The present disclosure provides a method for image dithering. The method includes providing a polygon related to an integrated circuit (IC) layout design in a graphic database system (GDS) grid; converting the polygon to an intensity map in the GDS grid, the intensity map including a group of partial pixels and a group of full pixels; performing a first quantization process to a partial pixel to determine a first error; applying the first error to one or more full pixels; performing a second quantization process to a full pixel to determine a second error; and distributing the second error to one or more full pixels. The partial pixels correspond to pixels partially covered by the polygon, and the full pixels correspond to pixels fully covered by the polygon.