To reduce low-frequency moire 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 moire.