Process for specifying mean-preserving mutli-level halftone matrices with varying amounts of modulation
First Claim
1. In a multi-level halftoning system, apparatus for generating a multi-level pixel value for a halftone cell from a magnitude of an intensity value, said apparatus comprising:
- means, responsive to the magnitude of said intensity value, for producing a modulation level as said multi-level pixel value, wherein said producing means comprises a plurality of look-up tables each having values representing a pre-defined transfer function, wherein said pre-defined transfer functions are generated by apparatus comprising;
means for automatically producing said transfer functions using a mean-preserving process such that a sum of the derivative of said transfer functions equals the number of pixel values in said halftone cell;
preference matrix means connected to said producing means, for selecting one of said plurality of look-up tables; and
means, connected to said selecting means, for controlling said selection such that one look-up table is selected in a pre-defined manner to produce a modulation level as said multi-level pixel value.
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Abstract
Apparatus and a method for generating a multi-level halftone image (104) from a digitally sampled continuous tone (contone) image (101). The apparatus includes a control circuit (140), a preference matrix (150) having as its matrix elements addresses of a plurality of look-up tables (160) and a plurality of look-up tables (160) in the form of a look-up table stack (155). The control circuit instructs the preference matrix to select a specific look-up table from the look-up table stack in a pre-defined manner. The selected table is used to convert an intensity value (102) into each multi-level pixel value (106) in the halftone image. To accomplish the conversion, each look-up table contains a quantized one-dimensional transfer function (165'"'"') having as an input the magnitude of the intensity value. The transfer functions are automatically generated such that the sum of the derivatives of the transfer functions equals the number of pixel values in a halftone cell. The magnitude of each intensity value is mapped into an output level by the quantized transfer function as one of a plurality of available levels. The resulting output level is assigned a pixel location in a halftone cell (103). The look-up table selection is repeated for each element of the preference matrix such that the magnitude of each different intensity value in the contone image is mapped into a corresponding halftone cell to generate a complete multi-level halftone image.
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Citations
22 Claims
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1. In a multi-level halftoning system, apparatus for generating a multi-level pixel value for a halftone cell from a magnitude of an intensity value, said apparatus comprising:
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means, responsive to the magnitude of said intensity value, for producing a modulation level as said multi-level pixel value, wherein said producing means comprises a plurality of look-up tables each having values representing a pre-defined transfer function, wherein said pre-defined transfer functions are generated by apparatus comprising; means for automatically producing said transfer functions using a mean-preserving process such that a sum of the derivative of said transfer functions equals the number of pixel values in said halftone cell; preference matrix means connected to said producing means, for selecting one of said plurality of look-up tables; and means, connected to said selecting means, for controlling said selection such that one look-up table is selected in a pre-defined manner to produce a modulation level as said multi-level pixel value. - View Dependent Claims (2, 3, 4, 5, 6)
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7. In a multi-level halftoning system, a method for generating a multi-level pixel value for a halftone cell from an intensity value having a magnitude, said method comprising the steps of:
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generating a plurality of pre-defined transfer functions wherein a sum of the derivative of said transfer functions equals a number of pixel values in said halftone cell; selecting one of a plurality of look-up tables, wherein each said look-up table contains values representing one of said pre-defined transfer functions; controlling said selection such that one look-up table is selected in a pre-defined manner; and producing, in response to the magnitude of said intensity value, a modulation level as said multi-level pixel value. - View Dependent Claims (8, 9, 10, 11)
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12. In a multi-level halftoning system for converting an input intensity value into a multi-level pixel value for a halftone cell, apparatus for specifying matrix values used as modulation levels for converting said intensity value comprising:
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means for generating a plurality of transfer functions being mean preserving such that a sum of the derivatives of said transfer functions equals a number of pixel values in said halftone cell; and means for specifying modulation levels from said mean preserving transfer functions. - View Dependent Claims (13, 14, 15)
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16. In a multi-level halftoning system having a predetermined number of micro-output levels available in the system, a method for generating a multi-level pixel value for a halftone cell, wherein said halftone cell has a predetermined cell size, from an intensity value having a given magnitude, comprising the steps of:
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a. generating a plurality of pre-defined transfer functions wherein the sum of the derivative of said transfer function equals a number of pixel values in said halftone cell and further wherein each transfer function is quantized into a plurality of modulation levels determined as a function of the size of the halftone cell and the number of micro-output levels available in the system; and b. assigning said modulation levels as threshold matrix entries in a set of modulation level matrices. - View Dependent Claims (17)
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18. In a multi-level halftoning system for converting an input intensity value into a multi-level pixel value for a halftone cell, a method for specifying matrix values used as modulation levels for converting said intensity value, comprising the steps of:
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a. generating a plurality of transfer functions being mean preserving such that the sum of the derivatives of said transfer functions equals a number of pixel values in said halftone cell; and b. specifying modulation levels from said mean preserving transfer functions. - View Dependent Claims (19, 20, 21, 22)
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Specification