What does the third number in the encoding description (e.g., 4:2:0) indicate?

In encoding descriptions such as 4:2:0, the third number represents the amount of chroma information sampled relative to the luma. Specifically, it indicates how many chrominance samples are taken for every luma sample in a horizontal row. In the case of 4:2:0, the '0' signifies that no chroma samples are taken in every second row.

This encoding format is often used in video compression, where the numbers reflect the ratio of luma (brightness) to chroma (color information) components. The first number denotes the luma samples across the entire row, the second number refers to the chroma samples in the first row, and the third indicates the chroma samples in the second row. This means in 4:2:0, while you have full luma samples, you only get half of chroma samples in one of the rows, leading to a more efficient compression without significantly affecting perceived video quality.

Understanding this encoding is crucial in determining the quality and bandwidth of video streams, especially in applications like streaming and broadcasting. The choices referring to the number of pixels in specific rows or concerning total color channels do not accurately describe the function of the third number in the context of color