Dynamic discrimination reference level generator for a parallel channel optical document scanner

Claim 2

A discrimination function generator for generating a plurality of variable discrimination reference level signals in a character recognition system wherein a character bearing document is simultaneously scanned by a plurality of light sensing devices to produce a corresponding plurality of video signals having magnitudes indicative of the light reflectance of individual linearly adjacent areas of the document, each area corresponding to a different one of said light sensing devices, comprising: a. a plurality of stages each adapted to generate a variable discrimination reference level signal for a predetermined one of said video signals, and each of said stages being connected to a predetermined set of said light sensing devices such that each discrimination reference level signal varies as a function of the magnitudes of a predetermined set of said video signals derived from document areas adjacent the document area corresponding to said one predetermined video signal, each set of video signals including at least one video signal that is common to at least one other set of video signals, b. a plurality of correlation means individually interconnected between adjacent ones of said stages, each correlation means being adapted to increase a discrimination reference level signal whenever it is exceeded by a predetermined amount by an adjacent discrimination reference level signal; and c. a plurality of comparator means, each responsive to said predetermined one video signal and to said discrimination reference level signal of one of said stages for producing a binary-valued output signal indicative of the relative magnitudes of said one predetermined video signal and said discrimination reference level signal.

Claim 3

selecting the maximum one of the two compared signals as the discrimination reference level signal.

Claim 4

selecting the maximum one of the two compared signals as the discrimination reference level signal.

Claim 5

A discrimination function generator as defined in claim 1 wherein each discrimination reference level signal is a function of the magnitude of the maximum video signal in the predetermined set from which each discrimination reference level signal is derived.

Claim 6

A discrimination function generator as defined in claim 2 wherein each video signal is excluded from the predetermined set of video signals from which its discrimination reference level signal is derived.

Claim 7

A discrimination function generator as defined in claim 3 further comprising: a. means for generating a minimum discrimination reference level signal, and b. means for

Claim 8

A discrimination function generator as defined in claim 4 further comprising: a. means for maintaining said minimum reference level signal at a constant level for average and below average character-document contrast, and b. means for increasing the value of said minimum reference level signal for above average character-document contrast.

Claim 9

A discrimination function generator for generating a plurality of variable discrimination reference level signals wherein a document is simultaneously scanned by a plurality of light-sensing devices to produce a corresponding plurality of video signals having magnitudes indicative of the light reflectanCe of individual adjacent areas of the document, each area corresponding to a different one of said light-sensing devices, comprising: a. a plurality of stages each coupled to a predetermined set of said light-sensing devices for generating a variable discrimination reference level signal for one of said video signals, each discrimination reference level signal being a function of the magnitude of the maximum video signal of a predetermined set of video signals derived from document areas adjacent to but excluding the document area corresponding to said one video signal, each set of video signals including a video signal which is common to at least one other set of video signals; b. a plurality of correlation means individually interconnected between adjacent ones of said stages, each correlation means being adapted to increase a discrimination reference level signal whenever it is exceeded by a predetermined amount by an adjacent discrimination reference level signal; c. means for generating a minimum discrimination reference level signal; d. means for (1) comparing the maximum video signal in each set with the minimum discrimination reference level signal, and (2) selecting the larger one of the two compared signals as the discrimination reference level signal; e. means for maintaining said minimum reference level signal at a constant level for average and below-average document contrast; and f. means for increasing the value of said minimum reference level signal for above-average document contrast, wherein said value increasing means comprises a peak video signal detecting circuit responsive to the maximum one of said plurality of video signals for increasing the level of said minimum reference level signal.

Claim 10

A discrimination function generator for generating a plurality of variable discrimination reference level signals wherein a document is simultaneously scanned by a plurality of light-sensing devices to produce a corresponding plurality of video signals having magnitudes indicative of the light reflectanCe of individual adjacent areas of the document, each area corresponding to a different one of said light-sensing devices, comprising: a. a plurality of stages each coupled to a predetermined set of said light-sensing devices for generating a variable discrimination reference level signal for one of said video signals, each discrimination reference level signal being a function of the magnitude of the maximum video signal of a predetermined set of video signals derived from document areas adjacent to but excluding the document area corresponding to said one video signal, each set of video signals including a video signal which is common to at least one other set of video signals; b. a plurality of correlation means individually interconnected between adjacent ones of said stages, each correlation means being adapted to increase a discrimination reference level signal whenever it is exceeded by a predetermined amount by an adjacent discrimination reference level signal; c. means for generating a minimum discrimination reference level signal; d. means for (1) comparing the maximum video signal in each set with the minimum discrimination reference level signal, and (2) selecting the larger one of the two compared signals as the discrimination reference level signal; e. means for maintaining said minimum reference level signal at a constant level for average and below-average document contrast; and f. means for increasing the value of said minimum reference level signal for above-average document contrast, wherein said value increasing means comprises a peak video signal detecting circuit responsive to the maximum one of said plurality of video signals for increasing the level of said minimum reference level signal.

Claim 11

A discrimination function generator as defined in claim 1 wherein said plurality of stages comprises: a. a resistive ladder network comprising a plurality of resistive dividers each corresponding to a different one of said plurality of video signals, and b. means coupling each said set of video signals to a corresponding resistive divider for producing said discrimination reference level signal.

Claim 12

A discrimination function generator for generating a plurality of variable discrimination reference level signals in a system wherein a document is simultaneously scanned by a plurality of light-sensing devices to produce a corresponding plurality of video signals having magnitudes indicative of the light reflectance of individual adjacent areas of the document, each area corresponding to a different one of said light-sensing devices, comprising: a. a plurality of stages each coupled to a predetermined set of said light-sensing devices for generating a variable discrimination reference level signal for a different one of said video signals, each discrimination reference level signal being a function of the magnitudes of a predetermined set of video signals derived from document areas adjacent the document area corresponding to said one video signal, each set of video signals including a video signal which is common to at least one other set of video signals, said plurality of stages including a resistive ladder network having a plurality of resistive dividers each corresponding to a different one of said plurality of video signals, and means coupling each set of video signals to a corresponding resistive divider for producing said discrimination reference level signals; and b. a plurality of correlation means individually interconnected between adjacent ones of said stages, each correlation means being adapted to increase one of said discrimination reference level signals whenever it is exceeded by a predetermined amount by an adjacent discrimination reference level signal, wherein said correlation means comprises a resistor connected between adjacent ones of said resistive dividers, whereby each discrimination reference level signal is increased whenever it is exceeded by an adjacent discrimination reference level Signal.

Claim 13

A discrimination function generator for generating a plurality of variable discrimination reference level signals in a system wherein a document is simultaneously scanned by a plurality of light-sensing devices to produce a corresponding plurality of video signals having magnitudes indicative of the light reflectance of individual adjacent areas of the document, each area corresponding to a different one of said light-sensing devices, comprising: a. a plurality of stages each coupled to a predetermined set of said light-sensing devices for generating a variable discrimination reference level signal for a different one of said video signals, each discrimination reference level signal being a function of the magnitudes of a predetermined set of video signals derived from document areas adjacent the document area corresponding to said one video signal, each set of video signals including a video signal which is common to at least one other set of video signals, said plurality of stages including a resistive ladder network having a plurality of resistive dividers each corresponding to a different one of said plurality of video signals, and means coupling each set of video signals to a corresponding resistive divider for producing said discrimination reference level signals; and b. a plurality of correlation means individually interconnected between adjacent ones of said stages, each correlation means being adapted to increase one of said discrimination reference level signals whenever it is exceeded by a predetermined amount by an adjacent discrimination reference level signal, wherein said correlation means comprises a resistor connected between adjacent ones of said resistive dividers, whereby each discrimination reference level signal is increased whenever it is exceeded by an adjacent discrimination reference level Signal.

Claim 14

A discrimination function generator as defined in claim 8 further comprising a correlation resistor connected between the resistive dividers on opposite ends of said resistive ladder network.