Print Image Density Correction for Accurate Defect Inspection
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Solution Overview
Problem
Existing image processing systems struggle to accurately inspect printed matters for defects due to variations in print density caused by changes in the printing apparatus over time, leading to reduced inspection accuracy and increased defective product detection.
Innovation Solution
An image processing device that corrects differences in print image densities using a second difference between a region in the print image and a corresponding region in a reference image, reducing the influence of global density changes by adjusting pixel values based on local average differences and setting threshold limits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If direct comparison between print image and reference image is performed, then inspection process is simple, but inspection accuracy deteriorates due to density variations
Solution Approach 1:
The patent introduces a correction image as an intermediary element between the print image and reference image. This correction image is generated by comparing the print image with the reference image and contains density adjustment information. The correction image is then applied to the reference image to create a corrected reference image that accounts for density variations, enabling accurate defect detection despite changes in print density over time.
2Measurement precision
If calibration is performed frequently to maintain accuracy, then inspection accuracy is improved, but productivity deteriorates due to time loss
Solution Approach 1:
The patent performs calibration actions preliminarily by generating a correction image that captures density variations. Instead of frequent recalibration, the system creates a correction image from the print image and reference image comparison, then applies this correction to the reference image. This preliminary correction approach maintains inspection accuracy without requiring frequent interruption for recalibration, thus preserving productivity.
3Reliability
If density threshold is set strictly to detect all defects, then defect detection is improved, but false positive rate increases due to density variations
Solution Approach 1:
The patent dynamically adjusts the density threshold parameter based on the correction image. Instead of using a fixed strict threshold, the system modifies the threshold according to the density variations captured in the correction image. This adaptive threshold adjustment maintains high defect detection reliability while reducing false positives caused by normal density variations in the print image.
Data Source
AI summary
There is provided with an image processing device. A correcting unit corrects a first difference between a density of a partial region in a print image obtained by scanning a printed matter to be inspected and a density of a region corresponding to the partial region in a reference image using a second difference between a density of a region including the partial region in the print image and a density of a region corresponding to the region including the partial region in the reference image. An inspecting unit inspects the print image based on the corrected first difference.