The highest-quality digital video encoding mode, which compresses all the color information in the original signal. The next mode 4:2:2 is also high quality; however, red and blue are sampled only half as much. As the numbers get lower, the color is sampled fewer times for higher compression (4:2:0, 4:1:1, etc.). For more details, see chroma subsampling.
Under the Whyte notation system, a steam locomotive that has four leading wheels arranged in a leading truck, four coupled driving wheels and four trailing wheels in a trailing truck.