1. A video decoding method comprising: obtaining, from a bitstream, a split transformation flag indicating whether a transformation unit included in a coding unit is split; determining a size of at least one transformation unit based on the split transformation flag; determining a context model based on the size of the at least one transformation unit and a color component of a picture to which the at least one transformation unit belongs; obtaining a transformation coefficient flag indicating whether there exists a non-zero coefficient in the at least one transformation unit by entropy decoding the bitsteam based on the context model; and obtaining a transformation coefficient included in the at least one transformation unit based on the transformation coefficient flag.