Ever feel lost when talking about Chroma Subsampling, 4:4:4, 4:2:2, 4:2:0, 4:1:1? If so, bookmark this link and refer back as a refresher. It's just an incredibly well illustrated article that helps you visually understand the differences happening with each type of sampling. A small excerpt from the article:
Using the standard nomenclature, 4:2:2 means each horizontal scanline has 2 chroma values for every 4 luma values. Similarly, 4:1:1 means 1 chroma value is sent for every 4 luma values sent, and 4:4:4 means no chroma subsampling. However, this is not entirely consistent. 4:2:0 would imply that for every 4 luma values, there would be 2 for the first chroma component and 0 for the second—but this wouldn’t produce full color images. In practice, 4:2:0 instead means there are two of each chroma sample per scanline, but that these are only present every other line.