Multilevel screening for color laser printer

An apparatus for accurate reduced-resolution tone reproduction of a printed image based on an image of image values, said printed image being generated by a printer engine with a printer resolution which deposits a marking medium at pixels on a printing surface, an amount of said marking medium deposited at said pixels being a function of printer values for said pixels, comprising:

• cell definition unit for defining dimensions of a multi-pixel cell of said pixels;
• font cell generator for defining a set of font cells, each of said font cells having an arrangement of font pixel values for said pixels in said multi-pixel cell and a corresponding font index value;
• and
• halftone font indexer for mapping said image values for said pixels in said multi-pixel cell to a corresponding one of said font cells, said printer engine printing said font pixel values for said corresponding one of said font cells in said multi-pixel cell on said printing surface.

An apparatus for accurate reduced-resolution tone reproduction of a printed image based on an image of image values, said printed image being generated by a printer engine with a printer resolution which deposits a marking medium at pixels on a printing surface, an amount of said marking medium deposited at said pixels being a function of printer values for said pixels, comprising:

• means for defining dimensions of a multi-pixel cell of said pixels;
• means for defining a set of font cells, each of said font cells having an arrangement of font pixel values for said pixels in said multi-pixel cell and a corresponding font index value;
• and
• means for mapping said image values for said pixels in said multi-pixel cell to a corresponding one of said font cells, said printer engine printing said font pixel values for said corresponding one of said font cells in said multi-pixel cell on said printing surface.

A system for printing a reduced-resolution image of image values on a printing surface with accurate tone reproduction, comprising:

• a printer engine with a printer resolution which deposits a marking medium at pixels on said printing surface, an amount of said marking medium deposited at said pixels being a function of printer values for said pixels;
• a printer engine for depositing marking medium on said printing surface;
• cell dimensions definition unit for defining dimensions of a multi-pixel cell of said pixels;
• font cell generator for providing a set of font cells, each of said font cells having an arrangement of font pixel values for said pixels in said multi-pixel cell and a corresponding font index value;
• and
• halftone font indexer for mapping said image values for said pixels in said multi-pixel cell to a corresponding one of said font cells, said printer engine printing said font pixel values for said corresponding one of said font cells in said multi-pixel cell on said printing surface.

A method for accurate reduced-resolution tone reproduction of a printed image based on an image of image values obtained via a scanner, said printed image being generated by a printer engine with a printer resolution which deposits a marking medium at pixels on a printing surface, an amount of said marking medium deposited at said pixels being a function of printer values for said pixels, comprising the steps of:

• calibrating printer colors generated by said printer engine with said image values obtained from said scanner to produce calibrated image values;
• filtering said calibrated image values to provide filtered values lighter than said calibrated image values in highlight and upper midtone regions and darker than said calibrated image values in shadow and lower midtone regions, said filtered values being quantized on a filtered values scale having a maximum filtered value and more than two filtered scale levels;
• mapping said filtered values for said pixels to printer values, said printer values being quantized on a printer values scale having more than two printer scale levels and a maximum printer value which differs from said maximum filtered value, differences between said filtered values and said printer values, as measured on said filtered values scale, being corrected such that a first spatial average over a region of said filtered values approximates a second spatial average over said region of said printer values, as measured on said filtered values scale;
• defining dimensions of a multi-pixel cell of said pixels;
• defining a set of font cells, each of said font cells having an arrangement of font pixel values for said pixels in said multi-pixel cell and a corresponding font index value;
• mapping said printer values for said pixels in said multi-pixel cell to a corresponding one of said font cells, said printer engine printing said font pixel values for said corresponding one of said font cells in said multi-pixel cell on said printing surface;
• and
• adjusting a dynamic range of said font cells as printed by said printer engine to provide an extended dynamic range.

An apparatus for accurate reduced-resolution tone reproduction of a printed image based on an image of image values obtained via a scanner, said printed image being generated by a printer engine with a printer resolution which deposits a marking medium at pixels on a printing surface, an amount of said marking medium deposited at said pixels being a function of printer values for said pixels, comprising:

• means for calibrating printer colors generated by said printer engine with said image values obtained from said scanner to produce calibrated image values;
• means for filtering said calibrated image values to provide filtered values lighter than said calibrated image values in highlight and upper midtone regions and darker than said calibrated image values in shadow and lower midtone regions, said filtered values being quantized on a filtered values scale having a maximum filtered value and more than two filtered scale levels;
• means for mapping said filtered values for said pixels to printer values, said printer values being quantized on a printer values scale having more than two printer scale levels and a maximum printer value which differs from said maximum filtered value, differences between said filtered values and said printer values, as measured on said filtered values scale, being corrected such that a first spatial average over a region of said filtered values approximates a second spatial average over said region of said printer values, as measured on said filtered values scale;
• means for defining dimensions of a multi-pixel cell of said pixels;
• means for defining a set of font cells, each of said font cells having an arrangement of font pixel values for said pixels in said multi-pixel cell and a corresponding font index value;
• means for mapping said printer values for said pixels in said multi-pixel cell to a corresponding one of said font cells, said printer engine printing said font pixel values for said corresponding one of said font cells in said multi-pixel cell on said printing surface;
• and
• means for dynamic range adjustment of a dynamic range of said font cells as printed by said printer engine to provide an extended dynamic range.

An apparatus for accurate reduced-resolution tone reproduction of a printed image based on an image of image values obtained via a scanner, said printed image being generated by a printer engine with a printer resolution which deposits a marking medium at pixels on a printing surface, an amount of said marking medium deposited at said pixels being a function of printer values for said pixels, comprising:

• color matcher for calibrating printer colors generated by said printer engine with said image values obtained from said scanner to produce calibrated image values;
• dot gain compensator for filtering said calibrated image values to provide filtered values lighter than said calibrated image values in highlight and upper midtone regions and darker than said calibrated image values in shadow and lower midtone regions, said filtered values being quantized on a filtered values scale having a maximum filtered value and more than two filtered scale levels;
• halftoning unit for mapping said filtered values for said pixels to printer values, said printer values being quantized on a printer values scale having more than two printer scale levels and a maximum printer value which differs from said maximum filtered value, differences between said filtered values and said printer values, as measured on said filtered values scale, being corrected such that a first spatial average over a region of said filtered values approximates a second spatial average over said region of said printer values, as measured on said filtered values scale;
• cell dimensions definition unit for defining dimensions of a multi-pixel cell of said pixels;
• font cell generator for generating a set of font cells, each of said font cells having an arrangement of font pixel values for said pixels in said multi-pixel cell and a corresponding font index value;
• halftone font indexer for mapping said printer values for said pixels in said multi-pixel cell to a corresponding one of said font cells, said printer engine printing said font pixel values for said corresponding one of said font cells in said multi-pixel cell on said printing surface;
• and
• dynamic range adjuster for dynamic range adjustment of a dynamic range of said font cells as printed by said printer engine to provide an extended dynamic range.