1. A method for reducing a resolution of a digital colour image ( 100 ) where the digital colour image comprises pixels ( 101 ) arranged in a colour mask ( 102 ) of at least three different colours, the pixels comprise first pixels (R), second pixels (G), third pixels (g) and fourth pixels (B), the method comprising: recording a digital colour image using the colour mask ( 102 ); selecting n×n first pixels (R) outlining a first square (SR), and using values of these selected n×n pixels for generating a value of a first macro pixel ( 202 , RR); selecting n×n second pixels (G) outlining a second square (SG) being rotated 45 degrees and shifted horizontally relative to the first square (SR), and using values of these selected n×n pixels for generating a value of a second macro pixel ( 202 , GG); selecting n×n third pixels (g) outlining a third square (Sg) being rotated 45 degrees and shifted vertically relative to the first square (SR), and using values of the n×n pixels for generating a value of a third macro pixel ( 202 , gg),where each of the first, second and third macro pixels has an optical centre ( 201 , CR, CG, Cg) determined by the relative positions of the pixels used to generate the value of the macro pixel ( 202 ), wherein the pixels used to generate values of the first, second and third macro pixels are selected to position the optical centres ( 201 ) of each of the first, second and third macro pixels ( 202 ) at identical positions within each of the first, second and third macro pixels, so that these optical centres form a uniform grid (WG); and selecting M pixels from n×n fourth pixels (B) outlining a fourth square (SB) oriented identically to and shifted diagonally relative to the first square (SR), M being greater than zero and less than or equal to n×n, and using values of the M pixels for generating a value of a fourth macro pixel ( 202 ,BB).