A halftone raster image suitable for rendering a continuous-tone image includes a plurality of spiral dots. The spiral dots include image pixels arranged as a first arc or as a plurality of arcs which together represent a first spiral, and non-image pixels arranged as a second arc or as a plurality of arcs which together represent a second spiral. The spiral dots enable a controlled spreading of the ink within the dot, resulting in a higher image quality, ink saving, and faster drying.