Shading Correction Device Phase Shift Handling Thermal Drift
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Solution Overview
Problem
Existing shading correction techniques in image reading devices face challenges in accurately correcting phase shifts due to thermal environment changes, leading to increased circuit size and inadequate correction of light distribution variations, resulting in noise and streaks in images.
Innovation Solution
A shading correction device and method that includes a first extractor, a second extractor, an intersection point calculator, a phase shift amount calculator, a phase shifter, a generator, and a corrector, which extract and smooth periodic components from original and new shading data, calculate phase shifts, and generate corrected shading data to perform accurate shading correction, reducing circuit size and improving image quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the phase of the periodic component of shading data is shifted with a plurality of different shift amounts to generate multiple periodic components, then the phase shift correction accuracy is improved, but the circuit size increases
Solution Approach 1:
The patent extracts only the necessary periodic component from shading data using a band-pass filter, rather than processing all frequency components. This extraction approach maintains correction accuracy for the lens pitch-related periodic variations while reducing the overall data processing burden and circuit complexity
Solution Approach 2:
Instead of shifting the phase across a full range of possible values, the patent calculates phase shift amount at specific discrete positions (e.g., every 8th or 16th pixel) and uses interpolation to determine phases at intermediate positions. This partial sampling approach achieves sufficient correction accuracy while significantly reducing the number of phase shift calculations required
2Device complexity
If shading correction is performed without accurate phase shift correction, then the circuit size remains small, but noise and streaks appear in the corrected images
Solution Approach 1:
The patent replaces complex mechanical or computational phase alignment mechanisms with a mathematical approach using Fourier transforms and phase shift calculations. This substitution achieves accurate periodic component alignment through signal processing mathematics rather than physical adjustment mechanisms, reducing circuit complexity while eliminating noise and streaks
Solution Approach 2:
The patent introduces an intermediary phase shift amount calculation step that bridges the original shading data and the corrected shading data. By calculating the phase shift amount as an intermediate parameter and using it to adjust the periodic component, the system achieves accurate correction without requiring direct complex comparison of multiple shifted versions
3Adaptability or versatility
If the thermal environment changes between manufacturing process and document reading, then the phase of periodic component shifts, but typical shading correction techniques cannot accurately correct this shift
Solution Approach 1:
The patent performs preliminary extraction of the periodic component from shading data obtained during the manufacturing process at a reference temperature. By pre-processing the shading data to isolate the periodic component related to lens pitch, the system creates a baseline that can be systematically adjusted for thermal variations during actual document reading, improving adaptability while maintaining precision
Solution Approach 2:
The patent systematically varies the phase shift parameter to find the optimal alignment between periodic components from different thermal conditions. By changing the phase shift parameter in controlled increments and evaluating the correlation between original and shifted periodic components, the system adapts to thermal environment changes while maintaining accurate shading correction
Data Source
AI summary
A shading correction device includes first and second extractors, an intersection calculator, a phase shift amount calculator, a phase shifter, a generator, and a corrector. The first extractor extracts a first periodic component of original shading data. The second extractor extracts a second periodic component of a second reading result. The intersection calculator calculates a first intersection of the first component and a reference level and a second intersection of the second component and the reference level. The phase shift amount calculator calculates a phase shift amount at each of plural positions with a difference between the first and second intersections. The phase shifter shifts a phase of the first component with the phase shift amount. The generator generates corrected shading data including the phase-shifted first component and the original shading data with the first component smoothed. The corrector performs shading correction based on the corrected shading data.