Apparatus for processing image signal

Claim 2

An image signal processing apparatus for sampling an input signal representing a continuous tone image, in units of picture elements, to produce a bi-level image signal, the apparatus comprising: error memory means for storing accumulated errors at storage positions respectively corresponding to image positions of an object picture element and a plurality of picture elements which have not yet been processed and are positioned adjacent to the periphery of said object picture element; input correction means for adding a level of said input signal, representing the density of said object picture element in said image, to an accumulated error which has been stored during a preceding processing step at said position within said error memory means corresponding to said object picture element, to derive a corrected level as a result of said addition; bi-level conversion means for comparing said corrected level with a predetermined threshold value to thereby determine a bi-level value for said object picture element, and for producing said bi-level value as said bi-level image signal; difference computation means for deriving a bi-­level conversion error which is the difference between said corrected level and said bi-level value determined for said object picture element; apportionment factor generating means having stored therein a plurality of predetermined apportionment factors, for generating a plurality of apportionment factors for apportioning said bi-level conversion error among said plurality of picture elements disposed peripherally adjacent to said object picture element and; error apportionment and updating means for computing respective error apportionment values corresponding to said peripherally adjacent picture elements, based on said bi-level conversion error for said object picture element and said plurality of apportionment factors, adding said error apportionment values to corresponding accumulated errors which have been previously stored in said error memory means at predetermined storage positions corresponding to said peripherally adjacent picture elements, to thereby produce updated accumulated errors, and storing said updated accumulated errors in said error memory means.

Claim 3

An image signal processing apparatus for sampling an input signal representing a continuous tone image, in units of picture elements, to produce a bi-level image signal, the apparatus comprising: error memory means for storing accumulated errors at storage positions respectively corresponding to image positions of an object picture element and a plurality of picture elements which have not yet been processed and are positioned adjacent to the periphery of said object picture element; input correction means for adding a level of said input signal, representing the density of said object picture element in said image, to an accumulated error which has been stored during a preceding processing step at said position within said error memory means corresponding to said object picture element, to derive a corrected level as a result of said addition; bi-level conversion means for comparing said corrected level with a predetermined threshold value to thereby determine a bi-level value for said object picture element, and for producing said bi-level value as said bi-level image signal; difference computation means for deriving a bi-­level conversion error which is the difference between said corrected level and said bi-level value determined for said object picture element; apportionment factor generating means for generating a plurality of apportionment factors for apportioning said bi-level conversion error among a plurality of picture elements which have not yet been processed and are positioned at the periphery of said object picture element, said apportionment factor generating means functioning to store a single predetermined set of apportionment factors and to generate said apportionment factors by establishing and periodically altering respective correspondences between positions of said plurality of unprocessed peripheral picture elements and respective coefficients of said set of apportionment factors, said alterations being executed with a predetermined period and; error apportionment and updating means for computing respective error apportionment values corresponding to said peripherally adjacent picture elements, based on said bi-level conversion error for said object picture element and said plurality of apportionment factors, adding said said error apportionment values to corresponding accumulated errors which have been previously stored in said error memory means at predetermined storage positions corresponding to said peripherally adjacent picture elements, to thereby produce updated accumulated errors, and storing said updated accumulated errors in said error memory means.

Claim 4

An image signal processing apparatus for sampling an input signal representing a continuous tone image, in units of picture elements, to produce a bi-level image signal, the apparatus comprising: error memory means for storing accumulated errors at storage positions respectively corresponding to image positions of an object picture element and a plurality of picture elements which have not yet been processed and are positioned adjacent to the periphery of said object picture element; input correction means for adding a level of said input signal, representing the density of said object picture element in said image, to an accumulated error which has been stored during a preceding processing step at said position within said error memory means corresponding to said object picture element, to derive a corrected level as a result of said addition; bi-level conversion means for comparing said corrected level with a predetermined threshold value to thereby determine a bi-level value for said object picture element, and for producing said bi-level value as said bi-level image signal; difference computation means for deriving a bi-­level conversion error which is the difference between said corrected level and said bi-level value determined for said object picture element; apportionment factor generating means for generating a plurality of apportionment factors for apportioning said bi-level conversion error among a plurality of picture elements which have not yet been processed and are positioned at the periphery of said object picture element, said apportionment factor generating means functioning to store a single predetermined set of apportionment factors and to generate said apportionment factors by establishing and periodically altering respective correspondences between positions of said plurality of unprocessed peripheral picture elements and respective coefficients of said set of apportionment factors, said alterations being executed with a predetermined period and; error apportionment and updating means for computing respective error apportionment values corresponding to said peripherally adjacent picture elements, based on said bi-level conversion error for said object picture element and said plurality of apportionment factors, adding said said error apportionment values to corresponding accumulated errors which have been previously stored in said error memory means at predetermined storage positions corresponding to said peripherally adjacent picture elements, to thereby produce updated accumulated errors, and storing said updated accumulated errors in said error memory means.

Claim 5

An image signal processing apparatus according to claim 2, in which said apportionment factor generating means (10) comprises a recirculating shift register having a number of stages corresponding to said predetermined set of apportionment factors and responsive to a periodically generated shift signal for executing shift operations, said apportionment factors being respectively held in and periodically shifted through said shift register stages and said apportionment factors being generated as outputs from said shift register stages.

Claim 6

An image signal processing apparatus for sampling an input signal representing a continuous tone image, in units of picture elements, to produce a bi-level image signal, the apparatus comprising: error memory means for storing accumulated errors at storage positions respectively corresponding to image positions of an object picture element and a plurality of picture elements which are disposed at predetermined positions peripherally adjacent to said object picture element in said image; input correction means for adding a level of said input signal, representing the density of said object picture element in said image, to an accumulated error which has been stored during a preceding processing step at said position within said error memory means corresponding to said object picture element, to derive a corrected level as a result of said addition; bi-level conversion means for comparing said corrected level with a predetermined threshold value to thereby determine a bi-level value for said object picture element, and for producing said bi-level value as said bi-level image signal; difference computation means for deriving a bi-­level conversion error which is the difference between said corrected level and said bi-level value determined for said object picture element; apportionment factor generating means for generating apportionment factors for apportioning said bi-level error among said plurality of peripherally adjacent picture elements, said apportionment factors being generated by selection from a plurality of predetermined sets of apportionment factors, said selection being executed periodically with a predetermined alteration period and; error apportionment and updating means for computing respective error apportionment values corresponding to said peripherally adjacent picture elements, based on said bi-level conversion error for said object picture element and said plurality of apportionment factors, adding said error apportionment values to corresponding accumulated errors which have been previously stored in said error memory means at predetermined storage positions corresponding to said peripherally adjacent picture elements, to thereby produce updated accumulated errors, and storing said updated accumulated errors in said error memory means.

Claim 7

An image signal processing apparatus for sampling an input signal representing a continuous tone image, in units of picture elements, to produce a bi-level image signal, the apparatus comprising: error memory means for storing accumulated errors at storage positions respectively corresponding to image positions of an object picture element and a plurality of picture elements which are disposed at predetermined positions peripherally adjacent to said object picture element in said image; input correction means for adding a level of said input signal, representing the density of said object picture element in said image, to an accumulated error which has been stored during a preceding processing step at said position within said error memory means corresponding to said object picture element, to derive a corrected level as a result of said addition; bi-level conversion means for comparing said corrected level with a predetermined threshold value to thereby determine a bi-level value for said object picture element, and for producing said bi-level value as said bi-level image signal; difference computation means for deriving a bi-­level conversion error which is the difference between said corrected level and said bi-level value determined for said object picture element; apportionment factor generating means for generating apportionment factors for apportioning said bi-level error among said plurality of peripherally adjacent picture elements, said apportionment factors being generated by selection from a plurality of predetermined sets of apportionment factors, said selection being executed periodically with a predetermined alteration period and; error apportionment and updating means for computing respective error apportionment values corresponding to said peripherally adjacent picture elements, based on said bi-level conversion error for said object picture element and said plurality of apportionment factors, adding said error apportionment values to corresponding accumulated errors which have been previously stored in said error memory means at predetermined storage positions corresponding to said peripherally adjacent picture elements, to thereby produce updated accumulated errors, and storing said updated accumulated errors in said error memory means.

Claim 8

An image signal processing apparatus according to claim 4, in which said apportionment factor generating means (10) comprises: a plurality of memory means (300, 301) having stored therein respective sets of apportionment factor values; selection signal generating mean (302) for generating a selection signal (307) in accordance with a synchronization signal and; a plurality of selector elements, responsive to said selection signal for sequentially selecting respective ones of said sets of apportionment factors stored in said memory means to be produced as said apportionment factors (K A to K D ) for apportioning said bi-level conversion error among said peripherally adjacent picture elements.

Claim 9

An image signal processing apparatus for sampling an input signal representing a continuous tone image, in units of picture elements, to produce a bi-level image signal, the apparatus comprising: error memory means for storing accumulated errors at storage positions respectively corresponding to image positions of an object picture element and a plurality of picture elements which have not yet been processed and are positioned adjacent to the periphery of said object picture element; input correction means for adding a level of said input signal, representing the density of said object picture element in said image, to an accumulated error which has been stored during a preceding processing step at said position within said error memory means corresponding to said object picture element, to derive a corrected level as a result of said addition; bi-level conversion means for comparing said corrected level with a predetermined threshold value to thereby determine a bi-level value for said object picture element, and for producing said bi-level value as said bi-level image signal; difference computation means for deriving a bi-­level conversion error which is the difference between said corrected level and said bi-level value determined for said object picture element; apportionment factor generating means for generating apportionment factors for apportioning said bi-level error among said plurality of peripherally adjacent picture elements, said apportionment factors being generated by selection from a plurality of predetermined sets of apportionment factors, said selection being executed randomly with a predetermined alteration period and; error apportionment and updating means for computing respective error apportionment values corresponding to said peripherally adjacent picture elements, based on said bi-level conversion error for said object picture element and said plurality of apportionment factors, adding said said error apportionment values to corresponding accumulated errors which have been previously stored in said error memory means at predetermined storage positions corresponding to said peripherally adjacent picture elements, to thereby produce updated accumulated errors, and storing said updated accumulated errors in said error memory means.

Claim 10

An image signal processing apparatus for sampling an input signal representing a continuous tone image, in units of picture elements, to produce a bi-level image signal, the apparatus comprising: error memory means for storing accumulated errors at storage positions respectively corresponding to image positions of an object picture element and a plurality of picture elements which have not yet been processed and are positioned adjacent to the periphery of said object picture element; input correction means for adding a level of said input signal, representing the density of said object picture element in said image, to an accumulated error which has been stored during a preceding processing step at said position within said error memory means corresponding to said object picture element, to derive a corrected level as a result of said addition; bi-level conversion means for comparing said corrected level with a predetermined threshold value to thereby determine a bi-level value for said object picture element, and for producing said bi-level value as said bi-level image signal; difference computation means for deriving a bi-­level conversion error which is the difference between said corrected level and said bi-level value determined for said object picture element; apportionment factor generating means for generating apportionment factors for apportioning said bi-level error among said plurality of peripherally adjacent picture elements, said apportionment factors being generated by selection from a plurality of predetermined sets of apportionment factors, said selection being executed randomly with a predetermined alteration period and; error apportionment and updating means for computing respective error apportionment values corresponding to said peripherally adjacent picture elements, based on said bi-level conversion error for said object picture element and said plurality of apportionment factors, adding said said error apportionment values to corresponding accumulated errors which have been previously stored in said error memory means at predetermined storage positions corresponding to said peripherally adjacent picture elements, to thereby produce updated accumulated errors, and storing said updated accumulated errors in said error memory means.

Claim 11

An image signal processing apparatus according to claim 6, in which said apportionment factor generating means (10) comprises: a plurality of memory means (300, 301) having stored therein respective sets of apportionment factor values; selection signal generating means (302) for generating a selection signal (307) in accordance with a synchronization signal, for random selection of the contents of said memory means and; a plurality of selector means (303 to 306) responsive to said selection signal for randomly selecting respective ones of said sets of apportionment factors stored in said memory means to be produced as said apportionment factors (K A to K D ) for apportioning said bi-level conversion error among said peripherally adjacent picture elements.

Claim 12

An image signal processing apparatus according to claim 7, in which said selection signal generating means (302) comprises a maximum length counter circuit.

Claim 13

An image signal processing apparatus for sampling an input signal representing a continuous tone image, in units of picture elements, to produce a bi-level image signal, the apparatus comprising: error memory means for storing accumulated errors at storage positions respectively corresponding to image positions of an object picture element and a plurality of picture elements which have not yet been processed and are positioned adjacent to the periphery of said object picture element; input correction means for adding a level of said input signal, representing the density of said object picture element in said image, to an accumulated error which has been stored during a preceding processing step at said position within said error memory means corresponding to said object picture element, to derive a corrected level as a result of said addition; bi-level conversion means for comparing said corrected level with a predetermined threshold value to thereby determine a bi-level value for said object picture element, and for producing said bi-level value as said bi-level image signal; difference computation means for deriving a bi-­level conversion error which is the difference between said corrected level and said bi-level value determined for said object picture element; apportionment factor generating means for generating apportionment factors for apportioning said bi-level error among corresponding ones of said plurality of peripherally adjacent picture elements, said apportionment factors being generated by randomly selecting respective ones of a set of apportionment factors to be established in correspondence with said peripherally adjacent picture elements, said random selection being executed periodically with a predetermined alteration period and; error apportionment and updating means for computing respective error apportionment values corresponding to said peripherally adjacent picture elements, based on said bi-level conversion error for said object picture element and said plurality of apportionment factors, adding said error apportionment values to corresponding accumulated errors which have been previously stored in said error memory means at predetermined storage positions corresponding to said peripherally adjacent picture elements, to thereby produce updated accumulated errors, and storing said updated accumulated errors in said error memory means.

Claim 14

An image signal processing apparatus for sampling an input signal representing a continuous tone image, in units of picture elements, to produce a bi-level image signal, the apparatus comprising: error memory means for storing accumulated errors at storage positions respectively corresponding to image positions of an object picture element and a plurality of picture elements which have not yet been processed and are positioned adjacent to the periphery of said object picture element; input correction means for adding a level of said input signal, representing the density of said object picture element in said image, to an accumulated error which has been stored during a preceding processing step at said position within said error memory means corresponding to said object picture element, to derive a corrected level as a result of said addition; bi-level conversion means for comparing said corrected level with a predetermined threshold value to thereby determine a bi-level value for said object picture element, and for producing said bi-level value as said bi-level image signal; difference computation means for deriving a bi-­level conversion error which is the difference between said corrected level and said bi-level value determined for said object picture element; apportionment factor generating means for generating apportionment factors for apportioning said bi-level error among corresponding ones of said plurality of peripherally adjacent picture elements, said apportionment factors being generated by randomly selecting respective ones of a set of apportionment factors to be established in correspondence with said peripherally adjacent picture elements, said random selection being executed periodically with a predetermined alteration period and; error apportionment and updating means for computing respective error apportionment values corresponding to said peripherally adjacent picture elements, based on said bi-level conversion error for said object picture element and said plurality of apportionment factors, adding said error apportionment values to corresponding accumulated errors which have been previously stored in said error memory means at predetermined storage positions corresponding to said peripherally adjacent picture elements, to thereby produce updated accumulated errors, and storing said updated accumulated errors in said error memory means.

Claim 15

An image signal processing apparatus according to claim 9, in which said apportionment factor generating means (10) comprises: memory means (400) having stored therein said set of apportionment factors (K1 to K4); random signal generating means (401) for generating a selection signal (402) and; selector means (403) coupled to receive said apportionment factors and responsive to said selection signal for randomly altering respective output positions of said selector means to which respective ones of said stored apportionment factors are transferred, said apportionment factors for apportioning said bi-level error among corresponding ones of said plurality of peripherally adjacent picture elements being thereby produced as outputs from said selector means.

Claim 16

An image signal processing apparatus for sampling an input signal representing a continuous tone image, in units of picture elements, to produce a bi-level image signal, the apparatus comprising: error memory means for storing accumulated errors at storage positions respectively corresponding to image positions of an object picture element and a plurality of picture elements which are disposed adjacent to the periphery of said object picture element and have not yet been processed; input correction means for adding a level of said input signal, representing the density of said object picture element in said image, to an accumulated error which has been stored during a preceding processing step at said position within said error memory means corresponding to said object picture element, to derive a corrected level as a result of said addition; bi-level conversion means for comparing said corrected level with a predetermined threshold value to thereby determine a bi-level value for said object picture element, and for producing said bi-level value as said bi-level image signal; difference computation means for deriving a bi-­level conversion error which is the difference between said corrected level and said bi-level value determined for said object picture element; apportionment factor generating means for generating apportionment factors for apportioning said bi-level error among said plurality of peripherally adjacent picture elements which have not yet been processed, said apportionment factors being generated by selection from a plurality of predetermined sets of apportionment factors, said selection being performed periodically with a predetermined period of alteration and in accordance with random number generation which is initiated from an arbitrary initial value once in each of an arbitrary number of successive ones of said scanning lines and; error apportionment and updating means for computing respective error apportionment values corresponding to said peripherally adjacent picture elements, based on said bi-level conversion error for said object picture element and said plurality of apportionment factors, adding said error apportionment values to corresponding accumulated errors which have been previously stored in said error memory means at predetermined storage positions corresponding to said peripherally adjacent picture elements, to thereby produce updated accumulated errors, and storing said updated accumulated errors in said error memory means.

Claim 17

An image signal processing apparatus for sampling an input signal representing a continuous tone image, in units of picture elements, to produce a bi-level image signal, the apparatus comprising: error memory means for storing accumulated errors at storage positions respectively corresponding to image positions of an object picture element and a plurality of picture elements which are disposed adjacent to the periphery of said object picture element and have not yet been processed; input correction means for adding a level of said input signal, representing the density of said object picture element in said image, to an accumulated error which has been stored during a preceding processing step at said position within said error memory means corresponding to said object picture element, to derive a corrected level as a result of said addition; bi-level conversion means for comparing said corrected level with a predetermined threshold value to thereby determine a bi-level value for said object picture element, and for producing said bi-level value as said bi-level image signal; difference computation means for deriving a bi-­level conversion error which is the difference between said corrected level and said bi-level value determined for said object picture element; apportionment factor generating means for generating apportionment factors for apportioning said bi-level error among said plurality of peripherally adjacent picture elements which have not yet been processed, said apportionment factors being generated by selection from a plurality of predetermined sets of apportionment factors, said selection being performed periodically with a predetermined period of alteration and in accordance with random number generation which is initiated from an arbitrary initial value once in each of an arbitrary number of successive ones of said scanning lines and; error apportionment and updating means for computing respective error apportionment values corresponding to said peripherally adjacent picture elements, based on said bi-level conversion error for said object picture element and said plurality of apportionment factors, adding said error apportionment values to corresponding accumulated errors which have been previously stored in said error memory means at predetermined storage positions corresponding to said peripherally adjacent picture elements, to thereby produce updated accumulated errors, and storing said updated accumulated errors in said error memory means.

Claim 18

An image signal processing apparatus according to claim 11, in which said arbitrary initial value is a value which is incremented by a predetermined integer once in each of an arbitrary number of successive ones of said scanning lines.

Claim 19

An image signal processing apparatus according to claim 12, in which said apportionment factor generating means (10) comprises: a plurality of memory means (500, 501) having stored therein respective predetermined sets of apportionment factors (ka1 to k1d), (k2a to k2d); an initial value table (502) containing predetermined initial values; random signal generating means (506) coupled to receive an initial value from said initial value table once in each of an arbitrary number of said scanning lines, and to receive a periodically generated sync signal, for generating a selection signal in response to said sync signal based on random number generation which is initiated from said initial value and; a plurality of selector means (508 to 511) responsive to said selection signal for selectively coupling output terminals thereof to receive respective ones of said sets of stored apportionment factors, for thereby producing from said output terminals said apportionment factors for apportioning said bi-level error among corresponding ones of said plurality of peripherally adjacent picture elements.