METHOD AND APPARATUS FOR TILE-RELATIVE ADDRESSING IN VIDEO CODING TECHNICAL FIELD BACKGROUND [0001] An example embodiment relates generally to video encoding and decoding. [0002] In some video codecs, such as a High Efficiency Video Coding (HEVC) codec, video pictures are divided into coding units (CU) covering the area of the picture. A CU consists of one or more prediction units (PU) defining the prediction process for the samples within the CU and one or more transform units (TU) defining the prediction error coding process for the samples in the CU. A CU consists of a square block of samples with a size selectable from a predefined set of possible CU sizes. A CU with the maximum allowed size may be named as LCU (largest coding unit) or coding tree unit (CTU) and the video picture is divided into non-overlapping LCUs. An LCU can be further split into a combination of smaller CUs, e.g. by recursively splitting the LCU and resultant CUs. Each resulting CU may have at least one PU and at least one TU associated with the CU. Each PU and TU can be further split into smaller PUs and TUs in order to increase granularity of the prediction and prediction error coding processes, respectively. Each PU has prediction information associated with the PU defining the kind of prediction that is to be applied for the pixels within the PU (e.g., motion vector information for inter predicted PUs and intra prediction directionality information for intra predicted PUs). [0003] A slice is an integer number of CTUs contained in one independent slice segment and all subsequent dependent slice segments (if any) that precede the next independent slice segment (if any) within the same access unit. In HEVC, a slice header is defined to be the slice segment header of the independent slice segment that is a current slice segment or is the independent slice segment that precedes a current dependent slice segment, and a slice segment header is defined to be a part of a coded slice segment containing the data elements pertaining to the first or all coding tree units represented in the slice segment. The CUs are scanned in the raster scan order of LCUs within tiles or within a picture, if tiles are not in use. Within an LCU, the CUs have a specific scan order. The position of a slice within a picture is indicated through block indexing in raster scan order within a picture. [0004] Because the position of a slice within a picture is indicated through block indexing in raster scan order within a picture, repositioning of a slice or extracting a subset of tiles or slices (other than picture-wide subsets starting from the top-left comer of the picture) requires