4:4:4 is uncompressed and therefore provides the best image quality, whereas 4:2:2 and 4:2:0 sacrifice color quality for a lower data rate.
Chroma subsampling is a type of color compression that reduces data rate and file size.
Most content nowadays, including TV shows and movies, use 4:2:0 chroma subsampling because the loss in graphical quality is practically invisible, especially at 4K, while the bandwidth compression allows for easier data transfer, including seamless streaming via services such as Netflix.
The only case where chroma subsampling becomes apparent is when you are looking at small text displayed on a colored background. The text will look blurry and fuzzy when looking at the screen up close.
This is why if you want to use a TV as a monitor, it should have a 4:4:4 mode.
How Does Chroma Subsampling Work?
In the 4×2 grid sample above, 4:4:4 represents no chroma subsampling used, whereas 4:2:2 has every other pixel duplicated, and 4:2:0 has bottom pixels copying top pixels.
So, 4:4:4 will have the best image quality, but the highest data rate – while 4:2:0 has the lowest quality picture, but also the smallest bandwidth requirements.
In the picture below, you can see how it would affect a complete picture.
How To Activate 4:4:4 On TVs?
If your TV supports 4:4:4 chroma, you can enable it by going to the settings menu and finding an option typically called HDMI UHD Color, HDMI Enhanced Format, or something along those lines, depending on the TV model.
Keep in mind that enabling 4:4:4 for 4:2:0 or 4:2:2 native content won’t enhance the image quality.
So, the only time you would actually require it is when you are playing console games or using your TV as a PC monitor.
Chroma Subsampling On Monitors
By default, graphics cards and monitors don’t use any chroma subsampling, but a full 4:4:4 range.
The only reason to use chroma subsampling is when the monitor’s connectors don’t have enough bandwidth for the maximum refresh rate and resolution of the display.
For instance, DisplayPort 1.4 has a maximum data rate of 25.92 Gbit/s.
In order to drive a 4K monitor at 120Hz with 10-bit color depth, a data rate of 32.27 Gbit/s is required.
So, you’ll need to either drop the color depth to 8-bit or lower the refresh rate to 98Hz in order not to go over the maximum bandwidth supported by DisplayPort 1.4.
Alternatively, you can use 4:2:0 chroma subsampling to get 4K 120Hz 10-bit color, but at a lower data rate (21.52 Gbit/s).
However, since all PC games use 4:4:4, you will notice visual artifacts with text, so it’s not recommended to use chroma subsampling in most games.
DSC (Display Stream Compression)
An improved form of data rate compression is DSC, which is available on some newer monitors and graphics cards (AMD Navi, NVIDIA Turing, or newer GPUs) over DisplayPort 1.4.
This type of compression doesn’t have any effect on the image quality, but rather on latency; however, the added delay is imperceptible (~1ms).