Chroma Subsampling: Everything You Need to Know

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chroma subsampling
Behind the scenes of your favorite films and television shows, hours and hours of work (equaling months) is put in to achieve the final result. This is not just limited to the writing, directing, and producing, however, but also in bringing the end product to you: DVDs, rentable downloads, and streaming services all work hard to make the at-home experience as enjoyable for the viewer as technologically possible.

You might already know (or want to know) a little bit about the color depth and image quality of screens, and how it affects what you see on the screen, potentially enhancing the experience if you know what you’re doing.

In the trade-off between quality, affordability, and speed, there’s also the issue of image compression, both a solution and a problem, both of them in the obvious sense. Despite proper calibration, even the best gaming monitors can seem to display artifacts of compression, while file sizes for games get bigger and bigger.

More data can be sent by manufacturers and content providers, using less bandwidth. This makes everything cheaper, faster, and as HD or Ultra HD as it can get, but at the same time, we run a risk of losing definition.

Enter chroma subsampling: we know from our experience, that whatever video we watch or download is ultimately very high quality, and that file sizes for video have gone down over the years. This is achieved largely thanks to increased efficiency in the same systems of digital communication through techniques such as chroma subsampling.

What Does Chroma Subsampling Do?

We’ve said the name a few times, but to define it and unpack why it’s named this way will require a little backstory, which we’ll get into in the next few sections.

Ultimately, we talk about chroma subsampling for its practicality; bandwidth is reduced, processing power becomes strengthened, meaning you need less of it to do more of the same, allowing streaming giants to become the powerhouses that they have.

What Is Chroma Subsampling?

Video signals consist of two “aspects” of information: color and luminance. Luminance rules contrast, which in turn defines what you see – think of how detailed a black and white image can be, even without any color information (alternatively called chrominance or, in a more recognizable shorthand, chroma).

Hence, chroma subsampling, as a form of data compression, works by optimizing the video signal such that the reduced color information is made up for by luminance data. This means that bandwidth is saved without compromising on the quality of the image. The clarity of the picture is preserved, and the file size can be cut – sometimes up to half of the original size – making data transfer and bandwidth usage much more efficient, enhancing the capabilities of both broadband and HDMI.

How Does Chroma Subsampling Work?

Human eyes are more sensitive to luminance – or brightness – than the color itself, thus owing to the success of chroma subsampling. Every single pixel still includes luminance information, but chroma information is shared between pixels adjacent to each other.

This is how the different types of chroma subsampling are created: the ratio described is one of 4 pixels across and 2 high, totaling a block of 8 pixels, represented in x:x:x notation. The first number indicates the width of the sample in pixels, and the second and third tells us how many pixels have chroma samples in the top and bottom row, respectively.

However, more color information is not necessarily needed, or better, which is why 4:4:4 is considered to be high-end, with 4:2:2 being the industry standard for professional video, and 4:2:0 being used for Ultra HD Blu-rays even in the latter half of this decade.

Some of the best 4K televisions out there, however, support 4:4:4 with at least one HDMI input, which is good news for those who gaming setups are connected with their TV sets. If not, a home theater receiver can be used, especially in the case of almost all receivers out there with HDCP 2.2.

How Do We Test For Chroma Subsampling?

It’s easy to pick up on the presence of chroma subsampling with the help of this test pattern from RTINGs, which can be opened in a browser or pasted into an image editor.

If the text or the lines blur together, it’s a show of ‘artifact-ing’, meaning that the chroma is 4:4:4 – no chroma subsampling is present. However, it’s good to control for a false positive. Make sure that Window’s scaling is set to 100% – with larger monitors displaying at high resolutions, UI elements can be scaled automatically at 150% or more.

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