Method combining error diffusion and traditional halftoning with arbitrary screen orientation

Claim 1

A method of reducing coarse quantization artifacts in an image comprising the steps of: partitioning the image stored in memory into disjointed blocks, each block comprising a plurality of pixels, each pixel having a threshold level; thresholding the levels to at least two representative levels; determining a first threshold level for each block representative of a maximum threshold level that produces one of said representative levels and a second threshold level for each block representative of a minimum threshold level that produces a second one of said two representative levels; further determining a first number of pixels in each of said blocks having said first threshold level and a second number of pixels having said second threshold level; comparing said first threshold level of said block to said second threshold level of said block; measuring levels of data input to each of the blocks provided said compared second threshold level is greater than said compared first threshold level; calculating an average value and a critical local error of each of the blocks provided said measured input levels are homogeneous; determining which of the blocks are critical blocks using said calculated critical local errors; multiplying said local critical errors by said first number of pixels; adding results of said multiplication to propagated errors to determine a total error for each block; determining whether a total error is <-0.5/L or ≦0.5/L for each critical block; first changing pixels in one of said critical blocks having said second threshold level provided said total error of said critical block is greater than 0; reducing said total error of said critical block by 1/L until said total error is less than 0.5/L where L is the size of a halftone cell; second changing pixels in one of said critical blocks having said first threshold level provided said total error of said critical block is less than 0; increasing said total error of said critical block having said changed second pixels by 1/L until said total error is greater than or equal to -0.5/L; and diffusing each of said reduced or increased total errors of each of said critical blocks or total errors of unchanged critical blocks and non-critical blocks to at least one neighboring block.

Claim 2

A method of reducing coarse quantization artifacts in an image comprising the steps of: partitioning the image stored in memory into disjointed blocks, each block comprising a plurality of pixels, each pixel having a threshold level; thresholding the levels to at least two representative levels; determining a first threshold level for each block representative of a maximum threshold level that produces one of said representative levels and a second threshold level for each block representative of a minimum threshold level that produces a second one of said two representative levels; further determining a first number of pixels in each of said blocks having said first threshold level and a second number of pixels having said second threshold level; comparing said first threshold level of said block to said second threshold level of said block; measuring levels of data input to each of the blocks provided said compared second threshold level is greater than said compared first threshold level; calculating an average value and a critical local error of each of the blocks provided said measured input levels are homogeneous; determining which of the blocks are critical blocks using said calculated critical local errors; multiplying said local critical errors by said first number of pixels; adding results of said multiplication to propagated errors to determine a total error for each block; determining whether a total error is <-0.5/L or ≦0.5/L for each critical block; first changing pixels in one of said critical blocks having said second threshold level provided said total error of said critical block is greater than 0; reducing said total error of said critical block by 1/L until said total error is less than 0.5/L where L is the size of a halftone cell; second changing pixels in one of said critical blocks having said first threshold level provided said total error of said critical block is less than 0; increasing said total error of said critical block having said changed second pixels by 1/L until said total error is greater than or equal to -0.5/L; and diffusing each of said reduced or increased total errors of each of said critical blocks or total errors of unchanged critical blocks and non-critical blocks to at least one neighboring block.

Claim 9

A method of reducing coarse quantization artifacts in an image comprising the steps of: partitioning the image stored in memory into disjointed blocks, each block comprising a plurality of pixels, each pixel having a threshold level; thresholding the levels to at least two representative levels; determining a first threshold level for each block representative of a maximum threshold level that produces one of said representative levels and a second threshold level for each block representative of a minimum threshold level that produces a second one of said two representative levels; further determining a first number of pixels in each of said blocks having said first threshold level and a second number of pixels having said second threshold level; comparing said first threshold level of said block to said second threshold level of said block; measuring levels of data input to each of the blocks provided said compared second threshold level is greater than said compared first threshold level; calculating an average value and a critical local error of each of the blocks provided said measured input levels are homogeneous; determining which of the blocks are critical blocks using said calculated critical local errors; multiplying said local critical errors by said first number of pixels; adding results of said multiplication to propagated errors to determine a total error for each block; determining whether a total error is <-0.5/L or ≦0.5/L for each critical block where L is the size of a halftone cell; and reducing quantization artifacts in a critical block having a total error ≦0.5/L or <-0.5/L using said critical local error of said critical block.

Claim 10

A method of reducing coarse quantization artifacts in an image comprising the steps of: partitioning the image stored in memory into disjointed blocks, each block comprising a plurality of pixels, each pixel having a threshold level; thresholding the levels to at least two representative levels; determining a first threshold level for each block representative of a maximum threshold level that produces one of said representative levels and a second threshold level for each block representative of a minimum threshold level that produces a second one of said two representative levels; further determining a first number of pixels in each of said blocks having said first threshold level and a second number of pixels having said second threshold level; comparing said first threshold level of said block to said second threshold level of said block; measuring levels of data input to each of the blocks provided said compared second threshold level is greater than said compared first threshold level; calculating an average value and a critical local error of each of the blocks provided said measured input levels are homogeneous; determining which of the blocks are critical blocks using said calculated critical local errors; multiplying said local critical errors by said first number of pixels; adding results of said multiplication to propagated errors to determine a total error for each block; determining whether a total error is <-0.5/L or ≦0.5/L for each critical block where L is the size of a halftone cell; and reducing quantization artifacts in a critical block having a total error ≦0.5/L or <-0.5/L using said critical local error of said critical block.