An image decoding method performed by an image decoding apparatus, the image decoding method comprising: obtaining a current block by splitting an image; determining a prediction mode of the current block; generating an intra prediction block of the current block, based on the prediction mode of the current block being an intra prediction mode; generating a residual block of the current block; and reconstructing the current block based on the intra prediction block and the residual block of the current block, characterized in that: the intra prediction block and the residual block are generated based on a size of a transform block of the current block, based on a color component of the current block being a chroma component, a maximum width of the transform block is derived by dividing a maximum size of a luma transform block corresponding to the current block by a ratio of a width of a luma block to a width of a chroma block, the ratio being determined based on a color format of the current block, based on the color component of the current block being the chroma component, a maximum height of the transform block is derived by dividing the maximum size of the luma transform block corresponding to the current block by a ratio of a height of the luma block to a height of the chroma block, the ratio being determined based on the color format of the current block, the maximum width of the transform block is compared to a width of the transform block to determine whether to split the transform block vertically, and the maximum height of the transform block is compared to a height of the transform block to determine whether to split the transform block horizontally. obtaining a current block by splitting an image; determining a prediction mode of the current block; generating an intra prediction block of the current block, based on the prediction mode of the current block being an intra prediction mode; generating a residual block of the current block; and reconstructing the current block based on the intra prediction block and the residual block of the current block, characterized in that: the intra prediction block and the residual block are generated based on a size of a transform block of the current block, based on a color component of the current block being a chroma component, a maximum width of the transform block is derived by dividing a maximum size of a luma transform block corresponding to the current block by a ratio of a width of a luma block to a width of a chroma block, the ratio being determined based on a color format of the current block, based on the color component of the current block being the chroma component, a maximum height of the transform block is derived by dividing the maximum size of the luma transform block corresponding to the current block by a ratio of a height of the luma block to a height of the chroma block, the ratio being determined based on the color format of the current block, the maximum width of the transform block is compared to a width of the transform block to determine whether to split the transform block vertically, and the maximum height of the transform block is compared to a height of the transform block to determine whether to split the transform block horizontally. the intra prediction block and the residual block are generated based on a size of a transform block of the current block, based on a color component of the current block being a chroma component, a maximum width of the transform block is derived by dividing a maximum size of a luma transform block corresponding to the current block by a ratio of a width of a luma block to a width of a chroma block, the ratio being determined based on a color format of the current block, based on the color component of the current block being the chroma component, a maximum height of the transform block is derived by dividing the maximum size of the luma transform block corresponding to the current block by a ratio of a height of the luma block to a height of the chroma block, the ratio being determined based on the color format of the current block, the maximum width of the transform block is compared to a width of the transform block to determine whether to split the transform block vertically, and the maximum height of the transform block is compared to a height of the transform block to determine whether to split the transform block horizontally.