Life is full of situations where it makes sense to just take a shortcut, right?
I mean how many of us are guilty of just sticking a vase on top of a scratch table instead of
refinishing the thing? And so it is with video signals. Most of the things we consume on our
screens are compressed in some fashion in order to prevent overwhelming our connections, and today
we're going to talk about a special kind of compression called chroma subsampling.
No, this is not when you decide to try a bunch of sandwiches at once, but rather refers to a
technique that takes advantage of the fact that our eyes are more sensitive to differences in
light than differences in color. Think about what it's like to watch a black and white movie,
although you might miss the colors, it's still very easy to tell exactly what's going on on the
screen, right? So chroma subsampling throws out some of the video feed's color data in order to
allow for more luminance information. So that means the picture has enough contrast to remain clear
to us while using much less video bandwidth. But how does this work? Well, when you're looking at
chroma subsampling specifications, you might see numbers like 422 or 420. This basically means
that if you take a 4 by 2 block of pixels, only one half or one quarter, respectively, of the
original color data will be retained. The luminance data for each pixel is retained fully, that's the
but applied to only one half or one quarter as many colors.
Chroma subsampling is a widespread standard for movies and TV, which typically use the 420 method.
It's a big part of the reason you can watch 4K Netflix or YouTube without a constantly
buffering. And even non-streaming options like home Blu-ray players make frequent use of it.
And although this might sound like you'll end up not seeing accurate colors, our eyes simply
can't tell the difference in many cases. Given that a 420 subsampled video file only takes up
about as half as much space as an uncompressed or 444 file, it's not surprising that it's very
commonly used. But are there times when 444 is actually important to have? The answer is yes,
especially if your screen is connected to a computer. You see, chroma subsampling is fine for
content with smooth gradations like movies and sporting events and even many video games.
But if the display you have hooked up to your PC is subsampling, text and other UI elements with
sharp edges can look smudged and blurry. This typically is not an issue for actual computer
monitors as these are usually designed to display a 444 signal. But televisions are notorious for
undesirable subsampling, which you may have seen for yourself if you've ever tried to type a word
document or read an article in your browser on your living room TV. An artifact sometimes called
fringing. Pretty hard to read, depending on the background color. Nowadays, though, many modern
TVs can be specifically told that they're connected to a PC and therefore should not subsample.
Typically, if you can locate a setting called something like UHD color, deep color, RGB,
or something similar, switching to it should force the TV to display your images in 444.
Other times, simply selecting a PC or computer mode on your TV will also do the trick. But if
you're connecting your computer to your TV to enjoy high bandwidth features like 4K at 120Hz
or HDR, make sure the television can support these bells and whistles simultaneously with 444.
Recently, there was a bit of a scandal with one of LG's OLED TV lineups because the TVs
would chroma subsample when set to 4K120, resulting in bad looking text when connected to a PC.
Even though the display's HDMI 2.1 ports should have delivered enough bandwidth to not have to
subsample. LG fixed the issue with a firmware update, I guess, but this is just the kind of stuff you
can expect when you're bold enough or rich enough to be an early adopter. So thanks for watching,
guys. If you liked this video, give it a thumbs up, hit subscribe, and check us out. Hit us up in
the comments section with your own original ideas of topics that we should cover in the future.