Apparatus for reducing artifacts in error diffused images

DETAILED DESCRIPTION What is claimed is: 1.
Apparatus for a recursive spatial filter which eliminates visible grain patterns from bilevel digital images, said apparatus comprising: means, responsive to pel values that form the incoming image, for producing a pel mask defining an array of pels having columns and rows including an input pel wherein each of said pels in said mask has a corresponding pel value; means, responsive to the values of said pels that form said pel mask, for determining whether said input pel is a part of a grain pattern; means, responsive to the determination that said input pel is part of a grain pattern for interchanging the value of said input pel with that of one of the pels in the outermost columns, whereby said grain patterns are eliminated.
2.
The apparatus in claim 1 wherein said determining means comprises a lookup table for storing a plurality of pre-defined grain patterns such that when the pattern in said mask corresponds to a stored grain pattern, it activates said interchanging means.
3.
The apparatus in claim 2 wherein said array of pels includes feedback pels and said pel mask producing means further comprises: first means for applying at least one of the values of the pels that form a bottom line of said pel mask to a respective address lead of said lookup table; first means for delaying said incoming pel values by a line in order to produce values of pels that will occupy a middle line of said mask; second means for applying the values of at least one of said middle line pel value to respective address leads of said lookup table; second means for delaying each feedback pel value by a line in order to produce values of pels that will occupy a top line of said pel mask; and fourth means for applying the values of at least one of said pels in said top line to a respective access level of said lookup table.
4.
The apparatus in claim 3 wherein said lookup table comprises at least three memory sections, two of said sections for storing the two feedback pel values and the remaining section for storing said filtered pel values