Method for quantization gray level pixel data with extended distribution set

Claim 3

The method as described in claim 1, wherein the weighting of each weighted portion corresponds to: (n+1,l)=0.5; (n-2,l+1)=0.125; (n-1,l+1)=0.125; and (n,l+1)=0.25.

Claim 4

The method as described in claim 1, wherein the preselected plurality of pixels additionally includes pixel (n-3,l+1).

Claim 5

The method as described in claim 3, wherein the weighting of each weighted portion corresponds to: (n+1,l)=0.5; (n-3,l+1)=0.0625; (n-2,l+1)=0.0625; (n-1,l+1)=0.125; (n,l+1)=0.25.

Claim 8

The method as described in claim 5, wherein the weighting of each weighted portion corresponds to: (n+1,l)=0.5; (n-2,l+1)=0.125; (n-1,l+1)=0.125; and (n,l+1)=0.25.

Claim 9

The method as described in claim 5, wherein the preselected plurality of pixels additionally includes pixel (n-3,l+1).

Claim 10

The method as described in claim 7, wherein the weighting of each weighted portion corresponds to: (n+1,l)=0.5; (n-3,l+1)=0.0625; (n-2,l+1)=0.0625; (n-1,l+1)=0.125; (n,l+1)=0.25.

Claim 13

The method as described in claim 9, wherein the weighting of each weighted portion corresponds to: (n+1,l)=0.5; (n-2,l+1)=0.125; (n-1,l+1)=0.125; and (n,l+1)=0.25.

Claim 14

The method as described in claim 9, wherein the preselected plurality of pixels additionally includes pixel (n-3,l+1).

Claim 15

The method as described in claim 11, wherein the weighting of each weighted portion corresponds to: (n+1,l)=0.5; (n-3,l+1)=0.0625; (n-2,l+1)=0.0625;(n-1,l+1)=0,125; (n,l+1)=0.25.

Claim 16

Apparatus for preparing an electronic document for printing at a printer adapted to printing n level spots for each pixel, the steps comprising: a document input receiving document images defined in terms of digital electronic input signals, each signal having a magnitude selected from one of m levels (where m is greater than n) and corresponding to a pixel and describing density of the document at position n in a scan line l (n,l); a summing circuit, adding to each input signal an error signal resulting from quantization of previous signals, if any, to derive a modified input signal; a comparator, operatively connected to said document input to receive the modified input signals and to a source of threshold signals, and producing an output response selected from one of the n level spots upon comparing each modified input signal with a threshold signal; a difference circuit receiving as inputs the output response and the modified input signals and deriving an digital electronic error term signal representing the difference in density between the output response and the modified input signal; a first error term buffer and a corresponding shift register operatively connected to said difference circuit, receiving an error term from quantization of signal (n-1,l) therefrom and shifting the error term for addition of a weighted portion thereof at said summing circuit to input signal n in scan line l (n,l); a line buffer operatively connected to the first error term buffer, storing a line of error term signals corresponding to signals in scan line l-1; at least second, third and fourth error term buffers, each having a corresponding shift register, and operatively connected to said line buffer, to receive error terms from the quantization of signals at positions (n,l-1), (n+1,l-1), (n+2,l-1) each shift register shifting the error term for addition of a weighted portion thereof at said summing circuit to input signal n in scan line l (n,l).

Claim 17

Apparatus for preparing an electronic document for printing at a printer adapted to printing n level spots for each pixel, the steps comprising: a document input receiving document images defined in terms of digital electronic input signals, each signal having a magnitude selected from one of m levels (where m is greater than n) and corresponding to a pixel and describing density of the document at position n in a scan line l (n,l); a summing circuit, adding to each input signal an error signal resulting from quantization of previous signals, if any, to derive a modified input signal; a comparator, operatively connected to said document input to receive the modified input signals and to a source of threshold signals, and producing an output response selected from one of the n level spots upon comparing each modified input signal with a threshold signal; a difference circuit receiving as inputs the output response and the modified input signals and deriving an digital electronic error term signal representing the difference in density between the output response and the modified input signal; a first error term buffer and a corresponding shift register operatively connected to said difference circuit, receiving an error term from quantization of signal (n-1,l) therefrom and shifting the error term for addition of a weighted portion thereof at said summing circuit to input signal n in scan line l (n,l); a line buffer operatively connected to the first error term buffer, storing a line of error term signals corresponding to signals in scan line l-1; at least second, third and fourth error term buffers, each having a corresponding shift register, and operatively connected to said line buffer, to receive error terms from the quantization of signals at positions (n,l-1), (n+1,l-1), (n+2,l-1) each shift register shifting the error term for addition of a weighted portion thereof at said summing circuit to input signal n in scan line l (n,l).

Claim 18

The apparatus as described in claim 13, wherein the weighted portions of the error term from positions (n,l-1), (n+1,l-1), (n+2,l-1) corresponds to: (n-1,l)=0.5; (n+2,l-1)=0.125; (n+1,l-1)=0.125; and (n,l-1)=0.25.

Claim 19

The apparatus as described in claim 13, including a fifth error term buffer and corresponding shift register, and operatively connected to said line buffer, to receive error terms from the quantization of a signal at position (n+3, l-1), each shift register shifting the error term for addition of a weighted portion thereof at said summing circuit to input signal n in scan line l (n,l).

Claim 20

The apparatus as described in claim 15, wherein the weighting of each weighted portion corresponds to: (n-1,l)=0.5; (n+3,l-1)=0.0625; (n+2,l-1)=0.0625; (n+1,l-1)=0.125; (n,l-1)=0.25.