1. A method of encoding images, comprising: receiving a sequence of images; encoding the received sequence of images to produce a bitstream; and processing at least one encoded image to generate a reconstructed image usable as a reference image for the encoding of another image, the processing comprising loop filtering; wherein the loop filtering comprises: determining which images of said sequence of images are enabled images on which area-by-area loop filtering is to be enabled, permitting different image areas within the same enabled image to have different loop filtering selections, and which images of said sequence of images are disabled images on which area-by-area loop filtering is to be disabled, different image areas within the same disabled image not being permitted to have different loop filtering selections; performing area-by-area loop filtering on each said enabled image of the sequence and disabling such area-by-area loop filtering on each said disabled image of the sequence; producing a measure of the area-by-area loop filtering activity in one or more images, said measure being dependent on the loop filtering selections for the image areas of said one or more images in the case of enabling area-by-area loop filtering thereon; and determining that at least one image of said sequence is an enabled image or a disabled image in dependence upon the measure, wherein producing the measure comprises determining a number of image areas within an image, including consecutive and non-consecutive image areas, in which use of loop filtering is selected.