A method of decoding residual coefficients of a transform unit from a bitstream of video data, the method comprising: receiving the transform unit from the bitstream of video data, the transform unit having upper level and lower level square layers, wherein the upper level square layer represents a square region for arrangement of significant coefficient group flags, each of which indicates whether at least one of residual coefficients within a corresponding non-overlapping 4x4 square region of the lower level square layer is significant, and the lower level square layer represents 8x8 square region including a plurality of non-overlapping 4x4 square regions for arrangements of residual coefficients, and wherein significant coefficient flags for indicating whether a corresponding residual coefficient is significant are encoded in the bitstream; determining a scan pattern (1501,1601,1701) for the upper level square layer and the lower level square layer according to an intra-prediction mode; determining the significant coefficient group flags corresponding to respective 4x4 non-overlapping square regions of the lower level square layer for the received transform unit in a scan order corresponding to the determined scan pattern (1501,1601,1701); and determining values of residual coefficients of the lower level square layer according to the determined significant coefficient group flags and a scan order corresponding to the determined scan pattern (1501,1601,1701) of the residual coefficients to decode the transform unit of the bitstream of video data, wherein the scan pattern (1501,1601,1701) for the significant coefficient group flags and the residual coefficients is determined from a first scan pattern, a second scan pattern, and a third scan pattern, according to the intra-prediction mode, and the first scan pattern, the second scan pattern, and the third scan pattern are different from each other. receiving the transform unit from the bitstream of video data, the transform unit having upper level and lower level square layers, wherein the upper level square layer represents a square region for arrangement of significant coefficient group flags, each of which indicates whether at least one of residual coefficients within a corresponding non-overlapping 4x4 square region of the lower level square layer is significant, and the lower level square layer represents 8x8 square region including a plurality of non-overlapping 4x4 square regions for arrangements of residual coefficients, and wherein significant coefficient flags for indicating whether a corresponding residual coefficient is significant are encoded in the bitstream; determining a scan pattern (1501,1601,1701) for the upper level square layer and the lower level square layer according to an intra-prediction mode; determining the significant coefficient group flags corresponding to respective 4x4 non-overlapping square regions of the lower level square layer for the received transform unit in a scan order corresponding to the determined scan pattern (1501,1601,1701); and determining values of residual coefficients of the lower level square layer according to the determined significant coefficient group flags and a scan order corresponding to the determined scan pattern (1501,1601,1701) of the residual coefficients to decode the transform unit of the bitstream of video data, the scan pattern (1501,1601,1701) for the significant coefficient group flags and the residual coefficients is determined from a first scan pattern, a second scan pattern, and a third scan pattern, according to the intra-prediction mode, and the first scan pattern, the second scan pattern, and the third scan pattern are different from each other.