Why NTSC and PAL Still Matter With HDTV

How Digital TV and HDTV Are Linked to Analog Television Standards

Man Watching Analog TVs
Man Watching Analog TVs. Getty Images - xavierarnau - Collection: E+

Many TV viewers around the world assume that with the introduction and acceptance of Digital TV and HDTV, the old barriers to a universal video standard have been removed. However, this is a misguided assumption. Despite the fact that video is now mostly digital, the fundamental difference between video standards that existed under analog systems, frame rate, is still the foundation of Digital TV and HDTV standards.

What Frame Rate Is

In a video (both Analog, HD, and even 4K Ultra HD), just as in a film, the images you see on a TV or video projection screen are displayed as frames. However, although what you see is a complete image, there are differences in the way the frames are transmitted by broadcasters, transferred via streaming or physical media, and/or displayed on a television screen.

Lines and Pixels

Video images that are either broadcast live or recorded, are actually made composed of scan lines or pixel rows. However, unlike film, in which the whole image is projected on a screen 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. These lines or pixel rows can be displayed in two ways.

The first way to display images is to split the lines into two fields in which all of the odd numbered lines or pixel rows are displayed first and then all of the even numbered lines or pixel rows are displayed next, in essence, producing a complete frame.

This process is called interlacing or interlaced scan.

The second method of displaying images, which is used in LCD, Plasma, DLP, OLED flat panel TVs and computer monitors, is referred to as progressive scan. What this means is that instead of displaying the lines in two alternate fields, progressive scan allows the lines or pixel rows to be displayed sequentially.

This means that both the odd and even numbered lines or pixel rows are displayed in numerical sequence.

NTSC and PAL

The number of vertical lines or pixel rows dictates the capability to produce a detailed image, but there is more to the story. It is obvious at this point that the larger the number of vertical lines or pixel rows, the more detailed the image. However, within the arena of analog video, the number of vertical lines or pixel rows is fixed within a system. The two main analog video systems are NTSC and PAL.

NTSC is based on a 525-line or pixel row, 60 fields/30 frames-per-second, at 60Hz system for transmission and display of video images. This is an interlaced system in which each frame is displayed in two fields of 262 lines or pixel rows that are displayed alternately. The two fields are combined so that each frame of video is displayed with 525 lines or pixel rows. NTSC was designated as the official analog video standard in the U.S., Canada, Mexico, some parts of Central and South America, Japan, Taiwan, and Korea.

PAL was designated as the dominant format in the World for analog television broadcasting and analog video display. PAL based on 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, sometimes you can notice a slight flicker in the image, much like the flicker seen on projected film. However, PAL offers a higher resolution image 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.

For more background information on the PAL and NTSC analog video systems, including what the PAL and NTSC acronyms actually stand for, check out our companion article: An Overview of Worldwide Video Standards.

DigitalTV/HDTV and NTSC/PAL Frame Rates

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

In terms of traditional video content, in NTSC-based countries there are 30 separate frames displayed every second (1 complete frame every 1/30th of a second), while 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 (represented by 480i or 1080i) or the Progressive Scan method (represented by 720p or 1080p).

With the implementation of the Digital TV and HDTV, the foundation of how frames are displayed still has its roots in the original NTSC and PAL analog video formats. In soon-to-be former NTSC-based countries, Digital and HDTV are implementing the 30 Frame-per-second frame rate, while soon-to-be PAL-based countries are implementing a 25 Frame-per-second Frame rate.

NTSC-based Digital TV/HDTV Frame Rate

Using NTSC as a foundation for Digital TV or HDTV, if the frames are transmitted as an interlaced image (1080i), each frame is composed of two fields, with each field displayed every 60th of a second, and a complete frame displayed every 30th of a second, using an NTSC-based 30 frame-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.

In both cases, a unique high definition frame is displayed every 30th of a second in former NTSC-based countries.

PAL-based Digital TV/HDTV Frame Rate

Using PAL as a foundation for Digital TV or HDTV, if the frames are transmitted as an interlaced image (1080i), each frame is composed of two fields, with each field displayed every 50th of a second, and a complete frame displayed every 25th of a second, using a PAL-based 25 frame-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. In both cases, a unique high definition frame is displayed every 25th of a second on TVs in former PAL-based countries.

For a more in-depth look at Video Frame Rate, as well as Refresh Rate, which is an additional function performed by a TV that also affects how the image looks on the screen, check out our companion article: Video Frame Rate vs Screen Refresh Rate.

The Bottom Line

Digital TV, HDTV, and Ultra HD,  although a big leap forward in terms of what you actually see on a TV or projection screen, especially in terms of increased resolution and detail, still has roots in analog video standards that are more than 60 years old. As a result, there are and will be, for the foreseeable future, differences in Digital TV and HDTV standards in use throughout the world, which reinforces the barrier to true worldwide video standards for both the professional and the consumer.

Also, let us not forget that despite the fact that analog NTSC and PAL TV broadcasts have, or are, being discontinued in a growing number of countries as conversion continues towards digital and HDTV only transmission, there are still many NTSC and PAL-based video playback devices, such as VCRs, analog camcorders, and non-HDMI equipped DVD players still in use around the world that are plugged into and viewed on HDTVs.

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

It is also important that 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, video display devices (TVs) that are 4K-compliant still need to support analog video formats as long as there are analog video transmission and playback devices in use. Also, be warned 8K streaming and broadcasting may not be that far off.

Although the day will come (probably sooner than later), where you may no longer be able to use analog video devices, such as VCRs, the adoption of a truly universal video standard isn't there quite yet.

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