Bit mask generation system and printer drivers and printing methods incorporating bit masks generated utilising same

摘要

A printing system is disclosed where a multi level pixel image (200) is converted into a half tone image (300) utilising a set of bit mask arrays (350-0 to 350-255) stored within a memory (310). The value of a multi level pixel is used to select one of the stored bit mask arrays. The co-ordinates of the multi level pixel in an image are then used to identify an entry from within the selected bit mask array. The identified entry is then used to set the value of the corresponding pixel in the half tone image. In order to reduce the appearance of contouring at the boundaries of adjacent portions of an image having similar grey levels, the stored bit mask arrays (350-0 to 350-255) are such that the majority of entries in the bit mask arrays for successive grey levels are identical. In addition to reducing contouring problems, the similarity of significant portions of bit mask arrays for successive grey levels make the bit mask arrays suitable for compression.