in video encoding it is common to encode the image data to remove redundancies in the information to be transmitted . while the pixel data is usually arranged in pixel blocks , the blocks can be arranged in one or more groups of n × m blocks called tiles . the tiles avoid the need to send header information on a tile - by - tile or block - by - block basis , and simplifies parallel processing of the tiles . bits from respective tiles may then be reformatted to recreate bits according to a raster - scan direction . this enables the decoder to receive the bits in a regular raster - scan format , but also have the ability to decode the tiles once the bits are reformatted . by partitioning an image into tiles of size n × m , it is possible to further exploit the intra - frame correspondence of images in a vertical direction as well as horizontal direction since the tiles need not destroy as many dependencies between blocks in a tile as if the blocks where organized in slices or slice groups .