1. A method of detecting noise in an image of a compound document, said image comprising pixels representing at least text data and image data used to form the compound document, said noise comprising at least one of halftone, bleeding and texture noise, the method comprising the steps of: (a) partitioning the image into a plurality of tiles each formed of a plurality of pixels; (b) determining a set of dominant colours for each said tile and associating each pixel with one of the determined dominant colours; (c) determining for each dominant colour a fragmentation statistic; and (d) applying a threshold to each said fragmentation statistic to detect the at least one of halftone, bleeding and texture noise in the corresponding dominant colour in the tile.