A method for decoding an image, comprising: inducing a chroma component block corresponding to a luma component block based on chroma format information that indicates a chroma component sampling corresponding to a luma component sampling; partitioning the chroma component block into a transform block for the chroma component to transform the chroma component block based on partition information that represents whether a first block is partitioned into four second blocks for performing transform; and acquiring residual information of a transform block for the chroma component by performing at least one of inverse transform and dequantization based on the transform block for the chroma component, in the step of inducing the chroma component block, if the chroma format information indicates 4:2:2 chroma format and a size of the luma component block is 2Nx2N, the chroma component block is induced to Nx2N size, characterized in that the step of partitioning the chroma component block into a transform block for the chroma component includes: constructing a chroma component block of 2Nx2N size by adding a dummy block of Nx2N size to the chroma component block of Nx2N size; and partitioning the chroma component block of 2Nx2N size into four transform blocks of NxN size if the partition information indicates that the first block is partitioned into four second blocks, wherein the dummy block is a block having zero value, and wherein the transform block of NxN size which is partitioned from the dummy block does not perform the inverse transform. inducing a chroma component block corresponding to a luma component block based on chroma format information that indicates a chroma component sampling corresponding to a luma component sampling; partitioning the chroma component block into a transform block for the chroma component to transform the chroma component block based on partition information that represents whether a first block is partitioned into four second blocks for performing transform; and acquiring residual information of a transform block for the chroma component by performing at least one of inverse transform and dequantization based on the transform block for the chroma component, in the step of inducing the chroma component block, if the chroma format information indicates 4:2:2 chroma format and a size of the luma component block is 2Nx2N, the chroma component block is induced to Nx2N size, in the step of inducing the chroma component block, if the chroma format information indicates 4:2:2 chroma format and a size of the luma component block is 2Nx2N, the chroma component block is induced to Nx2N size, characterized in that the step of partitioning the chroma component block into a transform block for the chroma component includes: constructing a chroma component block of 2Nx2N size by adding a dummy block of Nx2N size to the chroma component block of Nx2N size; and partitioning the chroma component block of 2Nx2N size into four transform blocks of NxN size if the partition information indicates that the first block is partitioned into four second blocks, wherein the dummy block is a block having zero value, and wherein the transform block of NxN size which is partitioned from the dummy block does not perform the inverse transform. constructing a chroma component block of 2Nx2N size by adding a dummy block of Nx2N size to the chroma component block of Nx2N size; and partitioning the chroma component block of 2Nx2N size into four transform blocks of NxN size if the partition information indicates that the first block is partitioned into four second blocks, wherein the dummy block is a block having zero value, and wherein the transform block of NxN size which is partitioned from the dummy block does not perform the inverse transform.