The three channels were first filtered to reduce noise. Typical IKONOS noise is (a) chess patternnoise (common for satellite sensors, increased throughsharpening included in MTFC) and (b) vertical stripes,usually dark but sometimes bright (again typical for linear CCD arrays). A 3x 3 low-pass filter, empirically determined and asymmetric (stronger smoothingin horizontal direction to account for the vertical stripes, was used. The filter coefficients were: