Computers deal with RGB color spaces, mixing red, green, and blue combinations to render onscreen colors.
But RGB isn’t suitable for storage and transmission as it carries redundancy.
Thankfully, human perception can be fooled with a technique known as chroma subsampling.
This helps reduce file size and bandwidth usage.
What Is Chroma Subsampling?
What Does It Do?
Image credit:Janke/Wikimedia Commona
The human visual system has a much lower understanding of changes in color differences than brightness.
In other words, color components are sampled at a lower resolution than brightness.
Reducing color information allows a video signal to travel efficiently via limited-bandwidth HDMI cables and over the internet.
Chroma subsampling is also used in JPEG encoding.
Their combination, known as YCbCr, is what defines the colors you see on the screen.
For example, the 4:2:2 scheme defines a segment of four pixels horizontally in two rows.
Image credit:Janke/Wikimedia Commona
It samples four luma elements and mixes them with two chroma ones (one Cr and one Cb).
4:4:4, 4:2:2, and 4:2:0: What’s the Difference?
This is why most digital video cameras and many Blu-ray movies use 4:2:0 encoding.
Chroma Subsampling in Text, Apps, and Media
Different chroma subsampling modes target specific use cases.
No one likes seeing compression artifacts on high-contrast, pixel-perfect content such as text atop a flat color.
That’s why computers, phones, tablets, and gaming consoles exclusively use the 4:4:4 sampling.
Encoding media with 4:4:4 is overkillthere’s no discernible visual difference, and file size goes through the roof.
Open this picture on a computer or view it on your TV.
If none are present, your TV uses the no-compression 4:4:4 sampling mode.
As a rule of thumb, your HDMI cables should support both 4:2:0 and 4:2:2.
For media streamers like the Apple TV, set your HDMI signal output toYCbCrin options.
