frame Rates

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

In NTSC-based countries, 30 separate frames display every second (one complete frame every 1/30th of a second). In PAL-based countries, 25 separate frames display every second (one complete frame displays every 1/25th of a second). These frames display using either the interlaced scan method (480i or 1080i) or the progressive scan method (480p, 720p, or 1080p).

Where digital and HDTV evolved from NTSC is if frames transmit as an interlaced image (1080i), each frame is composed of two fields, each displays every 60th of a second, and a complete frame displays 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 displays twice every 30th of a second.

PAL-Based Digital TV and HDTV Frame Rate

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

If the frame transmits in the progressive scan format (720p or 1080p), it displays 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 differences in digital and HDTV standards in use throughout the world, reinforcing the barrier to a 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 4K Ultra HD TVs).

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

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

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