Hi there,
Thanks for checking out a 'Explained' blog! In these; my aim is to give you some details on what some common technical terms mean in digital video and film. I hope you find something useful here.
Please note; I do not consider myself an expert on the topics - if you believe I've made a mistake somewhere please do let us know! I'd love for this to be a learning experience for me as much as anyone else.
Chroma Subsampling
You may have seen values such as 4:4:4, 4:2:2, 4:2:0 etc on camera specifications, video files and elsewhere; these represent the type of chroma-subsampling being used in the compression, but how exactly does Chroma-subsampling work?
The principle behind it is based on the idea that the human eye is much more sensitive to variations in brightness than it is to colour. This is why YCbCr separates the luminance channel from the colour ones, so that chroma subsampling can take advantage of this knowledge to reduce the data of the colour information whilst preserving that of the brightness. The best way to understand how this works is through diagrams (shout out to Karl Soule, who's post on this I find to be most clear and understandable; and is also the source of these images):