A data processing apparatus is provided which is configured to receive a down-sampled source block and a down-sampled reference frame portion. The data processing apparatus comprises interpolation circuitry configured to interpolate between pixels of the down-sampled reference frame portion to generate a set of interpolated down-sampled reference frame blocks. Cost function calculation circuitry calculates a cost function value indicative of a difference between the down-sampled source block and each interpolated down-sampled reference frame block. Minimisation circuitry identifies the lowest cost function value and estimation motion vector generation circuitry generates an estimate motion vector independence thereon.