Contact Image Sensor Layout for Moiré-Free Banknote Scanning
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Solution Overview
Problem
The moiré effect in image captures, particularly when scanning banknotes, leads to reduced reproducibility due to optical interference from periodic structures, causing variations in pixel measurements and inaccurate hue detection, which is exacerbated by skew and scanning phase differences.
Innovation Solution
A device and method utilizing a contact image sensor with a guide device, driving mechanism, and a contact image sensor comprising rod-shaped lenses and in-line pixel arrays, which are time-division multiplexed for illumination and data capture, allowing for moiré-free imaging by controlling light sources and pixel arrays to maintain reproducibility.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional contact image sensors are used to capture banknotes with periodic structures, then the scanning process can be performed, but moiré effects are generated causing reduced measurement reproducibility
Solution Approach 1:
The patent divides the image sensor into multiple separate pixel arrays (first pixel array and second pixel array) that are spatially separated. Each pixel array captures images at different positions, and the control unit processes these segmented images to eliminate moiré effects by comparing and adjusting the capture positions, thereby improving measurement reproducibility while maintaining scanning capability.
2Measurement precision
If the pixel array size is reduced to improve resolution, then finer details can be captured, but the scanning step becomes too large relative to pixel size exacerbating moiré effects
Solution Approach 1:
The patent employs dynamic adjustment of the scanning process through the control unit, which adjusts the scanning step and capture position based on the relationship between pixel array size and scanning step. The system dynamically optimizes the scanning parameters to maintain appropriate ratios between pixel size and scanning step, preventing moiré effects while preserving high resolution capability.
Solution Approach 2:
The control unit receives images from both pixel arrays and processes them with feedback mechanisms to detect and correct moiré patterns. By analyzing the captured images and comparing them against expected patterns, the system adjusts subsequent scanning positions and step sizes to eliminate periodic interference patterns, thereby improving both resolution and scanning precision.
3Reliability
If multiple scanning positions are used to capture images, then moiré effects can be reduced, but the scanning time and complexity increase
Solution Approach 1:
The patent merges the functionality of multiple scanning positions into a single scanning operation by using multiple pixel arrays simultaneously. Instead of sequentially scanning at different positions, both pixel arrays capture images at their respective positions concurrently during a single scan, and the control unit combines these images to achieve moiré-free results, thereby reducing scanning time while maintaining reproducibility.
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
The solution achieves moiré-free imaging, improves reproducibility by reducing variations in pixel measurements, enhances signal-to-noise ratio, and ensures consistent imaging regardless of skew or scanning location, enabling accurate detection of fine structures on banknotes.
Implementation Method 1
at least one light-sensitive in-line pixel array (7) of a contact image sensor arranged in the image plane (5)
Implementation Method 2
a plurality of rod-shaped lenses (6) arranged between the object plane (1a) and the image plane (5)
Data Source
AI summary
A device and method for improving the reproducibility of image captures are provided. The device comprises a guide device (1) configured to guide at least one object (2) in an object plane (1a); at least one driving device (3) configured to transport the object (2) in the object plane (1a) in a transport direction (8); an image plane (5); at least one contact image sensor comprising at least one light source (4) for illuminating the object (2); a plurality of rod-shaped lenses (6) arranged between the object plane (1a) and the image plane (5) and in a row along a direction transverse to the transport direction (8) of the object (2); and at least one light-sensitive in-line pixel array (7) arranged in the image plane (5); a control device (9) configured to control at least one of the light source (4) and the light-sensitive in-line pixel array (7) and to capture a signal generated by the light-sensitive in-line pixel array (7). A light emitted from the light source (4) may be at least partially scattered by the object (2) toward the rod-shaped lenses (6), imaged by means of the rod-shaped lenses (6), and incident on at least a region of the light-sensitive in-line pixel array (7). The photosensitive in-line pixel array (7) may comprise a plurality of one-dimensional in-line pixel arrays (7a, 7b), each extending along the direction transverse to the transport direction (8) of the object (2), arranged parallel to each other and adjacent to each other. Each in-line pixel array (7a, 7b) may comprise a length transverse to the transport direction (8) of the object (2) that completely covers the object (2) to be captured.