Stack filters for 1-to-N bit image processing in electronic printers

A method of transforming a binary input image B(x,y), represented as a plurality of rasterized binary signals, into a multiple-bit per pixel gray scale:

• image comprising the steps of:
• (a) storing the binary input image B(x,y) in a first memory M(x,y);
• (b) filtering the binary image stored in the first memory M(x,y) to produce a filtered binary image F.sub.1 (x,y);
• (c) storing the filtered binary input image F.sub.1 (x,y) in the first memory M(x,y);
• (d) filtering the binary image stored in the first memory M(x,y) to produce a new filtered binary image F.sub.n (x,y);
• and
• (e) stacking filtered binary image F.sub.1 (x,y) and new filtered binary image F.sub.n (x,y) to produce a gray-scale output image O(x,y), wherein each of a plurality of pixels therein is represented as a two-bit value.

A method for transforming a binary input image B(x,y) into a multiple-bit per pixel gray-scale image comprising the steps of:

• (a) storing the binary input image B(x,y) in a first memory M(x,y);
• (b) filtering the binary image stored in the first memory M(x,y) to produce a filtered binary image F.sub.1 (x,y);
• (c) storing the filtered binary input image F.sub.1 (x,y) in the first memory M(x,y);
• (d) filtering the binary image stored in the first memory M(x,y) to produce a new filtered binary image F.sub.n (x,y);
• (e) stacking filtered binary image F.sub.1 (x,y) and new filtered binary image F.sub.n (x,y) to produce interim image I(x,y), and storing the interim image in a second memory;
• (f) storing the new filtered binary input image F.sub.n (x,y) in the first memory M(x,y);
• (g) filtering the binary image stored in the first memory M(x,y) to produce a new filtered binary image F.sub.n (x,y);
• (h) stacking interim image I(x,y) and new filtered binary image F.sub.n (x,y) to produce a new interim image I(x,y), and storing the interim image in a second memory;
• and
• (i)repeating steps (f) through (h) above for a plurality of times to produce a gray-scale output image O(x,y), wherein each of a plurality of pixels therein is represented as a multiple-bit value.

A digital image filtering apparatus, comprising:

• a first memory for storing a binary input image;
• a first level-slice filter to which the stored binary image may be applied, said first level-slice filter producing a primary binary signal in response to each pixel of the binary image applied thereto to produce a first image slice filter output;
• combination logic for logically combining the first slice filter output and the binary input image to produce a first level slice image;
• a second level-slice flitter to which the first filtered image may be applied, said second level-slice filter producing a secondary binary signal in response to each pixel of the first level-slice image applied thereto to produce a second slice filter output;
• combination logic for logically combining the second slice filter output and the first image slice to produce a second level-slice image;
• and
• stacking logic for logically stacking the second image slice and the first image slice to produce a filtered image that is a multiple-bit per pixel image representing each of a plurality of binary pixels within the binary input image as a two-bit value.

A digital image filtering apparatus, comprising:

• a first memory for storing a binary input image;
• an extensive level-slice filter to which the stored binary image may be applied, said first level-slice filter producing a first binary signal in response to each pixel of the stored binary image applied thereto to produce a first level slice image;
• an anti-extensive level-slice filter to which the stored binary image may be applied, said second level-slice filter producing a second binary signal in response to each pixel of the stored binary image applied thereto to produce a second level slice image;
• and
• stacking logic for logically stacking the second image slice and the first image slice to produce a filtered image that is a multiple-bit per pixel image representing each of a plurality of binary pixels within the binary input image as a two-bit value.

A digital image filtering apparatus for transforming a binary input image represented as a plurality of rasterized binary signals each representing an image pixel, into a multiple-bit per pixel gray scale image, comprising:

• a primary level-slice filter for filtering the binary input image to produce a first filtered binary image;
• a first secondary level-slice filter for filtering the first filtered binary image to produce a second filtered binary image;
• a second secondary level-slice filters for filtering the first filtered binary image to produce a third filtered binary image;
• and
• an adder for adding the first filtered binary image, the second filtered binary image, and the third filtered binary image to produce a gray-scale output image, wherein each of a plurality of pixels therein is represented as a multiple-bit value.

A digital image filtering apparatus for transforming a binary input image represented as a plurality of rasterized binary signals, each representing an image pixel, into a multiple-bit per pixel gray scale image, comprising:

• a first level-slice filter to which the binary input image may be applied, said first level-slice filter producing a first binary signal in response to each pixel of the binary image applied thereto to produce a first image slice;
• a second level-slice filter to which the binary input image may be applied, said second level-slice filter producing a secondary binary signal in response to each pixel of the binary image applied thereto to produce a second image slice;
• and
• means for combining the second image slice and the first image slice to produce a filtered image that is a multiple-bit per pixel image representing each of a plurality of pixels within the input image as a multiple-bit value.