1. A motion estimation unit ( 100 ) for generating a motion vector ( 126 ) corresponding to a block ( 116 ) of pixels of an image ( 118 ), comprising: a block-matcher ( 102 ) for calculating a start motion vector ( 110 ) by minimizing a predetermined cost function as a matching criterion for matching the block ( 116 ) of pixels with a further block of pixels ( 122 ) of a further image ( 120 ); an optical flow analyzer ( 104 ) for calculating an update motion vector ( 111 ) based on the start motion vector ( 110 ) and based on a first optical flow equation for a first pixel of the block ( 116 ) of pixels; and a selector ( 106 ) to select as the motion vector ( 126 ), the start motion vector ( 110 ) or the update motion vector ( 111 ), by comparing a first value of the matching criterion of the start motion vector ( 110 ) with a second value of the matching criterion of the update motion vector ( 111 ), characterized in that the optical flow analyzer ( 104 ) is designed to select the first pixel and a second pixel from the block ( 116 ) of pixels to solve a set of equations comprising the respective first optical flow equation and a second optical flow equation, with the selecting based on a first gradient vector of the first optical flow equation and a second gradient vector of the second optical flow equation.