1. An image analysis apparatus for processing a 3D video signal comprising successive pairs of images representing different respective views of a scene to generate an image depth indicator; the apparatus comprising: a correlator configured to correlate image areas in one of the pair of images with image areas in the other of the pair of images so as to detect displacements of corresponding image areas between the two images; a graphics generator configured to generate a graphical representation of the distribution of the displacements, with respect to a range of possible displacement values, across the pair of images; a display generator for generating for display the graphical representation in respect of a current pair of images at a current pair display position and in respect of a plurality of preceding pairs of images at other display positions, so as to provide a time-based representation of variations in the distribution of the displacements.