1. A method of error diffusing an image, the image having a plurality of scan lines each having a plurality of pixels, said method comprising, for each of said pixels, the steps of: applying an error diffusion mask to an output error value of previously processed pixels to determine an input error value for said pixel wherein the error diffusion mask comprises error diffusion coefficients corresponding to all previously error diffused pixels of said image; and determining an output value and an output error value of said pixel, both said output pixel value and said output error value being dependent upon the input error value and an input pixel value of said pixel.