Calibrated color scanner with reference level adjustment

Claim 2

A self-calibrating document scanner, comprising A. a detector for generating electric signals indicative of information in a document B. signal processing circuitry connected to receive said detector signals as input and convert said signals to digital form as output for subsequent utilization, said circuitry including first and second adjustment elements for adjusting input-output transfer characteristics of said circuitry, C. means for applying to said signal processing circuitry, in place of said detector signals, first and second internal reference signals, respectively, said signals indicative of first and second reference output levels and driving said circuitry to first and second nominal output levels, respectively, D. means responsive to said nominal output levels for repeatedly varying said adjustment elements until said circuitry provides said first and second reference output levels, respectively.

Claim 3

A document scanner according to claim 1 in which said first adjustment element varies the gain of said processing circuitry.

Claim 4

A document scanner according to claim 1 in which said second adjustment element varies the offset of said processing circuitry.

Claim 5

A document scanner according to claim 1 in which said adjustment elements comprise analog signal transfer elements having at least input terminals and output terminals and responsive to digital signals applied thereto to vary the signal gain between said input and output terminals.

Claim 6

A document scanner according to claim 1 in which said adjustment elements comprise analog signal transfer elements having at least input terminals and output terminals and responsive to digital signals applied thereto to vary the signal offset between said input and output terminals.

Claim 7

A document scanner according to either claim 4 or 5 in which said adjustment elements comprise digital-to-analog converters.

Claim 8

A document scanner according to claim 1 which includes an amplifier connected to receive inputs from said adjustment elements and providing, in conjunction with said elements, a controllable-gain, controllable-offset amplifier.

Claim 9

A document scanner according to claim 7 in which said adjustment elements comprise a first element connected to an amplifying input of said amplifier and a second element connected to an offset-adjusting input of said amplifier, the gain of said first and second elements being adjustable in response to a digital signal applied thereto.

Claim 10

A document scanner according to claim 8 in which said adjustment elements are connected to receive digital words indicative of the gain to which said elements are to be set.

Claim 11

A document scanner according to claim 1 in which the means for varying said adjustment elements includes a controller for determining the difference between said nominal output levels and said reference output levels and applying to said adjustment elements digital signals indicative of said difference.

Claim 12

A document scanner according to claim 1 including (1) means for connecting said detector to said circuitry after said adjustment elements have been adjusted, (2) a first reference band for generating a first reference band output when said band is scanned with said detector, (3) means for adjusting said detector to vary the output thereof in response to an input to drive said first reference band output toward a first reference band reference output in response to scanning said first reference band, (4) a second reference band for generating a second reference band output when said band is scanned with said detector, (5) means for adjusting one of said adjustment elements to drive said second reference band output toward a second reference band reference output in response to scanning said second reference band.

Claim 13

A document scanner according to claim 11 in which said detector comprises a photomultiplier tube connected to a voltage supply and in which the means for adjusting said detector includes means for varying the voltage applied to said tube by said supply.

Claim 14

A document scanner according to claim 11 in which said detector comprises a plurality of photomultiplier tubes responsive to light of different colors, each connected to a voltage supply whose output voltage is controllable in response to inputs applied thereto, and in which the means for adjusting said detector includes means for varying the voltage applied to each said tube by a corresponding voltage supply.

Claim 15

A document scanner according to claim 1 in which said signal processing circuitry further includes: (1) logarithmic amplifying means, (2) means for connecting said logarithmic amplifying means in circuit with signals applied to said signal processing circuitry, (3) means for applying to said signal processing circuitry internal reference signals of equal magnitude and opposite sign, (4) means for repeatedly adjusting a first of said adjustment elements until the outputs provided by said circuitry in response to said equal-magnitude internal reference signals are substantially equal.

Claim 16

A document scanner according to claim 14 which further includes (1) means for applying to said signal processing circuitry internal reference signals of at least three different magnitudes, (2) means for repeatedly adjusting said first adjustment element until the differences in pairs of outputs provided by said circuitry in response to said different magnitude reference signals are substantially equal to the ratios of the magnitudes of corresponding pairs of said signals.

Claim 17

A document scanner according to claim 14 which includes (1) third and fourth adjustment elements, (2) means for supplying to said signal processing circuitry selected internal reference signals indicative of third and fourth reference output levels and driving said circuitry to third and fourth nominal output levels, respectively, (3) means responsive to said nominal output levels for repeatedly varying said third and fourth adjustment elements until said circuitry provides said third and fourth reference output levels, respectively.

Claim 18

A document scanner according to claim 16 which further includes (1) means for connecting said detector to said circuitry after said third and fourth adjustment elements have been adjusted, (2) a first reference band for generating a first reference band output when said band is scanned with said detector, (3) means for adjusting said first adjustment element to drive said first reference band output toward a first reference band reference output in response to scanning said first reference band, (4) a second reference band for generating a second reference band output when said band is scanned with said detector, (5) means for adding internal reference signals of equal magnitude and opposite sign to the output of said detector to form, with said detector output, augmented second reference band outputs, (6) means responsive to said augmented reference band outputs for adjusting said second adjustment element to drive said augmented output toward a second reference band reference output in response to scanning said second reference band.

Claim 19

A self-calibrating document scanner providing both transmissive and reflective scanning, comprising A. a detector for generating electric signals indicative of information in a document B. signal processing circuitry connected to receive said detector signals as input and convert said signals to digital form as output for subsequent utilization, said circuitry including first and second adjustment elements for adjusting input-output transfer characteristics of said circuitry, C. a transparent drum for mounting a document to be scanned, D. first and second reference bands for generating first and second reference band outputs when scanned, E. means for adjusting said adjustment elements in response to scanning said first and second reference bands, respectively, to drive said outputs to first and second reference band reference outputs, respectively.

Claim 20

A self-calibrating document scanner providing both transmissive and reflective scanning, comprising A. a detector for generating electric signals indicative of information in a document B. signal processing circuitry connected to receive said detector signals as input and convert said signals to digital form as output for subsequent utilization, said circuitry including first and second adjustment elements for adjusting input-output transfer characteristics of said circuitry, C. a transparent drum for mounting a document to be scanned, D. first and second reference bands for generating first and second reference band outputs when scanned, E. means for adjusting said adjustment elements in response to scanning said first and second reference bands, respectively, to drive said outputs to first and second reference band reference outputs, respectively.

Claim 21

A document scanner according to claim 18 in which said first reference band comprises a strip of highly light-reflective material positioned for reflection into said detector and backed by a strip of highly light-absorbant material postitioned to block transmission to said detector, said strip providing a reference band maximum signal when said scanner is operated in reflective mode, and providing a reference band minimum signal when said strip is operated in transmissive mode.

Claim 22

A document scanner according to claim 19 in which said second band comprises a longitudinally-extending area formed by the surface of said drum.

Claim 23

A document scanner according to claim 20 in which said first and second reference bands generate "white" and "black" reference level signals, respectively, when scanned in reflective mode, and generate "black" and "white" reference level signals, respectively, when scanned in transmissive mode.

Claim 24

A self-calibrating document scanner providing line-by-line calibration correction, comprising A. a detector for generating electric signals indicative of information in a document, B. signal processing circuitry connected to receive said detector signals as input and convert said signals to digital form as output for subsequent utilization, said circuitry including first and second adjustment elements for adjusting input-output transfer characteristics of said circuitry, C. means for setting each said adjustment element to a reference setting prior to line-by-line scanning of a document, D. first and second reference bands, corresponding to the respective first and second adjustment elements, for generating first and second reference band outputs when said bands are scanned with said detector, E. means for determining, for each adjustment element, a sensitivity factor comprising the ratio of a change in output on successive readings of a corresponding reference band responsive to a change in the corresponding adjustment element from the reference setting of that element, F. means for adjusting, during the scanning of a document, each adjustment element by an amount equal to the product of the sensitivity of said element and the difference between the output corresponding to a reference setting of said adjustment element and the corresponding reference band output during scanning of a line.

Claim 25

A self-calibrating document scanner providing line-by-line calibration correction, comprising A. a detector for generating electric signals indicative of information in a document, B. signal processing circuitry connected to receive said detector signals as input and convert said signals to digital form as output for subsequent utilization, said circuitry including first and second adjustment elements for adjusting input-output transfer characteristics of said circuitry, C. means for setting each said adjustment element to a reference setting prior to line-by-line scanning of a document, D. first and second reference bands, corresponding to the respective first and second adjustment elements, for generating first and second reference band outputs when said bands are scanned with said detector, E. means for determining, for each adjustment element, a sensitivity factor comprising the ratio of a change in output on successive readings of a corresponding reference band responsive to a change in the corresponding adjustment element from the reference setting of that element, F. means for adjusting, during the scanning of a document, each adjustment element by an amount equal to the product of the sensitivity of said element and the difference between the output corresponding to a reference setting of said adjustment element and the corresponding reference band output during scanning of a line.

Claim 26

A document scanner according to claim 22 which further includes means for adding to the detector output corresponding to scanning a second band, prior to determining the sensitivity of said first adjustment element, an internal reference signal providing a reference output corresponding to a defined setting of said second adjustment element.

Claim 29

The method of claim 24 in which said first reference element adjusts the gain of said circuitry.

Claim 30

The method of claim 25 in which said second reference element adjusts the offset of said circuitry.

Claim 31

The method of claim 26 which includes the step of adding an internal offset signal to the output of said detector prior to at least one of said adjustments.

Claim 32

The method of claim 27 which includes the step of adding alternate internal reference signals of equal magnitude and opposite sign to the output of said detector prior to at least one of said adjustments to generate augmented outputs in response thereto, and adjusting said second reference element until said augmented output are equal.