There are three types of chroma subsampling supported by AVIF: 4:2:0, 4:2:2, and 4:4:4. Encoding images uses less resolution for chroma information than for luma information due to a lower understanding of color differences than that of luminance differences. In cases where the loss caused by 420 subsampling is not apparent to the human eye, 420 subsampling can be beneficial.
What chroma subsampling does AVIF support?
Primary sources1. AVIF - The Full Guide and FAQ2. AVIF AOMedia Specification3. AVIF Wikipedia4. Jake Archibald Article5. AVIF Netflix article