Is Chroma Sampling Important for Monitors?

Adopted by every organisation and manufacturer related to display, chroma sampling means interpreting colour, or chroma, as the second component of an image after luma, or light. The term subsampling denotes a need to compress or reduce from the source, or the original sample. A subsample takes the source and compresses it by reducing colour data so the image can fit via connection standards like HDMI, 802.11ac Wi-Fi, internet protocols, and so on. That’s because in many cases the original would simply be too big to transmit quickly enough. Your 4K Netflix streams are highly compressed to ensure they have 8.3 million pixels and 60 frames per second. Reducing colour data makes that possible without damaging image quality too much, because the vast majority of people don’t notice colour compression.

There’s no luma subsampling even though that is technically possible. Reducing luma or light data would simply make the overall image less visible and totally ruin the experience, so there’s obviously no way that would make sense. Colour has to be the victim in this balance sheet.

The standard sample assumes two horizontal rows of four pixels stacked on top of each other. But we have three numbers, as in 4:X:X. The first 4 is constant as it stands for light, and light is always fully sampled without compression. So the row for light is assumed and not shown in the matrix, or grid. The two that are shown represent colour sampling, so the second and third numbers stand for chroma (ostensibly blue and red, with green resulting from their mix). If we use 4:4:4 that technically means “true” or uncompressed sampling, and not subsampling. Light gets a full four pixels, and the two colour rows also each has four individual pixels sampled. That’s the closest we get to uncompressed video signals right now.

Switch to 4:2:2 and that means each colour row only has two pixels sampled. The other four are duplicated from the sample by processing components. In 4:2:0, only two pixels in the top row have colour samples, with the remaining six merely copying them and the bottom row having no pixels of its own, thus zero. Sampling less pixels leads to less data having to be delivered between devices, and hence a faster and more efficient connection.

The naming scheme also appears as YUV, YCbCr, or YPbPr. YUV equals 4:2:0 in practical terms, and most game consoles and PC graphics cards support it due to modest bandwidth requirements. 

To give you some perspective, a 4:2:0 feed requires half the data or bandwidth of 4:4:4. So that Netflix or Prime Video 4K HDR show you’re watching right now needs about 15-16Mbps in real internet bandwidth. The same content in 4:4:4 would need over 30Mbps in bandwidth, and that’s a big deal for streaming services and internet providers. Using 4:2:0 allows Netflix and others to state a 25Mbps connection is enough to subscribe. Switching to 4:4:4 would mean a 50Mbps minimum to be safe. 

It does. But as sampling puts some strain on processing power, the main consideration for manufacturers and content providers is bandwidth for connectivity. So pretty much any display you get your hands on will work with all major sampling and subsampling methods. It’s the core hardware and design of the display that matter too. In this case, colour bit depth and peak brightness as well as individual monitor/display colour calibration are factors to consider first and foremost.

We’re happy to say BenQ has you covered on all counts.