Color Calibration Using External Colorimeter and Reference Document

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Solution Overview

Problem

Image forming apparatuses face challenges in achieving high-quality color printing due to individual differences in light source chromaticity and color filter layer thickness, affecting color calibration and resulting in color fluctuations.

Innovation Solution

An image forming apparatus that uses a reference document generated with CMY inks and an external colorimeter to perform color calibration by setting correction coefficients based on spectral reflectance, converting RGB gradation values to device-independent values, and generating a color profile to align the color of the reference document and toner images.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If color calibration is performed using image reading unit with light source and color filter, then color reproduction is achieved, but individual differences in light source chromaticity and color filter layer thickness cause color fluctuations

Engineering Contradiction:

Improvecolor calibration accuracyVSAvoidcolor consistency

Core Design Contradiction:

Measurement precisionVSReliability

Solution Approach 1:

The patent introduces an external colorimeter as an intermediary measurement device that is independent of the image reading unit's light source and color filter. This colorimeter provides objective color data that is not affected by individual differences in the image reading unit, serving as a mediator to establish accurate color profiles that compensate for the variability in the imaging system.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The patent creates a color profile that copies or maps the relationship between the image reading unit's RGB values and the colorimeter's device-independent color values. This profile acts as a transfer function that replicates the color characteristics of the reference document, allowing the system to compensate for individual differences by referencing the standardized color measurements.

Inventive Principle:

Principle #26Copying

2Manufacturing precision

If spectral reflectance measurement is used to set correction coefficient, then color accuracy between reference document and toner image is improved, but measurement and processing complexity increases

Engineering Contradiction:

Improvecolor matching accuracyVSAvoidcalibration system complexity

Core Design Contradiction:

Manufacturing precisionVSDevice complexity

Solution Approach 1:

The patent replaces complex mechanical measurement systems with a simplified approach using an external colorimeter that directly measures color properties. Instead of using multiple sensors and complex optical paths to measure spectral reflectance, the system uses a dedicated color measurement device that provides the necessary color data through a single, streamlined measurement process.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The patent transforms the calibration approach by changing from direct spectral reflectance measurement to using device-independent color values (such as L*a*b*) as intermediaries. This parameter transformation simplifies the correction process by working with perceptually uniform color spaces where the correction coefficient can be more effectively applied to achieve accurate color matching between the reference document and toner image.

Inventive Principle:

Principle #35Parameter changes

Applied Scientific Principles

This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.

Function Achieved in This Case

This approach effectively suppresses individual differences in color reproduction, improving the accuracy and consistency of color printing by generating a color profile that corrects for variations in light source chromaticity and color filter thickness.

Implementation Method 1

The image reading unit 100 reads an image on a document D and generates image data ID

Methodology Applied

Scientific EffectPhotoelectric Effect: Photoelectric Effect

Implementation Method 2

a spectral reflectance of the reference document in a visible band and a spectral reflectance in the visible band of the toner image

Methodology Applied

Scientific EffectSpectral Reflectance: Reflection

Data Source

PatentUS11310394B2Image forming apparatus, image forming method, and computer-readable non-transitory recording medium storing image forming program, for performing color cailibration by using reference

Publication Date: 2022.04.19 KYOCERA DOCUMENT SOLUTIONS INC

AI summary

An image forming apparatus can perform color calibration by using a reference document generated with use of ink and an external colorimeter. An image reading unit reads an image on a document and generates image data. An image forming unit forms an image on an image forming medium by using CMY toners. A color calibration processing unit sets a correction coefficient by using a spectral reflectance of the reference document in a visible band, and a spectral reflectance in the visible band of a toner image formed on the image forming medium with use of toner. The color calibration processing unit also performs correction by multiplying the correction coefficient with a gradation value of each of RGB, generates a conversion formula from the each gradation value of RGB to each device-independent value, and generates a color profile by using the conversion formula.