Image forming apparatus and method thereof
First Claim
1. An image forming apparatus for digitally reproducing a color image using a screen set consisting of a halftone screen for each color, the screen set comprising:
- a first-color halftone screen having an associated first halftone pitch;
a second-color halftone screen having an associated second halftone pitch measured in a corresponding direction to the first halftone pitch,a third-color halftone screen; and
a fourth-color halftone screen, whereintwo first screen vectors, one in each of the first and second-color halftone screens, each first screen vector being in a spatial frequency domain defined by a basis vector of a halftone dot pattern of the respective halftone screen, are parallel to each other,two second screen vectors, one in each of the first and second-color halftone screens, each second screen vector being in a spatial frequency domain defined by a basis vector of a halftone dot pattern of the respective halftone screen, are not parallel to each other,two second screen vectors, one in each of the third and fourth-color halftone screens, each second screen vector being in a spatial frequency domain defined by a basis vector of a halftone dot pattern of the respective halftone screen, are parallel to each other, andtwo first screen vectors, one in each of the third and fourth-color halftone screens, each first screen vector being in a spatial frequency domain defined by a basis vector of a halftone dot pattern of the respective halftone screen, are not parallel to each other.
1 Assignment
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Accused Products
Abstract
To reduce low-frequency moiré in secondary colors and tertiary colors in four color screens, between at least two halftone screens, screen vectors wa2, wb2 are arranged to match each other, while other screen vectors are arranged not to match each other. A halftone screen is an orthogonal screen in which screen vector wa2 is perpendicular to basis vector ra1. A halftone screen is a non-orthogonal screen in which screen vector wb2 is perpendicular to basis vector rb1. When screen vector wa2 matches screen vector wb2, spatial frequency spectra corresponding to screen vectors wa2 and wab2, match each other. With such a relationship, because a pair of spatial frequency spectra can match each other between two colors, wider intervals can be provided for the spatial frequency spectra of the remaining colors of four colors, which would suppress low-frequency moiré.
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Citations
15 Claims
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1. An image forming apparatus for digitally reproducing a color image using a screen set consisting of a halftone screen for each color, the screen set comprising:
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a first-color halftone screen having an associated first halftone pitch; a second-color halftone screen having an associated second halftone pitch measured in a corresponding direction to the first halftone pitch, a third-color halftone screen; and a fourth-color halftone screen, wherein two first screen vectors, one in each of the first and second-color halftone screens, each first screen vector being in a spatial frequency domain defined by a basis vector of a halftone dot pattern of the respective halftone screen, are parallel to each other, two second screen vectors, one in each of the first and second-color halftone screens, each second screen vector being in a spatial frequency domain defined by a basis vector of a halftone dot pattern of the respective halftone screen, are not parallel to each other, two second screen vectors, one in each of the third and fourth-color halftone screens, each second screen vector being in a spatial frequency domain defined by a basis vector of a halftone dot pattern of the respective halftone screen, are parallel to each other, and two first screen vectors, one in each of the third and fourth-color halftone screens, each first screen vector being in a spatial frequency domain defined by a basis vector of a halftone dot pattern of the respective halftone screen, are not parallel to each other. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 15)
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12. An image forming method for digitally reproducing a color image, comprising:
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generating halftone images from input color images using a screen set consisting of multiple color halftone screens, the screen set comprises a first-color halftone screen having an associated first halftone pitch, a second-color halftone screen having an associated second halftone pitch measured in a corresponding direction to the first halftone pitch, a third-color halftone screen; and
a fourth-color halftone screen, whereintwo first screen vectors, one in each halftone screen, each first screen vector being in a spatial frequency domain defined by a basis vector of a halftone dot pattern of the respective halftone screen, are parallel to each other, two second screen vectors, one in each halftone screen, each second screen vector being in a spatial frequency domain defined by a basis vector of a halftone dot pattern of the respective halftone screen, are not parallel to each other, two second screen vectors, one in each of the third and fourth-color halftone screens, each second screen vector being in a spatial frequency domain defined by a basis vector of a halftone dot pattern of the respective halftone screen, are parallel to each other, and two first screen vectors, one in each of the third and fourth-color halftone screens, each first screen vector being in a spatial frequency domain defined by a basis vector of a halftone dot pattern of the respective halftone screen, are not parallel to each other, reproducing said input color images by combining said halftone images. - View Dependent Claims (13, 14)
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Specification