Wikipedia has a decent article with visuals: https://en.wikipedia.org/wiki/Chroma_subsampling#Sampling_systems_and_ratios https://en.wikipedia.org/wiki/Chroma_s

Wikipedia has a decent article with visuals: https://en.wikipedia.org/wiki/Chroma_subsampling#Sampling_systems_and_ratios https://en.wikipedia.org/wiki/Chroma_subsampling#Sampling_sy... The difference between 4:1:1 and 4:2:0 is that in 4:1:1 the chroma covers a 1x4 line of pixels whereas in 4:2:0 the chroma covers a 2x2 square of pixels.