1. A system for improving an appearance of a raster image comprising glyph shapes, comprising: a pair of glyph shapes, that each comprise differentiated two-dimensional machine readable data of relatively uniform appearance, each assigned to a different bit value; an encoder to encode digital data from an input source into a bitmap image space by representing a bit value for each item of the digital data as the glyph shape corresponding to that bit value; and a raster generator to generate a raster image of the encoded glyph shapes from the bitmap image space.