1. A method comprising: at an image processing apparatus: partitioning an image into a plurality of blocks; for a selected one of the plurality of blocks, and using a given available range of grayscale level values, determining grayscale level values for image data in the selected one of the plurality of blocks to provide determined grayscale level values; transforming at least some of the determined grayscale level values to thereby use an altered amount of the given available range of grayscale level values to thereby provide rescaled grayscale level values for the selected block.