1. A video signal processing method, comprising: obtaining a boundary intra coding flag whether a current block is coded by using boundary intra coding; based on the boundary intra coding flag indicating that the current block is coded in an intra prediction mode by using the boundary intra coding, deriving a partition line of the current block based on a base pixel and a boundary code for at least one pixel located on the partition line, the base pixel being a starting point of the partition line, and the boundary code including information indicating whether a turning direction of a current pixel is equal to a turning direction of a previous pixel and a turning angle of the current pixel, the current pixel and the previous pixel being located on the partition line, the partition line being a boundary of a region having a pixel value different from a pixel value of a neighboring region, wherein the current block divides into A region and B region based on the partition line; and decoding each of the regions in the current block including the A region and the B region, wherein deriving the partition line of the current block comprises: obtaining the base pixel, the boundary code and information about the number of the boundary pixels; and deriving a location of boundary pixels using the base pixel, the boundary code and the information about the number of the boundary pixels, wherein the A region is decoded using a intra prediction mode of the A region being different from a intra prediction mode of the B region.