Tech Tips - Televisions: HD or UHD that is the question 


What is HD?

HD or High Definition has been around for quite some time now. It will refer to the resolution that the TV/Monitor is capable of displaying. In simple terms resolution represents the number of horizontal lines a video has from top to bottom. 

So, a 1080p video is made up of 1080 lines stacked one on top of another, with each line being 1920 pixels wide. In other words, a 1080p video has a resolution of 1920×1080 pixels. 

What is a Pixel? 

A 'pixel' (short for 'picture element') is a tiny square of colour. Lots of these pixels together can form a digital image. If you put 1920 pixels wide on 1080 lines you then see the image in 1920x1080 resolution or as it is often referred to 1080p. 

What is UHD or Ultra High Definition? 

This often used to refer to a 4K resolution 

What is 4K? 

This again refers to a resolution. In this case 3840x 2160. So, 3840 pixels wide and 2160 lines. So how does that make a difference? More lines and more pixels increase the sharpness and detail. 4K is four times the pixel resolution, or twice the line resolution (2160p), of 1080p (1920 x 1080 pixels) 

What is 4K 4096x2160? 

 This resolution mainly used in Digital Cinema production. 

What is HDR? 

Link to HDR FAQ’s 

Why do your products mention 10.2G and 18G? 

Here we are referring to the data carrying capabilities of devices such as extenders, switches and splitters etc. 

10.2G is the maximum Bandwidth the device can operate at. This would normally refer to 1080p devices but under certain circumstances it can also carry 4K.   

Sending video to a screen is not just concerned with Lines and Pixels. We have to consider other factors and these a refresh rate and colour space.  

What is Refresh rate? 

Refresh rate is measured in frequency (Hz) which is the number of times per second your monitor can redraw the screen. To use 4K with a 10.2G device you would need to have a refresh rate of 30Hz rather than the 60Hz you can use with 4K on 18G devices. You are effectively reducing the amount of data that will be sent to the screen, and there is another way to do it. 

What is 4:4:4 and 4:2:0? 

In order to use 4K on 10.2G devices we can also look at the colour space or chroma subsampling. 

A signal with chroma 4:4:4 has no compression (so it is not subsampled) and transports both luminance and colour data entirely. In a four by two array of pixels, 4:2:2 has half the chroma of 4:4:4, and 4:2:0 has a quarter of the colour information available. The 4:2:2 signal will have half the sampling rate horizontally, but will maintain full sampling vertically. 4:2:0, on the other hand, will only sample colours out of half the pixels on the first row and ignores the second row of the sample completely. 

So, we are using a form of compression to reduce the amount of data we send. 

Why do I need 18G? 

If you want to use 4K at a 60Hz refresh rate with no compression then you need an 18G capable devices.  

If you want to use 4K Sky or Virgin boxes you will also need to use 18G equipment as these use HDR (link) which sends more data than 10.2G.