1. A method of using a processor to provide an assessment of picture impairment due to the interpolation of an output image in a sequence of output images from at least two input images in a sequence of input images, the method comprising the steps of: receiving at the processor said sequence of input images; forming at least one input image detail measure from each input image; receiving at the processor said sequence of output images; forming at least one output image detail measure from each output image; interpolating image detail measures using image detail measures from at least two input images or at least two output images; and comparing an image detail measure from one of the input or output image sequences with an interpolated image detail measure from the other of the input or output image sequences.