Electrophotographic image forming apparatus and image forming program product therefor

An electrophotographic image forming apparatus, using a halftone spot consisting of multiple dot images formed in pixel areas so as to represent a gray scale and to reproduce an image, comprising:

• a halftone processor for generating image reproduction data for each pixel by referring to a transformation table wherein gray level data for said image and correlated image reproduction data are stored;
• wherein said transformation table includes:
• first look-up tables that each store gray level data and correlated first image reproduction data, including size data for virtual dots, each of which corresponds to one of said dot images;
• second look-up tables that each store gray level data and correlated second image reproduction data, including size data for virtual dots, each of which corresponds to one of said dot images;
• and a pattern matrix, elements of which are correlated with multiple pixels in a predetermined area of an image and each indicate one of said first look-up tables and one of said second look-up tables that are to be referred to;
• and
• wherein number of said first look-up tables and number of said second look-up tables is smaller than number of elements of said pattern matrix.

An electrophotographic image forming program product, using a halftone spot consisting of multiple dot images formed in pixel areas so as to represent a gray scale and to reproduce an image, permitting a computer to perform:

• a halftone process for generating image reproduction data for each pixel by referring to a transformation table wherein gray level data for said image and correlated image reproduction data are stored, wherein said transformation table includes:
• look-up tables, in each of which gray level data and correlated image reproduction data are stored;
• and
• a pattern matrix, elements of which are so correlated with multiple pixels in a predetermined area of an image that each indicates a look-up table to be referred to;
• and wherein said image reproduction data stored by each of said look-up tables includes size data and position data for virtual dots, each of which corresponds to one of said multiple dot images.

An electrophotographic image forming program product, using a halftone spot consisting of multiple dot images formed in pixel areas so as to represent a gray scale and to reproduce an image, permitting a computer to perform:

• a halftone process for generating image reproduction data for each pixel by referring to a transformation table wherein gray level data for said image and correlated image reproduction data are stored;
• wherein said transformation table includes:
• first look-up tables that each store gray level data and correlated first image reproduction data, including size data for virtual dots, each of which corresponds to one of said dot images;
• second look-up tables that each store gray level data and correlated second image reproduction data, including size data for virtual dots, each of which corresponds to one of said dot images;
• and a pattern matrix, elements of which are correlated with multiple pixels in a predetermined area of an image and each indicate one of said first look-up tables and one of said second look-up tables that are to be referred to;
• and
• wherein number of said first look-up tables and number of said second look-up tables is smaller than number of pixels in said pattern matrix.

An electrophotographic image forming apparatus, using a halftone spot consisting of multiple dot images formed in pixel areas so as to represent a gray scale and to reproduce an image, comprising:

• a halftone processor in the electrophotographic image forming apparatus for generating image reproduction data for each pixel by referring to a transformation table wherein gray level data for said image and correlated image reproduction data are stored,
• wherein said transformation table includes:
• look-up tables in which gray level data are stored along with correlated image reproduction data, and
• a pattern matrix, elements of which are correlated with multiple pixels in a predetermined area of the image and each indicate one of said look-up tables to be referred to, and
• wherein, in addition to said look-up tables to be referred to, said pattern matrix includes position data for virtual dots, which each correspond to one of said dotted images.