Error diffusion using next scanline error impulse response

An apparatus for halftoning an image is disclosed. The apparatus comprises means for determining an output value of a current pixel on a current scanline using a sum of an input value for the current pixel and a neighborhood error value at the current pixel, means for determining an error at the current pixel as the difference between (i) the sum of the input value for the current pixel and the neighborhood error value at the current pixel, and (ii) the output value of the current pixel; and means for adding a proportion of the error at the current pixel to neighborhood error values at as yet unprocessed pixels of a subsequent scanline in accordance with a next scanline error impulse response; wherein said next scanline error impulse response approximates a function which spreads with self-convolution in proportion to a degree of self-convolution.