Method and apparatus for encoding/decoding image using variable-size macroblocks

1. A video decoding apparatus for reconstructing residual signals of a current block to be decoded by using a tree structure, the apparatus comprising:

a decoder configured to

decode, from a bitstream, prediction type information on the current block to be decoded, and

divide, by the tree structure, the current block into one or more subblocks of which information on residual signals is to be reconstructed, by decoding, from the bitstream, a partition flag which indicates whether a block corresponding thereto is divided into blocks of a lower layer in the tree structure, wherein blocks which are not further divided are identified as the subblocks of which information on the residual signals is to be reconstructed; and

a reconstructor configured to reconstruct information on the residual signals of each of the subblocks from the bitstream,

wherein, when a block of a first layer in the tree structure is divided into a plurality of blocks of a second layer which is a lower layer of the first layer, the decoder is configured to decode the partition flag for each of the blocks of the second layer in a predetermined order, the predetermined order being an order of an upper left block, an upper right block, a lower left block and a lower right block, and

wherein, when a block among the blocks of the second layer is further divided into a plurality of blocks of a third layer which is a lower layer of the second layer, the decoder is configured to decode the partition flag for each of the blocks of the third layer in the predetermined order, before decoding the partition flag for a next block of the second layer in the predetermined order.

2. The video decoding apparatus of claim 1 , wherein, when the partition flag indicates that a block is divided into blocks of a lower layer, the block is divided into four equal-sized blocks of the lower layer.

3. The video decoding apparatus of claim 1 , wherein the decoder does not decode, from the bitstream, the partition flag for a block having a size identical to a minimum block size.

4. The video decoding apparatus of claim 1 , wherein a size of the current block includes 16×16, 32×32 and 64×64 pixels.

5. The video decoding apparatus of claim 1 , wherein a size of each of the subblocks is variably determined based on a size of the current block and the partition flag.

6. The video decoding apparatus of claim 1 , wherein the prediction type information indicates whether the current block is inter-predicted or intra-predicted.

7. The video decoding apparatus of claim 1 , wherein the decoder decode the prediction type information by

decoding, from the bitstream, a first information indicating whether all the subblocks in the current block are predicted using the same prediction type, and

decoding, from the bitstream, a second information indicating whether each subblock is inter-predicted or intra-predicted, when the first information does not indicate that all the subblocks in the current block are predicted using the same prediction type.

8. The video decoding apparatus of claim 1 , wherein the reconstructor is configured to

reconstruct, from the bitstream, coded block information indicating whether or not a subblock has at least one non-zero transform coefficient; and

reconstruct transform coefficients of the subblock from the bitstream when the coded block information indicates that the subblock has at least one non-zero transform coefficient, and then inversely quantize and inversely transform the reconstructed transform coefficients.

9. The video decoding apparatus of claim 1 , wherein the decoder starts to decode the partition flag from the current block on which the prediction type information is decoded.