What is HD?

Danny Rawles
HD logo

HD stands for High Definition and in TV technology refers to the resolution or number of pixels a TV can display.

HD resolution is between 1280x720 and 1920x1080 pixels in a widescreen (16:9) format.

High resolution displays have actually been around for a long time, longer than you might think.

If you've used a computer monitor in the last 15 years or so you will have already experienced a higher resolution than standard definition TV. This is the principle of what HD is.

What is a Pixel?

To fully understand what HD is and what resolution means, you first need to understand what a pixel is.

Pixels are the tiny individual squares that make up a picture. Higher resolutions mean more pixels which in turn means more detail and higher quality.

Low resolution

A low resolution picture of Michael Jackson from the Bad album
This image has a resolution of 58x58 pixels

High resolution

A high resolution picture of Michael Jackson from the Bad album
This image has a resolution of 290x290 pixels

Although these pictures of Michael Jackson are the same physical size they have very different resolutions.

You can see the individual pixels (squares) that make up the low resolution image. The high resolution image has 5 times more pixels packed into the same area, which makes the picture look clear and sharp.

TV Resolutions

In the UK, a standard definition digital TV has a resolution of 704x576 (width x height).

That's 704 horizontal pixels multiplied by 576 vertical pixels, giving a total pixel count of 405,504 pixels or 0.4 megapixels (mega simply means million).

HD resolution vs. SD resolution

HD resolution

Almost all HDTVs today have a resolution of 1920x1080. That's 2,073,600 pixels or 2.1 megapixels.

Clearly HD wins the pixel count with just over 5 times the amount of pixels or put another way, 5 times the amount of detail.

It's this increase in picture resolution in a widescreen format that defines what it means to be High Definition.

HD Ready vs. Full HD

HDTV logo

The term HD was invented mainly for the TV market and refers to either 720p (1280x720) which was branded HD Ready or the more commonly known 1080p (1920x1080) which was branded Full HD.

HD Ready was introduced first and was the cheaper of the two but these days almost all new HDTVs are Full HD or 1080p.

When looking for a new TV make sure it is Full HD as the price difference is almost negligible now and Full HD will always offer the best overall picture quality.

What's the difference between HD and SD?

About 1.6 million pixels!

Watching standard definition TV or DVDs on an HDTV can be a compromise. The problem is, how do you fit a 0.4 megapixel video into a 2.1 megapixel TV without it looking like the low resolution picture of Michael Jackson above?


This is where a complex processing system called scaling comes in. The original SD image needs to be upscaled to fill the larger resolution.

Upscaling is basically very clever guesswork which attempts to fill in detail that doesn't exist.

This is why SD programmes on an HDTV can look a bit soft and slightly blurry. The better the scaling technology the less you will notice a difference but the simple fact is an upscaled video will never look as good as a true HD video.

An upscaled image of a beetle
An upscaled SD picture
An HD image of a beetle
A native HD picture

Native HD content

Of course where HD really shines is with native HD content. This means any video that was produced at a resolution of 1080p or higher.

No scaling is required and videos don't need to be overly processed giving them a highly detailed, clean, crisp look.

Just beware that even though you might be watching an HD channel on your HDTV doesn't always mean the programme itself will be a native HD programme! Channels still sometimes broadcast SD programmes on HD channels.

Where can you get native HD content?

If you want to experience HD there are a number of ways to achieve this (of course you need an HDTV as a minimum):


  • Freeview HD currently broadcasts 13 HD channels
  • Virgin Media's top TV package comes with 53 HD channels
  • Sky's top TV package if you choose absolutely everything has 75 HD channels

Blu-ray & Online streaming

Games Consoles

  • PlayStation 4
  • Xbox One
  • Wii U
  • PlayStation 3
  • Xbox 360

What comes after HD?

So if HD basically refers to the now commonplace 1080p resolution, what's next?

Well that's where 4K comes in!

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