An image encoder or other image processing apparatus includes a segmentation apparatus for assigning image pixels to regions, in accordance with predetermined criteria. The segmentation apparatus provides a temporally consistent segmentation throughout a motion picture sequence, and comprises: a motion compensation processor for predicting the segmentation for a current frame (F0) upon the basis of the segmentation (S1) of the preceding frame and estimated motion vectors (M); a pixel identifier and reallocator for modifying the predicted segmentation in dependence upon the accuracy of pixel values (F0') predicted for the current frame on the basis of the motion vectors (M). In particular, for portions of the image where pixel values are not accurately predicted by the motion vectors, it is assumed that the predicted segmentation is invalid, and such portions are re-segmented and merged into the predicted segmentation to obtain the temporally consistent segmentation. In the embodiments, pixels on the borders of regions in the predicted segmentation are also considered and re-assigned to neighbouring regions according to various criteria.
