A Bayer-mask is decoded by forming a decoded green array, calculating red green and blue-green color difference signals, deriving a first full-resolution grid of each colour difference signal using a first interpolation filter; deriving a second full-resolution grid of each colour difference signal using a second interpolation filter taking a larger number of colour difference signal inputs than the first; generating a cross-colour weighting signal; and forming a mixed colour difference signal from the first and second full-resolution grids in accordance with the cross-colour weighting signal.