High-definition television

High-definition television (HDTV) is a way to make TV pictures clearer and sharper than older types of TV. The word started being used in 1933, but today it mostly means the TV system that came after standard-definition television (SDTV).

HDTV is used in most TV broadcasts today. This includes TV watched over the air with antennas, TV from cable services, and TV from satellites. Because of HDTV, TV pictures look much better and more detailed.

Formats

HDTV can be shown in different ways, each with its own size and style. Common formats include 720p and 1080p, which give a clearer picture. Some places also use special sizes like 1440 × 1080i.

HDTV has more pixels than older TV systems, so the picture looks sharper and more detailed. It also uses special ways to show motion, making fast action look better. HDTV started in Japan in 1989 and became popular around the world in the late 2000s.

Standards

All modern high-definition broadcasts use digital television standards.

The main digital television systems used for TV, cable, satellite, and mobile devices include:

• DVB, used in Europe and also in parts of Asia, Africa, and Australia
• ATSC, used in much of North America
• DTMB, used in China and nearby countries
• ISDB, used in two different ways in Japan and South America
• DMB, used for mobile devices in South Korea

These systems use different video codecs, some of which are also used for internet video.

History

The idea of high-definition television started in the 1930s. It meant a TV system with more lines than older ones. Over the years, countries and companies worked to make better TV systems.

In the 1980s and 1990s, new digital technology made high-definition TV possible. Digital HDTV could start in the late 1990s and early 2000s. Later, even better systems like 4K, 5K, and 8K were developed.

The UK began testing HDTV in 1936. France followed in 1938, and the US started in 1941. France made a very high-definition system in 1949, but it was too expensive to use widely. All these early systems used a special way to show images called "interlacing" except for one British system.

Color TV started in the 1950s and 1960s, using the same number of lines as before but adding color.

In the late 1980s, Japan and Europe tried to make analog HDTV systems. But then, a company in the US showed that a digital HDTV system could work. This led to new rules for HDTV, making it digital and much better than old analog TV.

Many companies worked together to create a new digital HDTV system. This system used special technology to compress the video, making it possible to broadcast over the air, by cable, and by satellite.

Since the mid-2000s, old analog TV systems like NTSC, PAL, and SECAM have been seen as standard-definition. HDTV uses digital signals with much higher resolution.

Notation

HDTV broadcast systems are identified by three main features: frame size, scanning system, and frame rate. Frame size tells us the number of pixels in each picture, like 1280 × 720 or 1920 × 1080. The scanning system can be progressive (p) or interlaced (i). Frame rate is how many pictures are shown each second.

When all three features are used, they are written together, like 1920×1080p25, which means progressive scanning with 25 pictures every second, each picture being 1,920 pixels wide and 1,080 pixels tall. Other examples include 1080i25 or 720p60. Different countries use different frame rates, like 50 Hz or 60 Hz.

Most HDTV systems use common resolutions and frame rates, and they show more detail than older TV systems. They also use a 16:9 shape for the screen without stretching or adding black bars. However, sending very high-resolution pictures can need a lot of space, so compression is used.

Recording and compression

Main article: High-definition pre-recorded media and compression

HDTV can be saved onto special tapes like D-VHS or W-VHS, or onto special digital boxes such as DirecTV, Sky HD, Dish Network, or TiVo. Some cable boxes can show or save more than one HDTV show at the same time.

Because HDTV needs a lot of space to save, regular tapes cannot hold it. A device can save HDTV shows onto a computer’s hard drive or DVD. Newer systems can save shows exactly as they are broadcast or change the format to work better with Blu-ray players.

Older analog tapes that could save HDTV are no longer made for regular users and are hard to find. Some set-top boxes can save the digital show directly, including extra information like teletext. However, saving encrypted shows needs special permission. In the United States, cable companies must give customers a box with a special connection called FireWire if asked, but satellite companies do not need to. This saved content is protected to stop copying.