Halftoning with gradient-based selection of dither matrices

Claim 3

A method according to claim 1, wherein the plural dither matrices are reciprocally compatible.

Claim 4

A method according to claim 2, wherein the plural dither matrices all originate from a common basic dither matrix, have a common relative phase, and include at least one supercell dither matrix and a basic dither matrix such that normalized relative inter-tile differences in the supercell dither matrices are smaller than the normalized inter-pixel differences in the basic dither matrix.

Claim 5

A method according to claim 1, wherein said plural dither matrices are comprised by first and second dither matrices, and wherein the tonality gradient is calculated by comparing the gray scale image data for the target pixel with gray scale image data for all immediately adjacent pixels, and wherein the first dither matrix is selected in a case where all gray scale data is the same and the second dither matrix is selected if any of the gray scale image data is different.

Claim 6

A method according to claim 1, wherein said plural dither matrices are comprised by first, second and third dither matrices, wherein the local tonality gradient is calculated by identifying the presence of a large gradient, no gradient, and at least one intermediate gradient, and wherein the first dither matrix is selected in a case where a large gradient is identified, the second dither matrix is selected in a case where no gradient is identified, and the third dither matrix is selected in a case where an intermediate dither matrix is identified.

Claim 7

A halftone printing method for printing a halftone image corresponding to a gray scale image, comprising the steps of: accepting a selection to halftone according to error diffusion or according to dithering; halftoning by error diffusion in a case where a selection to halftone according to error diffusion is selected; halftoning by dithering in a case where a selection to halftone according to dithering is selected; wherein in a case where halftoning according to error diffusion is selected (a) a local tonality gradient of gray scale image data for a target pixel is calculated based on a comparison between at least the gray scale image data for the target pixel and gray scale image data for a pixel adjacent the target pixel, (b) one dither matrix is selected from among plural dither matrices based on the calculated tonality gradient, each of the plural dither matrices containing threshold values which differ from others of the plural dither matrices, and (c) the gray scale image data is thresholded for the target pixel using the selected dither matrix so as to obtain halftone image data for the target pixel.

Claim 8

A halftone printing method for printing a halftone image corresponding to a gray scale image, comprising the steps of: accepting a selection to halftone according to error diffusion or according to dithering; halftoning by error diffusion in a case where a selection to halftone according to error diffusion is selected; halftoning by dithering in a case where a selection to halftone according to dithering is selected; wherein in a case where halftoning according to error diffusion is selected (a) a local tonality gradient of gray scale image data for a target pixel is calculated based on a comparison between at least the gray scale image data for the target pixel and gray scale image data for a pixel adjacent the target pixel, (b) one dither matrix is selected from among plural dither matrices based on the calculated tonality gradient, each of the plural dither matrices containing threshold values which differ from others of the plural dither matrices, and (c) the gray scale image data is thresholded for the target pixel using the selected dither matrix so as to obtain halftone image data for the target pixel.

Claim 9

A method according to claim 6, wherein the plural dither matrices are reciprocally compatible.

Claim 10

A method according to claim 7, wherein the plural dither matrices all originate from a common basic dither matrix, have a common relative phase, and include at least one supercell dither matrix and a basic dither matrix such that normalized relative inter-tile differences in the supercell dither matrices are smaller than the normalized inter-pixel differences in the basic dither matrix.

Claim 11

A method according to claim 6, wherein said plural dither matrices are comprised by first and second dither matrices, and wherein the tonality gradient is calculated by comparing the gray scale image data for the target pixel with gray scale image data for all immediately adjacent pixels, and wherein the first dither matrix is selected in a case where all gray scale data is the same and the second dither matrix is selected if any of the gray scale image data is different.

Claim 12

A method according to claim 6, wherein said plural dither matrices are comprised by first, second and third dither matrices, wherein the local tonality gradient is calculated by identifying the presence of a large gradient, no gradient, and at least one intermediate gradient, and wherein the first dither matrix is selected in a case where a large gradient is identified, the second dither matrix is selected in a case where no gradient is identified, and the third dither matrix is selected in a case where an intermediate dither matrix is identified.

Claim 15

An apparatus according to claim 11, wherein the plural dither matrices are reciprocally compatible.

Claim 16

An apparatus according to claim 12, wherein the plural dither matrices all originate from a common basic dither matrix, have a common relative phase, and include at least one supercell dither matrix and a basic dither matrix such that normalized relative inter-tile differences in the supercell dither matrices are smaller than the normalized inter-pixel differences in the basic dither matrix.

Claim 17

An apparatus according to claim 11, wherein said plural dither matrices are comprised by first and second dither matrices, and wherein the tonality gradient is calculated by comparing the gray scale image data for the target pixel with gray scale image data for all immediately adjacent pixels, and wherein the first dither matrix is selected in a case where all gray scale data is the same and the second dither matrix is selected if any of the gray scale image data is different.

Claim 18

An apparatus according to claim 11, wherein said plural dither matrices are comprised by first, second and third dither matrices, wherein the local tonality gradient is calculated by identifying the presence of a large gradient, no gradient, and at least one intermediate gradient, and wherein the first dither matrix is selected in a case where a large gradient is identified, the second dither matrix is selected in a case where no gradient is identified, and the third dither matrix is selected in a case where an intermediate dither matrix is identified.

Claim 19

A halftone printing apparatus for printing a halftone image corresponding to a gray scale image, comprising: accepting means for accepting a selection to halftone according to error diffusion or according to dithering; halftoning means for halftoning by error diffusion in a case where a selection to halftone according to error diffusion is selected; halftoning means for halftoning by dithering in a case where a selection to halftone according to dithering is selected; wherein, in a case where halftoning according to dithering is selected, said process steps include steps to (a) calculate a local tonality gradient of gray scale image data for a target pixel, the tonality gradient being calculated based on a comparison between at least the gray scale image data for the target pixel and gray scale image data for a pixel adjacent the target pixel, (b) select one dither matrix from among plural dither matrices based on the calculated tonality gradient, each of the plural dither matrices containing threshold values which differ from others of the plural dither matrices, and (c) threshold the gray scale image data for the target pixel using the selected dither matrix so as to obtain halftone image data for the target pixel.

Claim 20

A halftone printing apparatus for printing a halftone image corresponding to a gray scale image, comprising: accepting means for accepting a selection to halftone according to error diffusion or according to dithering; halftoning means for halftoning by error diffusion in a case where a selection to halftone according to error diffusion is selected; halftoning means for halftoning by dithering in a case where a selection to halftone according to dithering is selected; wherein, in a case where halftoning according to dithering is selected, said process steps include steps to (a) calculate a local tonality gradient of gray scale image data for a target pixel, the tonality gradient being calculated based on a comparison between at least the gray scale image data for the target pixel and gray scale image data for a pixel adjacent the target pixel, (b) select one dither matrix from among plural dither matrices based on the calculated tonality gradient, each of the plural dither matrices containing threshold values which differ from others of the plural dither matrices, and (c) threshold the gray scale image data for the target pixel using the selected dither matrix so as to obtain halftone image data for the target pixel.

Claim 21

An apparatus according to claim 16, wherein the plural dither matrices are reciprocally compatible.

Claim 22

An apparatus according to claim 17, wherein the plural dither matrices all originate from a common basic dither matrix, have a common relative phase, and include at least one supercell dither matrix and a basic dither matrix such that normalized relative inter-tile differences in the supercell dither matrices are smaller than the normalized inter-pixel differences in the basic dither matrix.

Claim 23

An apparatus according to claim 16, wherein said plural dither matrices are comprised by first and second dither matrices, and wherein the tonality gradient is calculated by comparing the gray scale image data for the target pixel with gray scale image data for all immediately adjacent pixels, and wherein the first dither matrix is selected in a case where all gray scale data is the same and the second dither matrix is selected if any of the gray scale image data is different.

Claim 24

An apparatus according to claim 16, wherein said plural dither matrices are comprised by first, second and third dither matrices, wherein the local tonality gradient is calculated by identifying the presence of a large gradient, no gradient, and at least one intermediate gradient, and wherein the first dither matrix is selected in a case where a large gradient is identified, the second dither matrix is selected in a case where no gradient is identified, and the third dither matrix is selected in a case where an intermediate dither matrix is identified.

Claim 25

Computer-executable process steps stored on a computer readable medium, said process steps for obtaining halftone image data from corresponding gray scale image data, the gray scale image data being representative of pixels in an image and arbitrarily including values representative of both highlights and midtones for the image, said process steps comprising: a calculating step to calculate a local tonality gradient of gray scale image data for a target pixel, the tonality gradient being calculated based on a comparison between at least the gray scale image data for the target pixel and gray scale image data for a pixel adjacent the target pixel; a selecting step to select one dither matrix from among plural dither matrices based on the calculated tonality gradient, each of the plural dither matrices containing threshold values which differ from others of the plural dither matrices; and a thresholding step to threshold the gray scale image data for the target pixel using the selected dither matrix so as to obtain halftone image data for the target pixel.

Claim 26

Computer-executable process steps stored on a computer readable medium, said process steps for obtaining halftone image data from corresponding gray scale image data, the gray scale image data being representative of pixels in an image and arbitrarily including values representative of both highlights and midtones for the image, said process steps comprising: a calculating step to calculate a local tonality gradient of gray scale image data for a target pixel, the tonality gradient being calculated based on a comparison between at least the gray scale image data for the target pixel and gray scale image data for a pixel adjacent the target pixel; a selecting step to select one dither matrix from among plural dither matrices based on the calculated tonality gradient, each of the plural dither matrices containing threshold values which differ from others of the plural dither matrices; and a thresholding step to threshold the gray scale image data for the target pixel using the selected dither matrix so as to obtain halftone image data for the target pixel.

Claim 27

Computer-executable process steps according to claim 21, wherein the plural dither matrices are reciprocally compatible.

Claim 28

Computer-executable process steps according to claim 22, wherein the plural dither matrices all originate from a common basic dither matrix, have a common relative phase, and include at least one supercell dither matrix and a basic dither matrix such that normalized relative inter-tile differences in the supercell dither matrices are smaller than the normalized inter-pixel differences in the basic dither matrix.

Claim 29

Computer-executable process steps according to claim 21, wherein said plural dither matrices are comprised by first and second dither matrices, and wherein the tonality gradient is calculated by comparing the gray scale image data for the target pixel with gray scale image data for all immediately adjacent pixels, and wherein the first dither matrix is selected in a case where all gray scale data is the same and the second dither matrix is selected if any of the gray scale image data is different.

Claim 30

Computer-executable process steps according to claim 21, wherein said plural dither matrices are comprised by first, second and third dither matrices, wherein the local tonality gradient is calculated by identifying the presence of a large gradient, no gradient, and at least one intermediate gradient, and wherein the first dither matrix is selected in a case where a large gradient is identified, the second dither matrix is selected in a case where no gradient is identified, and the third dither matrix is selected in a case where an intermediate dither matrix is identified.