Abstract: An arrangement (100) for determining the position of the energy center (o') of the image (S') of a luminous object by barycentric calculation within a window (122) surrounding said image (S') and covering p.sub.l .times.p.sub.c elements of a charge-transfer matrix (120). According to the invention, the arrangement has:a first mode of operation, during which on the one hand said matrix (120) is read by grouping the N.sub.l lines m-by-m (m<p.sub.l) in the output register (121), whereas on the other hand, the output register (121) is emptied by grouping, in the read arrangement (123) of the matrix (120), l (l<p.sub.c) consecutive elements from the output register (121), so as to determine the brightest zone m.times.l (124) of the matrix defining the approximate position of the image (S') on the matrix,a second mode of operation, during which the matrix (120) is first read, by grouping the lines n-by-n (n>p.sub.l), thereafter, line by line in a zone (125) of k lines (k>p.sub.