An image decoding method by an image decoding apparatus, the method comprising: receiving video information comprising intra luma prediction mode information and intra chroma prediction mode information; determining an intra prediction mode of a luma block based on the intra luma prediction mode information; obtaining an intra prediction mode of a chroma block related to the luma block based on the intra chroma prediction mode information, wherein the intra chroma prediction mode information indicates one of intra chroma prediction mode indices, wherein the intra prediction mode of the chroma block is determined based on the indicated one of the intra chroma prediction mode indices and the intra prediction mode of the luma block; and generating a predicted block of the chroma block based on the obtained intra prediction mode of the chroma block, wherein the intra chroma prediction mode information represents a binary code related to the one of intra chroma prediction mode indices comprising: - a first index related to a planar mode for the intra prediction mode of the chroma block, - a second index related to a vertical mode for the intra prediction mode of the chroma block, - a third index related to a horizontal mode for the intra prediction mode of the chroma block, - a fourth index related to a DC mode for the intra prediction mode of the chroma block and - a fifth index representing that the intra prediction mode of the chroma block is same as the intra prediction mode of the luma block, and wherein a first one bit of the binary code for the intra chroma prediction mode information is decoded based on a context based decoding and remaining bits of the binary code are decoded based on a bypass decoding, and wherein the binary code for the intra chroma prediction mode information is one of candidate binary codes comprising a binary code for the first index which is represented by '100', a binary code for the second index which is represented by '101', a binary code for the third index which is represented by '110', a binary code for the fourth index which is represented by '111', and a binary code for the fifth index which is represented by '0'. receiving video information comprising intra luma prediction mode information and intra chroma prediction mode information; determining an intra prediction mode of a luma block based on the intra luma prediction mode information; obtaining an intra prediction mode of a chroma block related to the luma block based on the intra chroma prediction mode information, wherein the intra chroma prediction mode information indicates one of intra chroma prediction mode indices, wherein the intra prediction mode of the chroma block is determined based on the indicated one of the intra chroma prediction mode indices and the intra prediction mode of the luma block; and generating a predicted block of the chroma block based on the obtained intra prediction mode of the chroma block, wherein the intra chroma prediction mode information represents a binary code related to the one of intra chroma prediction mode indices comprising: - a first index related to a planar mode for the intra prediction mode of the chroma block, - a second index related to a vertical mode for the intra prediction mode of the chroma block, - a third index related to a horizontal mode for the intra prediction mode of the chroma block, - a fourth index related to a DC mode for the intra prediction mode of the chroma block and - a fifth index representing that the intra prediction mode of the chroma block is same as the intra prediction mode of the luma block, and - a first index related to a planar mode for the intra prediction mode of the chroma block, - a second index related to a vertical mode for the intra prediction mode of the chroma block, - a third index related to a horizontal mode for the intra prediction mode of the chroma block, - a fourth index related to a DC mode for the intra prediction mode of the chroma block and - a fifth index representing that the intra prediction mode of the chroma block is same as the intra prediction mode of the luma block, and wherein a first one bit of the binary code for the intra chroma prediction mode information is decoded based on a context based decoding and remaining bits of the binary code are decoded based on a bypass decoding, and wherein the binary code for the intra chroma prediction mode information is one of candidate binary codes comprising a binary code for the first index which is represented by '100', a binary code for the second index which is represented by '101', a binary code for the third index which is represented by '110', a binary code for the fourth index which is represented by '111', and a binary code for the fifth index which is represented by '0'.