1. An inter-layer decoding method comprising: reconstructing a color image and a depth image of a first layer, based on encoding information about the color image and the depth image of the first layer, wherein the encoding information is obtained from a bitstream; determining, from the depth image of the first layer, a sub block of a depth image block of the first layer which corresponds to a sub block of a current block of a second layer image; determining whether an area included in the sub block of the determined depth image block of the first layer deviates outside of a boundary of the depth image of the first layer; when the area included in the sub block of the depth image block deviates outside of the boundary, determining a depth value of the area deviating outside of the boundary of the depth image by setting a coordinate of the area included in the sub block of the depth image block to correspond to a coordinate of the boundary of the depth image of the first layer; determining a disparity vector indicating a corresponding sub block of the first layer with respect to the sub block of the current block, by using a depth value of a pixel among depth values of pixels adjacent to four vertices of the sub block of the depth image block, wherein the depth value of the pixel is a depth value of a pixel included in the area included in the sub block of the depth image block, a coordinate of the pixel is determined to be set to correspond to the coordinate of the boundary of the depth image of the first layer; and reconstructing the current block by using the disparity vector.