Tone Correction Using Luminance Variation of White Area

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Solution Overview

Problem

Conventional electrophotographic apparatuses face accuracy issues in calibration due to surface irregularities in paper, leading to erroneous signal values and decreased calibration accuracy when using scanners with a single illumination source, which generates shadows and affects the paper white portion signal values.

Innovation Solution

An image forming apparatus that outputs a tone chart, reads it, determines the variance of the white area's luminance, corrects luminance values based on surface irregularity influence, and performs tone correction using a tone correction unit to estimate intrinsic signal values, thereby preventing accuracy decreases in calibration.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Device complexity

If a scanner with a single illumination source is used to read the tone chart, then the device complexity is reduced, but measurement precision deteriorates due to shadow generation from surface irregularities

Engineering Contradiction:

Improvescanner structureVSAvoidsignal value accuracy

Core Design Contradiction:

Device complexityVSMeasurement precision

Solution Approach 1:

The patent applies preliminary action by detecting surface irregularities and correcting luminance values before performing tone correction. The system reads the tone chart, detects surface irregularities in the white area, corrects luminance values based on detected irregularities, and then performs tone correction using the corrected values, preventing shadow-induced errors from affecting calibration accuracy

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The patent applies parameter changes by adjusting luminance values based on detected surface irregularities. The system changes the luminance parameter of the white area in the tone chart to compensate for shadow effects, enabling accurate tone correction despite using a single illumination source

Inventive Principle:

Principle #35Parameter changes

2Adaptability or versatility

If paper with large surface irregularities is used in calibration, then the adaptability of the calibration process is improved, but measurement precision deteriorates due to shadow generation affecting paper white portion signal values

Engineering Contradiction:

Improvecalibration process adaptabilityVSAvoidpaper white signal value accuracy

Core Design Contradiction:

Adaptability or versatilityVSMeasurement precision

Solution Approach 1:

The system performs preliminary detection of surface irregularities in the paper white area before conducting tone correction. By detecting irregularities first and correcting luminance values based on the detection results, the system prepares the data in advance to eliminate shadow effects, ensuring accurate calibration even with papers having large surface irregularities

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The patent creates a corrected version of the tone chart data by copying and adjusting luminance values. The system generates corrected luminance values that represent what the paper white portion would look like without surface irregularities, enabling accurate calibration despite the physical imperfections of the paper

Inventive Principle:

Principle #26Copying

Data Source

PatentUS11265447B2Utilizing luminance variation of the white area of the tone chart in tone correction

Publication Date: 2022.03.01 CANON KK

AI summary

An image forming apparatus outputs a tone chart for calibration by a printer, reads the output tone chart by a scanner, determines whether data on a sheet is affected by a surface shape of the sheet based on the read tone chart, corrects data on a white area of the read chart based on a result of the determination, and executes calibration using the corrected data.