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US 8,009,332 B2Granted
Apparatus and methods for two point tone reproduction curve calibration
AssigneeXerox Corporation
InventorsZhen He, Kuangti Ted Cheng
Life of this patent
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Abstract
Systems and methods provide increased accuracy in recalibrating the tone reproduction curve (TRC) for a photoelectric image sensor that senses density values. The sensor outputs sensed density values for tone patches. A recalibrated TRC is calculated from the original TRC, the known densities of the tone patches, and the sensed density values of the tone patches.
Claims19
A method of calibrating an image sensing system, the method comprising the steps of:
- sensing, by a photoelectric sensor, a first set of tone patches having first known densities and outputting first sensed density values;
- generating a first tone reproduction curve based on the first sensed density values and the first known densities, the first tone reproduction curve providing corrected density values for corresponding sensed density values output by the photoelectric sensor;
- storing the first tone reproduction curve in a storage device;
- sensing, by the photoelectric sensor, a second set of tone patches having second known densities and outputting second sensed density values, the second set of tone patches being sensed at a time subsequent to a time when the first set of tone patches was sensed;
- and
- calibrating the first tone reproduction curve to generate a second tone reproduction curve that is a calibrated tone reproduction curve based on the first tone reproduction curve, the second sensed density values, and the second known densities.
3 more elements
An image acquisition device comprising:
- a photoelectric sensor configured to sense a density of a portion of an image and to output sensed density values;
- a storage unit storing a tone reproduction curve that provides a corrected density output corresponding to an input sensed density value;
- and
- a processor configured to produce a calibration correction for the tone reproduction curve from sensed density values zi, i=1 to 2, of two tone patches having known densities, the processor configured to:
- determine difference values Δyi=yi−f(zi), i=1 to 2, where yi is the known density of the ith tone patch of the two tone patches and f(zi) is the corrected density value output by the tone reproduction curve corresponding to the ith sensed density value zi, and
- generate the calibration correction for the tone reproduction curve to be vj=f(vj)+((Δy1−Δy2)/(z1−z2))*(vj−z2)+Δy2 where yj is the jth corrected density, f(vj) is the tone reproduction curve value corresponding to a jth input sensed density from an image, and vj is the jth sensed density value.
3 more elements
An image acquisition device calibration system comprising:
- a photoelectric sensor configured to sense a density of a portion of an image and to output sensed density values;
- a storage unit storing a first tone reproduction curve that provides a corrected density output corresponding to a sensed density value sensed by the photoelectric sensor;
- and
- a processor configured to:
- sense, using the photoelectric sensor, sensed density values zi, i=1 to m, of a set of (m) calibration tone patches having known densities wi, i=1 to m, and
- calibrate the first tone reproduction curve to generate a second tone reproduction curve that is a calibrated tone reproduction curve based on the first tone reproduction curve, the second sensed density values zi, i=1 to m, and the second known densities wi, i=1 to m.
3 more elements
Dependencies are inferred from the claim text.