Method and device for subband coding frequency conversion unit, and method and device for image encoding/decoding using same

A video encoding method for encoding residual signals in a two dimensional frequency conversion unit having a size larger than or equal to 8×8 pixel size, the frequency conversion unit being a unit of transforming the residual signals that are differences between original pixel values and predicted pixel values, the method comprising:

• transforming the residual signals from a spatial domain into a frequency domain by using a transform size identical to the size of the frequency conversion unit, to generate a frequency conversion block having the size of the frequency conversion unit;
• and
• encoding frequency coefficients in the frequency conversion block in the unit of two dimensional subblocks divided from the frequency conversion block, all of the subblocks divided from the frequency conversion block being equal-sized square blocks which have a 4×4 pixel size regardless of the size of the frequency conversion block,
• wherein the encoding of the frequency coefficients comprises:
• encoding subblock encoding information indicating whether a subblock of the 4×4 pixel size in the frequency conversion unit corresponding thereto has at least one non-zero frequency coefficient, wherein:
• a value of the subblock encoding information is 0 when the subblock does not have at least one non-zero frequency coefficient, and
• the value of the subblock encoding information is 1 when the subblock has at least one non-zero frequency coefficient;
• encoding frequency coefficients corresponding to the subblock, when the subblock encoding information indicates that the subblock has at least one non-zero frequency coefficient,
• wherein, when the subblock encoding information indicates that the subblock does not have at least one non-zero frequency coefficient, the frequency coefficients corresponding to the subblock are not encoded,
• wherein each of the subblocks includes frequency coefficients corresponding to a frequency range, the frequency range of each of the subblocks being different from each other,
• wherein the frequency coefficients which are located at different positions in each of the subblocks are values in the frequency domain which correspond to different frequencies.

A non-transitory recording medium storing a bitstream containing encoded data of frequency coefficients of a two dimensional frequency conversion unit having a size larger than or equal to 8×8 pixel size, the frequency conversion unit being a unit of transforming residual signals that are differences between original pixel values and predicted pixel values, the bitstream be decoded by a process comprising:

• reconstructing the frequency coefficients of the two dimensional frequency conversion unit by decoding a bitstream, thereby generating a frequency conversion block having a size of the two dimensional frequency conversion unit, wherein the frequency coefficients is values generated by transform of the residual signals from a spatial domain into a frequency domain;
• and
• inversely transforming the frequency conversion block from the frequency domain to the spatial domain, by using a transform size identical to the size of the two dimensional frequency conversion unit,
• wherein the frequency conversion block is generated by reconstructing and inversely scanning the frequency coefficients of the two dimensional frequency conversion unit in the unit of two dimensional subblocks divided from the two dimensional frequency conversion unit, all of the subblocks in the two dimensional frequency conversion unit having a 4×4 pixel size irrespective of the size of the two dimensional frequency conversion unit,
• wherein the reconstructing and inversely scanning of the frequency coefficients in the unit of the subblocks comprises:
• decoding, from the bitstream, subblock encoding information indicating whether a subblock of the 4×4 pixel size corresponding thereto has at least one non-zero frequency coefficient, wherein,
• a value of the decoded subblock encoding information is 0 when the subblock does not have at least one non-zero frequency coefficient, and
• the value of the decoded subblock encoding information is 1 when the subblock has at least one non-zero frequency coefficient,
• reconstructing from the bitstream and inversely scanning frequency coefficients corresponding to the subblock, when the decoded subblock encoding information has a value of 1, and
• setting all frequency coefficients corresponding to the subblock to 0, when the decoded subblock encoding information has a value of 0,
• wherein each of the subblocks includes frequency coefficients corresponding to a frequency range, the frequency range of each of the subblocks being different from those of another subblocks,
• wherein the frequency coefficients which are located at different positions in each of the subblocks are values in the frequency domain which correspond to different frequencies.