Inspection Apparatus Distortion Correction for Printed Matter
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Solution Overview
Problem
Existing inspection systems face challenges in accurately aligning printed images due to variations in distortion caused by factors like sheet elongation and conveyance unevenness, which are not effectively addressed by current alignment technologies, especially when dealing with different printing conditions such as temperature changes and moisture content.
Innovation Solution
An inspection apparatus and method that reads a chart printed by a printing apparatus to generate distortion information, corrects the inspection target image using this information, and aligns it with a reference image to improve alignment accuracy, employing a two-stage distortion correction process involving free form deformation and control point optimization.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If non-rigid body alignment using free form deformation is used to achieve more accurate alignment including local magnification and positional displacement, then alignment accuracy is improved, but optimization cannot be performed when positional displacement is large and the update position of the control point cannot be obtained
Solution Approach 1:
The patent applies preliminary action by first performing rigid body alignment (translation and rotation) to bring the inspection target image and reference image into rough alignment before attempting free form deformation. This preliminary step ensures that the initial positional displacement is reduced to a manageable level, allowing the subsequent non-rigid body alignment to converge properly and achieve high accuracy without optimization failure.
2Manufacturing precision
If distortion information is used to correct position using a distortion correction chart, then large tendency of distortion can be corrected, but slight variation in distortion for each sheet due to different conditions cannot be coped with
Solution Approach 1:
The patent implements self-service by automatically generating a distortion correction chart from the inspection target image itself rather than requiring a separate pre-prepared chart. The system extracts feature points from the actual printed image, computes the distortion based on the printed data, and generates correction parameters specific to that sheet. This enables each sheet to be corrected according to its individual distortion characteristics caused by variations in fixing temperature, moisture content, and other printing conditions.
3Extent of automation
If RIP data is used as reference image for automatic generation from print data, then advantage in variable printing is obtained, but local distortion due to conveyance unevenness or sheet elongation occurs in the inspection target image that is not present in the reference image
Solution Approach 1:
The patent applies segmentation by dividing the alignment process into two distinct stages: first performing rigid body alignment (translation and rotation) to handle global differences between RIP data and scanned images, then performing free form deformation to correct local distortion. This segmentation allows each alignment method to address specific types of misalignment, achieving both automation and high precision.
Solution Approach 2:
The patent uses parameter changes by transitioning from rigid body transformation parameters (translation vector and rotation angle) to free form deformation parameters (control point displacement fields). This change in alignment parameters enables the system to adapt from handling global image differences to correcting local distortion, resolving the contradiction between using undistorted RIP data as reference and achieving accurate alignment with distorted scanned images.
Data Source
AI summary
The present invention provides an inspection apparatus including a reading unit configured to read a document. The inspection apparatus compares a read image obtained by the reading unit reading a chart including a mark for acquiring distortion information printed by a printing apparatus and a reference image serving as a correct image of the chart, and generates distortion information when reading by the reading unit; and corrects, using the generated distortion information, an inspection target image obtained by the reading unit reading a printed matter from the printing apparatus; aligns the first corrected image corrected in the correcting with a reference image of the printed matter; and compares a second corrected image aligned in the aligning with a reference image of the printed matter to inspect a defect of the printed matter.