Method and apparatus for generating halftone images with adjusted screen angles

Claim 1

An apparatus for generating a dot signal for a plurality of color separations to record a halftone image of each color separation, comprising: area dividing means for dividing a whole image area into a plurality of image areas; screen angle assigning means for assigning a set of screen angles for said plurality of color separations with respect to each of said plurality of image areas; a first memory for storing a plurality of color-separated image signals for said plurality of color separations, said plurality of color-separated image signals representing a color image in said whole image area; a second memory for storing a plurality of screen pattern data for said plurality of color separations; selection means for selecting one of said plurality of screen pattern data for each color separation in each of said plurality of image areas according to said assigned set of screen angles assigned to each of said plurality of image areas; and a dot signal generator for comparing the selected screen pattern data with the color-separated image data for each separation, to thereby generate a dot signal for recording a halftone image of each color separation, wherein said plurality of color separations include four color separations for yellow, magenta, cyan and black inks and said apparatus, further comprising: a third memory for storing reference data assigned to an overlapping area, the overlapping area being formed between first and second image areas so that a density of each of four color separations of said overlapping area is equal to one of the first and second image areas, said reference data indicating, with respect to each of the magenta and cyan separations, which one of the two screen angles for the first and second image areas is used as a screen angle of the overlapping area.

Claim 2

An apparatus for generating a dot signal for a plurality of color separations to record a halftone image of each color separation, comprising: area dividing means for dividing a whole image area into a plurality of image areas; screen angle assigning means for assigning a set of screen angles for said plurality of color separations with respect to each of said plurality of image areas; a first memory for storing a plurality of color-separated image signals for said plurality of color separations, said plurality of color-separated image signals representing a color image in said whole image area; a second memory for storing a plurality of screen pattern data for said plurality of color separations; selection means for selecting one of said plurality of screen pattern data for each color separation in each of said plurality of image areas according to said assigned set of screen angles assigned to each of said plurality of image areas; and a dot signal generator for comparing the selected screen pattern data with the color-separated image data for each separation, to thereby generate a dot signal for recording a halftone image of each color separation, wherein said plurality of color separations include four color separations for yellow, magenta, cyan and black inks and said apparatus, further comprising: a third memory for storing reference data assigned to an overlapping area, the overlapping area being formed between first and second image areas so that a density of each of four color separations of said overlapping area is equal to one of the first and second image areas, said reference data indicating, with respect to each of the magenta and cyan separations, which one of the two screen angles for the first and second image areas is used as a screen angle of the overlapping area.

Claim 3

An apparatus for generating a dot signal for a plurality of color separations to record a halftone image of each color separation, comprising: area dividing means for dividing a whole image area into a plurality of image areas; screen angle assigning means for assigning a set of screen angles for said plurality of color separations with respect to each of said plurality of image areas; a first memory for storing a plurality of color-separated image signals for said plurality of color separations, said plurality of color-separated image signals representing a color image in said whole image area; a second memory for storing a plurality of screen pattern data for said plurality of color separations; selection means for selecting one of said plurality of screen pattern data for each color separation in each of said plurality of image areas according to said assigned set of screen angle assigned to each of said plurality of image areas; and a dot signal generator for comparing the selected screen pattern data with the color-separated image data for each separation, to thereby generate a dot signal for recording a halftone image of each color separation, wherein said plurality of color separations include four color separations for yellow, magenta, cyan and black inks and said apparatus, further comprising: a third memory for storing mode data assigned to each of the plurality of image areas, the mode data representing a first mode where screen angles of the magenta and cyan separations are set at predetermined standard values, and a second mode where the screen angles of the magenta and cyan separations are exchanged each other from the predetermined standard values; and screen angle data generating means for producing the screen angle data of the magenta and cyan separations according to the mode data.

Claim 4

An apparatus for generating a dot signal for a plurality of color separations to record a halftone image of each color separation, comprising: area dividing means for dividing a whole image area into a plurality of image areas; screen angle assigning means for assigning a set of screen angles for said plurality of color separations with respect to each of said plurality of image areas; a first memory for storing a plurality of color-separated image signals for said plurality of color separations, said plurality of color-separated image signals representing a color image in said whole image area; a second memory for storing a plurality of screen pattern data for said plurality of color separations; selection means for selecting one of said plurality of screen pattern data for each color separation in each of said plurality of image areas according to said assigned set of screen angle assigned to each of said plurality of image areas; and a dot signal generator for comparing the selected screen pattern data with the color-separated image data for each separation, to thereby generate a dot signal for recording a halftone image of each color separation, wherein said plurality of color separations include four color separations for yellow, magenta, cyan and black inks and said apparatus, further comprising: a third memory for storing mode data assigned to each of the plurality of image areas, the mode data representing a first mode where screen angles of the magenta and cyan separations are set at predetermined standard values, and a second mode where the screen angles of the magenta and cyan separations are exchanged each other from the predetermined standard values; and screen angle data generating means for producing the screen angle data of the magenta and cyan separations according to the mode data.

Claim 8

An apparatus for generating a dot signal for a plurality of color separations to record a halftone image of each color separation, comprising: area dividing means for dividing a whole image area into a plurality of image areas; screen angle assigning means for assigning a set of screen angles for said plurality of color separations with respect to each of said plurality of image areas; a first memory for storing a plurality of color-separated image signals for said plurality of color separations, said plurality of color-separated image signals representing a color image in said whole image area; a second memory for storing a plurality of screen pattern data for said plurality of color separations; selection means for selecting one of said plurality of screen pattern data for each color separation in each of said plurality of image areas according to said assigned set of screen angles assigned to each of said plurality of image areas; and a dot signal generator for comparing the selected screen pattern data with the color-separated image data for each separation, to thereby generate a dot signal for recording a halftone image of each color separation, wherein said plurality of color separations include four color separations for yellow, magenta, cyan and black inks and said apparatus, further comprising: a third memory for storing mode data assigned to each of the plurality of image areas, the mode data representing a first mode where screen angles of the four color separations are set at predetermined standard values, and a second mode where the screen angles of the four color separations are adjusted from the predetermined standard values; and screen angle data generating means for producing the screen angle data representing screen angles θ(Y), θ(M), θ(C), and θ(K) for yellow, magenta, cyan, and black, respectively, according to the following Table A with respect to pixels to which the mode data indicating the second mode is assigned: TABLE A ______________________________________ COLOR RELATIONS SEPARATION OF DOT % SCREEN ANGLES NEITHER D(Y), D(M), θ θ θ θ 100%/0% D(C), D(K) (Y) (M) (C) (K) ______________________________________ Y N/A 45 -- -- -- M N/A -- 45 -- -- C N/A -- -- 45 -- K N/A -- -- -- 45 Y and M N/A 0 45 -- -- Y and C N/A 0 -- 45 -- Y and K N/A 0 -- -- 45 M and C D(M) > D(C) -- 45 0 -- M and C D(M) ≦ D(C) -- 0 45 -- M and K D(M) > D(K) -- 45 -- 0 M and K D(M) ≦ D(K) -- 0 -- 45 C and K D(C) > D(K) -- -- 45 0 C and K D(C) ≦ D(K) -- -- 0 45 Y, M and C D(M) > D(C) 75 45 15 -- Y, M and C D(M) ≦ D(C) 75 15 45 -- Y, M and K D(M) > D(K) 75 45 -- 15 Y, M and K D(M) ≦ D(K) 75 15 -- 45 Y, C and K D(C) > D(K) 75 -- 45 15 Y, C and K D(C) ≦ D(K) 75 -- 15 45 M, C and K D(M) > D(C) & -- 45 15 75 D(M) > D(K) M, C and k D(C) ≧ D(M) & -- 15 45 75 D(C) > D(K) M, C and k D(K) ≧ D(M) & -- 15 75 45 D(K) ≧ D(C) Y, M, C and K D(M) > D(C) & 0 45 15 75 D(M) > D(K) Y, M, C and k D(C) ≧ D(M) & 0 15 45 75 D(C) > D(K) Y, M, C and k D(K) ≧ D(M) & 0 15 75 45 D(K) ≧ D(C) ______________________________________ where D(Y), D(M), D(C), and D(K) denote dot percentages of yellow, magenta, cyan, and black, respectively, "N/A" means that there are no conditions for the relations among the dot percentages D(Y), D(M), D(C), and D(K).

Claim 9

An apparatus for generating a dot signal for a plurality of color separations to record a halftone image of each color separation, comprising: area dividing means for dividing a whole image area into a plurality of image areas; screen angle assigning means for assigning a set of screen angles for said plurality of color separations with respect to each of said plurality of image areas; a first memory for storing a plurality of color-separated image signals for said plurality of color separations, said plurality of color-separated image signals representing a color image in said whole image area; a second memory for storing a plurality of screen pattern data for said plurality of color separations; selection means for selecting one of said plurality of screen pattern data for each color separation in each of said plurality of image areas according to said assigned set of screen angles assigned to each of said plurality of image areas; and a dot signal generator for comparing the selected screen pattern data with the color-separated image data for each separation, to thereby generate a dot signal for recording a halftone image of each color separation, wherein said plurality of color separations include four color separations for yellow, magenta, cyan and black inks and said apparatus, further comprising: a third memory for storing mode data assigned to each of the plurality of image areas, the mode data representing a first mode where screen angles of the four color separations are set at predetermined standard values, and a second mode where the screen angles of the four color separations are adjusted from the predetermined standard values; and screen angle data generating means for producing the screen angle data representing screen angles θ(Y), θ(M), θ(C), and θ(K) for yellow, magenta, cyan, and black, respectively, according to the following Table A with respect to pixels to which the mode data indicating the second mode is assigned: TABLE A ______________________________________ COLOR RELATIONS SEPARATION OF DOT % SCREEN ANGLES NEITHER D(Y), D(M), θ θ θ θ 100%/0% D(C), D(K) (Y) (M) (C) (K) ______________________________________ Y N/A 45 -- -- -- M N/A -- 45 -- -- C N/A -- -- 45 -- K N/A -- -- -- 45 Y and M N/A 0 45 -- -- Y and C N/A 0 -- 45 -- Y and K N/A 0 -- -- 45 M and C D(M) > D(C) -- 45 0 -- M and C D(M) ≦ D(C) -- 0 45 -- M and K D(M) > D(K) -- 45 -- 0 M and K D(M) ≦ D(K) -- 0 -- 45 C and K D(C) > D(K) -- -- 45 0 C and K D(C) ≦ D(K) -- -- 0 45 Y, M and C D(M) > D(C) 75 45 15 -- Y, M and C D(M) ≦ D(C) 75 15 45 -- Y, M and K D(M) > D(K) 75 45 -- 15 Y, M and K D(M) ≦ D(K) 75 15 -- 45 Y, C and K D(C) > D(K) 75 -- 45 15 Y, C and K D(C) ≦ D(K) 75 -- 15 45 M, C and K D(M) > D(C) & -- 45 15 75 D(M) > D(K) M, C and k D(C) ≧ D(M) & -- 15 45 75 D(C) > D(K) M, C and k D(K) ≧ D(M) & -- 15 75 45 D(K) ≧ D(C) Y, M, C and K D(M) > D(C) & 0 45 15 75 D(M) > D(K) Y, M, C and k D(C) ≧ D(M) & 0 15 45 75 D(C) > D(K) Y, M, C and k D(K) ≧ D(M) & 0 15 75 45 D(K) ≧ D(C) ______________________________________ where D(Y), D(M), D(C), and D(K) denote dot percentages of yellow, magenta, cyan, and black, respectively, "N/A" means that there are no conditions for the relations among the dot percentages D(Y), D(M), D(C), and D(K).

Claim 10

An apparatus for generating a dot signal for a plurality of color separations to record a halftone image of each color separation, comprising: area dividing means for dividing a whole image area into a plurality of image areas; screen angle assigning means for assigning a set of screen angles for said plurality of color separations with respect to each of said plurality of image areas; a first memory for storing a plurality of color-separated image signals for said plurality of color separations, said plurality of color-separated image signals representing a color image in said whole image area; a second memory for storing a plurality of screen pattern data for said plurality of color separations; selection means for selecting one of said plurality of screen pattern data for each color separation in each of said plurality of image areas according to said assigned set of screen angles assigned to each of said plurality of image areas; and a dot signal generator for comparing the selected screen pattern data with the color-separated image data for each separation, to thereby generate a dot signal for recording a halftone image of each color separation, wherein said plurality of color separations include four color separations for yellow, magenta, cyan and black inks and said apparatus, further comprising: a third memory for storing mode data assigned to each of the plurality of image areas, the mode data representing a first mode where screen angles of the four color separations are set at predetermined standard values, and a second mode when the screen angles of the four color separations are adjusted from the predetermined standard values; and screen angle data generating means for producing the screen angle data representing screen angles 0(Y), 0(M), 0(C), and 0(K) for yellow, magenta, cyan and black, respectively, according to the following Table B with respect to pixels to which the mode data indicating the second mode is assigned: TABLE B ______________________________________ COLOR RELATIONS SEPARATION OF DOT % SCREEN ANGLES NEITHER D(Y), D(M), θ θ θ θ 100%/0% D(C), D(K) (Y) (M) (C) (K) ______________________________________ Y N/A 45 -- -- -- M N/A -- 45 -- -- C N/A -- -- 45 -- K N/A -- -- -- 45 Y and M N/A 0 45 -- -- Y and C N/A 0 -- 45 -- Y and K N/A 0 -- -- 45 M and C D(M) > D(C) -- 45 15 -- M and C D(M) ≦ D(C) -- 15 45 -- M and K D(M) > D(K) -- 45 -- 75 M and K D(M) ≦ D(K) -- 15 -- 45 C and K D(C) > D(K) -- -- 45 75 C and K D(C) ≦ D(K) -- -- 15 45 Y, M and C D(M) > D(C) 15/75 45 0 -- Y, M and C D(M) ≦ D(C) 15/75 0 45 -- Y, M and K D(M) > D(K) 15/75 45 -- 0 Y, M and K D(M) ≦ D(K) 15/75 0 -- 45 Y, C and K D(C) > D(K) 15/75 -- 45 0 Y, C and K D(C) ≦ D(K) 15/75 -- 0 45 M, C and K D(M) > D(C) & -- 45 15 75 D(M) > D(K) M, C and k D(C) ≧ D(M) & -- 15 45 75 D(C) > D(K) M, C and k D(K) ≧ D(M) & -- 15 75 45 D(K) ≧ D(C) Y, M, C and K D(M) > D(C) & 0 45 15 75 D(M) > D(K) Y, M, C and k D(C) ≧ D(M) & 0 15 45 75 D(C) > D(K) Y, M, C and k D(K) ≧ D(M) & 0 15 75 45 D(K) ≧ D(C) ______________________________________ where D(Y), D(M), D(C), and D(K) denote dot percentages of yellow, magenta, cyan, and black, respectively, "N/A" means that there are no conditions for the relations among the dot percentages D(Y), D(M), D(C), and D(K), and "15/75" means arbitrary one of 15° and 75°.

Claim 11

An apparatus for generating a dot signal for a plurality of color separations to record a halftone image of each color separation, comprising: area dividing means for dividing a whole image area into a plurality of image areas; screen angle assigning means for assigning a set of screen angles for said plurality of color separations with respect to each of said plurality of image areas; a first memory for storing a plurality of color-separated image signals for said plurality of color separations, said plurality of color-separated image signals representing a color image in said whole image area; a second memory for storing a plurality of screen pattern data for said plurality of color separations; selection means for selecting one of said plurality of screen pattern data for each color separation in each of said plurality of image areas according to said assigned set of screen angles assigned to each of said plurality of image areas; and a dot signal generator for comparing the selected screen pattern data with the color-separated image data for each separation, to thereby generate a dot signal for recording a halftone image of each color separation, wherein said plurality of color separations include four color separations for yellow, magenta, cyan and black inks and said apparatus, further comprising: a third memory for storing mode data assigned to each of the plurality of image areas, the mode data representing a first mode where screen angles of the four color separations are set at predetermined standard values, and a second mode when the screen angles of the four color separations are adjusted from the predetermined standard values; and screen angle data generating means for producing the screen angle data representing screen angles 0(Y), 0(M), 0(C), and 0(K) for yellow, magenta, cyan and black, respectively, according to the following Table B with respect to pixels to which the mode data indicating the second mode is assigned: TABLE B ______________________________________ COLOR RELATIONS SEPARATION OF DOT % SCREEN ANGLES NEITHER D(Y), D(M), θ θ θ θ 100%/0% D(C), D(K) (Y) (M) (C) (K) ______________________________________ Y N/A 45 -- -- -- M N/A -- 45 -- -- C N/A -- -- 45 -- K N/A -- -- -- 45 Y and M N/A 0 45 -- -- Y and C N/A 0 -- 45 -- Y and K N/A 0 -- -- 45 M and C D(M) > D(C) -- 45 15 -- M and C D(M) ≦ D(C) -- 15 45 -- M and K D(M) > D(K) -- 45 -- 75 M and K D(M) ≦ D(K) -- 15 -- 45 C and K D(C) > D(K) -- -- 45 75 C and K D(C) ≦ D(K) -- -- 15 45 Y, M and C D(M) > D(C) 15/75 45 0 -- Y, M and C D(M) ≦ D(C) 15/75 0 45 -- Y, M and K D(M) > D(K) 15/75 45 -- 0 Y, M and K D(M) ≦ D(K) 15/75 0 -- 45 Y, C and K D(C) > D(K) 15/75 -- 45 0 Y, C and K D(C) ≦ D(K) 15/75 -- 0 45 M, C and K D(M) > D(C) & -- 45 15 75 D(M) > D(K) M, C and k D(C) ≧ D(M) & -- 15 45 75 D(C) > D(K) M, C and k D(K) ≧ D(M) & -- 15 75 45 D(K) ≧ D(C) Y, M, C and K D(M) > D(C) & 0 45 15 75 D(M) > D(K) Y, M, C and k D(C) ≧ D(M) & 0 15 45 75 D(C) > D(K) Y, M, C and k D(K) ≧ D(M) & 0 15 75 45 D(K) ≧ D(C) ______________________________________ where D(Y), D(M), D(C), and D(K) denote dot percentages of yellow, magenta, cyan, and black, respectively, "N/A" means that there are no conditions for the relations among the dot percentages D(Y), D(M), D(C), and D(K), and "15/75" means arbitrary one of 15° and 75°.

Claim 12

A method for generating a dot signal for a plurality of color separations to record a halftone image of each color separation, comprising the steps of: dividing a whole image area into a plurality of image areas; assigning a set of screen angles for said plurality of color separations with respect to each of said plurality of image areas; storing a plurality of color-separated image signals for said plurality of color separations, said plurality of color-separated image signals representing a color image in said whole image area; storing a plurality of screen pattern data for said plurality of color separations; selecting one of said plurality of screen pattern data for each color separation in each of said plurality of image areas according to said assigned set of screen angles assigned to each of said plurality of image areas; and comparing the selected screen pattern data with the color-separated image data for each separation, to thereby generate a dot signal for recording a halftone image of each color separation, wherein said plurality of color separations include four separations for yellow, magenta, cyan and black inks, and said method further comprises the steps of: specifying mode data for each of the plurality of image areas, the mode data representing a first mode where screen angles of the four color separations are set at predetermined standard values, and a second mode where the screen angles of the four color separations are adjusted from the predetermined standard values, and producing the screen angle data representing screen angles θ(Y), θ(M), θ(C), and θ(K) for yellow, magenta, cyan, and black, respectively, according to the following Table B with respect to pixels to which the mode data indicating the second mode is assigned: TABLE B ______________________________________ COLOR RELATIONS SEPARATION OF DOT % SCREEN ANGLES NEITHER D(Y), D(M), θ θ θ θ 100%/0% D(C), D(K) (Y) (M) (C) (K) ______________________________________ Y N/A 45 -- -- -- M N/A -- 45 -- -- C N/A -- -- 45 -- K N/A -- -- -- 45 Y and M N/A 0 45 -- -- Y and C N/A 0 -- 45 -- Y and K N/A 0 -- -- 45 M and C D(M) > D(C) -- 45 15 -- M and C D(M) ≦ D(C) -- 15 45 -- M and K D(M) > D(K) -- 45 -- 75 M and K D(M) ≦ D(K) -- 15 -- 45 C and K D(C) > D(K) -- -- 45 75 C and K D(C) ≦ D(K) -- -- 15 45 Y, M and C D(M) > D(C) 15/75 45 0 -- Y, M and C D(M) ≦ D(C) 15/75 0 45 -- Y, M and K D(M) > D(K) 15/75 45 -- 0 Y, M and K D(M) ≦ D(K) 15/75 0 -- 45 Y, C and K D(C) > D(K) 15/75 -- 45 0 Y, C and K D(C) ≦ D(K) 15/75 -- 0 45 M, C and K D(M) > D(C) & -- 45 15 75 D(M) > D(K) M, C and k D(C) ≧ D(M) & -- 15 45 75 D(C) > D(K) M, C and k D(K) ≧ D(M) & -- 15 75 45 D(K) ≧ D(C) Y, M, C and K D(M) > D(C) & 0 45 15 75 D(M) > D(K) Y, M, C and k D(C) ≧ D(M) & 0 15 45 75 D(C) > D(K) Y, M, C and k D(K) ≧ D(M) & 0 15 75 45 D(K) ≧ D(C) ______________________________________ where D(Y), D(M), D(C), and D(K) denote dot percentages of yellow, magenta, cyan, and black, respectively, "N/A" means that there are no conditions for the relations among the dot percentages D(Y), D(M), D(C), and D(K), and "15/75" means arbitrary one of 15° and 75°.

Claim 13

A method for generating a dot signal for a plurality of color separations to record a halftone image of each color separation, comprising the steps of: dividing a whole image area into a plurality of image areas; assigning a set of screen angles for said plurality of color separations with respect to each of said plurality of image areas; storing a plurality of color-separated image signals for said plurality of color separations, said plurality of color-separated image signals representing a color image in said whole image area; storing a plurality of screen pattern data for said plurality of color separations; selecting one of said plurality of screen pattern data for each color separation in each of said plurality of image areas according to said assigned set of screen angles assigned to each of said plurality of image areas; and comparing the selected screen pattern data with the color-separated image data for each separation, to thereby generate a dot signal for recording a halftone image of each color separation, wherein said plurality of color separations include four separations for yellow, magenta, cyan and black inks, and said method further comprises the steps of: specifying mode data for each of the plurality of image areas, the mode data representing a first mode where screen angles of the four color separations are set at predetermined standard values, and a second mode where the screen angles of the four color separations are adjusted from the predetermined standard values, and producing the screen angle data representing screen angles θ(Y), θ(M), θ(C), and θ(K) for yellow, magenta, cyan, and black, respectively, according to the following Table B with respect to pixels to which the mode data indicating the second mode is assigned: TABLE B ______________________________________ COLOR RELATIONS SEPARATION OF DOT % SCREEN ANGLES NEITHER D(Y), D(M), θ θ θ θ 100%/0% D(C), D(K) (Y) (M) (C) (K) ______________________________________ Y N/A 45 -- -- -- M N/A -- 45 -- -- C N/A -- -- 45 -- K N/A -- -- -- 45 Y and M N/A 0 45 -- -- Y and C N/A 0 -- 45 -- Y and K N/A 0 -- -- 45 M and C D(M) > D(C) -- 45 15 -- M and C D(M) ≦ D(C) -- 15 45 -- M and K D(M) > D(K) -- 45 -- 75 M and K D(M) ≦ D(K) -- 15 -- 45 C and K D(C) > D(K) -- -- 45 75 C and K D(C) ≦ D(K) -- -- 15 45 Y, M and C D(M) > D(C) 15/75 45 0 -- Y, M and C D(M) ≦ D(C) 15/75 0 45 -- Y, M and K D(M) > D(K) 15/75 45 -- 0 Y, M and K D(M) ≦ D(K) 15/75 0 -- 45 Y, C and K D(C) > D(K) 15/75 -- 45 0 Y, C and K D(C) ≦ D(K) 15/75 -- 0 45 M, C and K D(M) > D(C) & -- 45 15 75 D(M) > D(K) M, C and k D(C) ≧ D(M) & -- 15 45 75 D(C) > D(K) M, C and k D(K) ≧ D(M) & -- 15 75 45 D(K) ≧ D(C) Y, M, C and K D(M) > D(C) & 0 45 15 75 D(M) > D(K) Y, M, C and k D(C) ≧ D(M) & 0 15 45 75 D(C) > D(K) Y, M, C and k D(K) ≧ D(M) & 0 15 75 45 D(K) ≧ D(C) ______________________________________ where D(Y), D(M), D(C), and D(K) denote dot percentages of yellow, magenta, cyan, and black, respectively, "N/A" means that there are no conditions for the relations among the dot percentages D(Y), D(M), D(C), and D(K), and "15/75" means arbitrary one of 15° and 75°.

Claim 14

A method for generating a dot signal for a plurality of color separations to record a halftone image of each color separation, comprising the steps of: dividing a whole image area into a plurality of image areas; assigning a set of screen angles for said plurality of color separations with respect to each of said plurality of image areas; storing a plurality of color-separated image signals for said plurality of color separations, said plurality of color-separate image signals representing a color image in said whole image area; storing a plurality of screen pattern data for said plurality of color separations; selecting one of said plurality of screen pattern data for each color separation in each of said plurality of image areas according to said assigned set of screen angles assigned to each of said plurality of image areas; and comparing the selected screen pattern data with the color-separated image data for each separation, to thereby generate a dot signal for recording a halftone image of each color separation, wherein said plurality of color separations include four separations for yellow, magenta, cyan and black inks, and said method further comprises the step of: specifying reference data for an overlapping area, the overlapping area being formed between first and second image areas so that a density of each of four color separations of said overlapping area is equal to one of the first and second image areas, said reference data indicating, with respect to each of the magenta and cyan separations, which one of two screen angles for the first and second image areas is used as a screen angle of the overlapping area.

Claim 15

A method for generating a dot signal for a plurality of color separations to record a halftone image of each color separation, comprising the steps of: dividing a whole image area into a plurality of image areas; assigning a set of screen angles for said plurality of color separations with respect to each of said plurality of image areas; storing a plurality of color-separated image signals for said plurality of color separations, said plurality of color-separate image signals representing a color image in said whole image area; storing a plurality of screen pattern data for said plurality of color separations; selecting one of said plurality of screen pattern data for each color separation in each of said plurality of image areas according to said assigned set of screen angles assigned to each of said plurality of image areas; and comparing the selected screen pattern data with the color-separated image data for each separation, to thereby generate a dot signal for recording a halftone image of each color separation, wherein said plurality of color separations include four separations for yellow, magenta, cyan and black inks, and said method further comprises the step of: specifying reference data for an overlapping area, the overlapping area being formed between first and second image areas so that a density of each of four color separations of said overlapping area is equal to one of the first and second image areas, said reference data indicating, with respect to each of the magenta and cyan separations, which one of two screen angles for the first and second image areas is used as a screen angle of the overlapping area.

Claim 16

A method for generating a dot signal for a plurality of color separations to record a halftone image of each color separation, comprising the steps of: dividing a whole image area into a plurality of image areas; assigning a set of screen angles for said plurality of color separations with respect to each of said plurality of image areas; storing a plurality of color-separated image signals for said plurality of color separations, said plurality of color-separated image signals representing a color image in said whole image area; storing a plurality of screen pattern data for said plurality of color separations; selecting one of said plurality of screen pattern data for each color separation in each of said plurality of image areas according to said assigned set of screen angles assigned to each of said plurality of image areas; and comparing the selected screen pattern data with the color-separated image data for each separation, to thereby generate a dot signal for recording a halftone image of each color separation, wherein said plurality of color separations include four separations for yellow, magenta, cyan and black inks, and said method further comprises the steps of: specifying mode data for each of the plurality of image areas, the mode data representing a first mode where screen angles of the magenta and cyan separations are set at predetermined standard values, and a second mode where the screen angles of the magenta and cyan separations are exchanged each other from the predetermined standard values; and producing the screen angle data of the magenta and cyan separations according to the mode data.

Claim 17

A method for generating a dot signal for a plurality of color separations to record a halftone image of each color separation, comprising the steps of: dividing a whole image area into a plurality of image areas; assigning a set of screen angles for said plurality of color separations with respect to each of said plurality of image areas; storing a plurality of color-separated image signals for said plurality of color separations, said plurality of color-separated image signals representing a color image in said whole image area; storing a plurality of screen pattern data for said plurality of color separations; selecting one of said plurality of screen pattern data for each color separation in each of said plurality of image areas according to said assigned set of screen angles assigned to each of said plurality of image areas; and comparing the selected screen pattern data with the color-separated image data for each separation, to thereby generate a dot signal for recording a halftone image of each color separation, wherein said plurality of color separations include four separations for yellow, magenta, cyan and black inks, and said method further comprises the steps of: specifying mode data for each of the plurality of image areas, the mode data representing a first mode where screen angles of the magenta and cyan separations are set at predetermined standard values, and a second mode where the screen angles of the magenta and cyan separations are exchanged each other from the predetermined standard values; and producing the screen angle data of the magenta and cyan separations according to the mode data.

Claim 21

A method for generating a dot signal for a plurality of color separations to record a halftone image of each color separation, comprising the steps of: dividing a whole image area into a plurality of image areas; assigning a set of screen angles for said plurality of color separations with respect to each of said plurality of image areas; storing a plurality of color-separated image signals for said plurality of color separations, said plurality of color-separated image signals representing a color image in said whole image area; storing a plurality of screen pattern data for said plurality of color separations; selecting one of said plurality of screen pattern data for each color separation in each of said plurality of image areas according to said assigned set of screen angles assigned to each of said plurality of image areas; and comparing the selected screen pattern data with the color-separated image data for each separation, to thereby generate a dot signal for recording a halftone image of each color separation, wherein said plurality of color separations include four separations for yellow, magenta, cyan and black inks, and said method further comprises the steps of: specifying mode data for each of the plurality of image areas, the mode data representing a first mode where screen angles of the four color separations are set at predetermined standard values, and a second mode where the screen angles of the four color separations are adjusted from the predetermined standard values; and producing the screen angle data representing screen angles θ(Y), θ(M), θ(C), and θ(K) for yellow, magenta, cyan and black, respectively, according to the following Table A with respect to pixels to which the mode data indicating the second mode is assigned: TABLE A ______________________________________ COLOR RELATIONS SEPARATION OF DOT % SCREEN ANGLES NEITHER D(Y), D(M), θ θ θ θ 100%/0% D(C), D(K) (Y) (M) (C) (K) ______________________________________ Y N/A 45 -- -- -- M N/A -- 45 -- -- C N/A -- -- 45 -- K N/A -- -- -- 45 Y and M N/A 0 45 -- -- Y and C N/A 0 -- 45 -- Y and K N/A 0 -- -- 45 M and C D(M) > D(C) -- 45 0 -- M and C D(M) ≦ D(C) -- 0 45 -- M and K D(M) > D(K) -- 45 -- 0 M and K D(M) ≦ D(K) -- 0 -- 45 C and K D(C) > D(K) -- -- 45 0 C and K D(C) ≦ D(K) -- -- 0 45 Y, M and C D(M) > D(C) 75 45 15 -- Y, M and C D(M) ≦ D(C) 75 15 45 -- Y, M and K D(M) > D(K) 75 45 -- 15 Y, M and K D(M) ≦ D(K) 75 15 -- 45 Y, C and K D(C) > D(K) 75 -- 45 15 Y, C and K D(C) ≦ D(K) 75 -- 15 45 M, C and K D(M) > D(C) & -- 45 15 75 D(M) > D(K) M, C and k D(C) ≧ D(M) & -- 15 45 75 D(C) > D(K) M, C and k D(K) ≧ D(M) & -- 15 75 45 D(K) ≧ D(C) Y, M, C and K D(M) > D(C) & 0 45 15 75 D(M) > D(K) Y, M, C and k D(C) ≧ D(M) & 0 15 45 75 D(C) > D(K) Y, M, C and k D(K) ≧ D(M) & 0 15 75 45 D(K) ≧ D(C) ______________________________________ where D(Y), D(M), D(C), and D(K) denote dot percentages of yellow, magenta, cyan and black, respectively, "N/A" means that there are no conditions for the relations among the dot percentages D(Y), D(M), D(C), and D(K).

Claim 22

A method for generating a dot signal for a plurality of color separations to record a halftone image of each color separation, comprising the steps of: dividing a whole image area into a plurality of image areas; assigning a set of screen angles for said plurality of color separations with respect to each of said plurality of image areas; storing a plurality of color-separated image signals for said plurality of color separations, said plurality of color-separated image signals representing a color image in said whole image area; storing a plurality of screen pattern data for said plurality of color separations; selecting one of said plurality of screen pattern data for each color separation in each of said plurality of image areas according to said assigned set of screen angles assigned to each of said plurality of image areas; and comparing the selected screen pattern data with the color-separated image data for each separation, to thereby generate a dot signal for recording a halftone image of each color separation, wherein said plurality of color separations include four separations for yellow, magenta, cyan and black inks, and said method further comprises the steps of: specifying mode data for each of the plurality of image areas, the mode data representing a first mode where screen angles of the four color separations are set at predetermined standard values, and a second mode where the screen angles of the four color separations are adjusted from the predetermined standard values; and producing the screen angle data representing screen angles θ(Y), θ(M), θ(C), and θ(K) for yellow, magenta, cyan and black, respectively, according to the following Table A with respect to pixels to which the mode data indicating the second mode is assigned: TABLE A ______________________________________ COLOR RELATIONS SEPARATION OF DOT % SCREEN ANGLES NEITHER D(Y), D(M), θ θ θ θ 100%/0% D(C), D(K) (Y) (M) (C) (K) ______________________________________ Y N/A 45 -- -- -- M N/A -- 45 -- -- C N/A -- -- 45 -- K N/A -- -- -- 45 Y and M N/A 0 45 -- -- Y and C N/A 0 -- 45 -- Y and K N/A 0 -- -- 45 M and C D(M) > D(C) -- 45 0 -- M and C D(M) ≦ D(C) -- 0 45 -- M and K D(M) > D(K) -- 45 -- 0 M and K D(M) ≦ D(K) -- 0 -- 45 C and K D(C) > D(K) -- -- 45 0 C and K D(C) ≦ D(K) -- -- 0 45 Y, M and C D(M) > D(C) 75 45 15 -- Y, M and C D(M) ≦ D(C) 75 15 45 -- Y, M and K D(M) > D(K) 75 45 -- 15 Y, M and K D(M) ≦ D(K) 75 15 -- 45 Y, C and K D(C) > D(K) 75 -- 45 15 Y, C and K D(C) ≦ D(K) 75 -- 15 45 M, C and K D(M) > D(C) & -- 45 15 75 D(M) > D(K) M, C and k D(C) ≧ D(M) & -- 15 45 75 D(C) > D(K) M, C and k D(K) ≧ D(M) & -- 15 75 45 D(K) ≧ D(C) Y, M, C and K D(M) > D(C) & 0 45 15 75 D(M) > D(K) Y, M, C and k D(C) ≧ D(M) & 0 15 45 75 D(C) > D(K) Y, M, C and k D(K) ≧ D(M) & 0 15 75 45 D(K) ≧ D(C) ______________________________________ where D(Y), D(M), D(C), and D(K) denote dot percentages of yellow, magenta, cyan and black, respectively, "N/A" means that there are no conditions for the relations among the dot percentages D(Y), D(M), D(C), and D(K).