Image Forming Apparatus Sensor Shading Correction

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Solution Overview

Problem

Existing color adjustment techniques for inkjet printers face challenges in accurately correcting for sensor reading variations, leading to density unevenness due to differences in sensor and illumination characteristics, particularly when dealing with chromatic colors, which can result in reduced color accuracy and increased high-frequency density unevenness.

Innovation Solution

The proposed solution involves an image forming apparatus that includes a printing unit, an image processing unit, a first generation unit for generating color adjustment information based on scanned data, and a second generation unit for generating scan correction information using colorimetric data. This apparatus performs color adjustment processing on a target chart before printing, using both scanned data and colorimetric data to correct for sensor reading characteristics, thereby reducing density unevenness and improving color accuracy.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If color adjustment processing is performed using scanned data obtained by reading a test chart, then printing characteristics can be obtained for head shading correction, but sensor reading characteristics cause density unevenness to occur

Engineering Contradiction:

Improveprinting characteristics measurementVSAvoiddensity uniformity

Core Design Contradiction:

Measurement precisionVSManufacturing precision

Solution Approach 1:

A scan correction table is introduced as an intermediary component to mediate between the scan unit's reading characteristics and the color adjustment processing. The table stores correction values that compensate for sensor variations, allowing the system to use scanned data for color adjustment without suffering from sensor-induced density unevenness.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The scan correction table is generated in advance through preliminary calibration processing before actual color adjustment operations. This preliminary action characterizes the scan unit's reading characteristics and prepares correction data, enabling subsequent color adjustment processing to proceed without density unevenness issues.

Inventive Principle:

Principle #10Preliminary action

2Ease of manufacture

If calibration of illumination and sensor is performed with reference to a white reflection standard, then sensor reading characteristics can be obtained, but variations of sensor reading characteristics remain when spectral characteristics differ from the white reflection standard

Engineering Contradiction:

Improvecalibration process simplicityVSAvoidsensor reading accuracy

Core Design Contradiction:

Ease of manufactureVSMeasurement precision

Solution Approach 1:

The system changes the approach from using a single white reflection standard to using a scan correction table that accounts for various spectral characteristics. This parameter change allows the system to maintain measurement precision across different color conditions while keeping the calibration process relatively simple through automated table generation.

Inventive Principle:

Principle #35Parameter changes

3Reliability

If both scanned data and colorimetric data are utilized for color adjustment, then comprehensive correction can be achieved, but high-frequency density unevenness occurs due to different color spaces and resolutions

Engineering Contradiction:

Improvecolor adjustment accuracyVSAvoiddensity uniformity

Core Design Contradiction:

ReliabilityVSManufacturing precision

Solution Approach 1:

The correction process is segmented into two independent components: scan correction (addressing sensor reading characteristics) and color adjustment (addressing printing characteristics). The scan correction table handles sensor variations separately, allowing the color adjustment processing to use both scanned and colorimetric data without the high-frequency density unevenness that would result from combining them directly.

Inventive Principle:

Principle #1Segmentation

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 reduces density unevenness and enhances color accuracy by accounting for sensor reading variations, ensuring consistent color output across the print surface, even when dealing with chromatic colors, by using both scanned and colorimetric data for precise correction.

Implementation Method 1

scanned data obtained by reading a first chart output from the printing unit by a scan unit

Methodology Applied

Scientific EffectReflection: Reflection

Implementation Method 2

colorimetric data obtained by measuring a second chart output from the printing unit by a colorimetry unit

Methodology Applied

Scientific EffectReflection: Reflection

Data Source

PatentUS20240106966A1Image forming apparatus, control method of image forming apparatus, and storage medium

Publication Date: 2024.03.28 CANON KK

AI summary

There is a possibility that the accuracy of color adjustment decreases due to high-frequency density unevenness on a test chart that is used in a case where sensor reading characteristics are obtained. The present disclosure solves this by correction processing (generating a correction table for sensor shading correction processing) of a reading sensor configuring a scan unit after removing high-frequency density unevenness in advance by performing color adjustment processing (head shading correction processing).