Image synthesis methods and units are described which can be implemented in real-time on low-cost and mobile devices. A set of sample blocks from an input image are defined. For each combination of sample blocks, a matching block is determined, which provides a best match for that combination when positioned in conjunction with a predetermined arrangement of the sample blocks of the combination. A match table can then be created and stored which includes an indication of the determined matching block for each combination of sample blocks from the input image. The match table can be used to generate a synthesised image, which may be much larger than the input image. For example, the match table may be used to determine an index table which comprises indications of sample blocks to be positioned in a synthesis arrangement for generating the synthesised image.