Please improve the coherence of the following paragraph
However, CCIR 601 uses 4: 2: 2 color sampling, which subsamples the Cb and Cr components only horizontally. H. 261 used vertical color subsampling, resulting in what is known as 4: 2: 0.
However, CCIR 601 uses 4: 2: 2 color sampling, which subsamples the Cb and Cr components only horizontally. H. 261 additionally used vertical color subsampling, resulting in what is known as 4: 2: 0.