1. An apparatus, comprising: a transform circuit configured, to receive input blocks of an image, each input block representing a portion of the image in a first domain and at a first resolution, and to generate in response to each input block a respective transformed block representing the corresponding portion of the image in a second domain; a filter configured to generate in response to each transformed block a respective filtered block; an inverse-transform circuit configured to transform each filtered block into a respective inverse-transformed block representing the corresponding portion of the image in the first domain; and a resolution converter circuit configured, to convert at least one of the inverse-transformed blocks into a respective converted block representing the corresponding portion of the image at a second resolution, and to provide each converted block to the transformer.