Each SM sample under scrutiny, itself composed of 2 × 2 pixels, has a so-called working window, centred on it, associated with it. Object detection uses the 5 × 5-samples working window (not shown) for background subtraction and the 3 × 3-samples working window (depicted here for sample i,j = 1,1) for shape assessment of detections. The three-dimensional summed-flux/shape vectors h and v contain, respectively, the along-scan-integrated (AL) and across-scan-integrated (AC) sum of the working-window background-subtracted flux values F_ij, in LSB units (Eq. (1)). The total, background-subtracted flux F in the working window equals F = v₀ + v₁ + v₂ = h₀ + h₁ + h₂.