Optical Reader Calibration via LED Drive Current Adjustment
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Solution Overview
Problem
Optical reader systems face challenges in maintaining a wide linear gray scale dynamic range, leading to potential misinterpretation of markings on lottery playslips, especially when uncalibrated, as they struggle to distinguish dark levels from lighter levels with many gray levels in between.
Innovation Solution
A calibration method using a target with a range of linear gray levels is employed, where light sources and photo-transistors are arranged across a document, and the LED drive current is adjusted to achieve a linear response by averaging digital numbers from adjacent columns, forming bins and analyzing histograms to determine the optimal LED drive current for accurate illumination.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If no calibration is performed, then the system operates with default settings, but the gray scale dynamic range is non-uniform and markings may be misinterpreted
Solution Approach 1:
The patent applies parameter changes by adjusting the LED drive current to an optimized value during calibration. This changes the illumination parameter to achieve a linear response across the gray scale range, transforming the non-uniform gray scale response into a uniform one and enabling accurate marking interpretation.
Solution Approach 2:
The patent replaces manual calibration procedures with an automated calibration process that uses a calibration target and computational algorithms. The system automatically determines the optimal LED drive current by analyzing the response to the calibration target, substituting manual adjustment with an automated measurement and calculation system.
2Illumination intensity
If LED drive current is increased to improve signal strength, then more light is available for scanning, but the linear gray scale dynamic range is reduced
Solution Approach 1:
The patent uses parameter changes by systematically varying the LED drive current during calibration and selecting the specific current value that achieves the desired linear gray scale response. This optimized parameter setting simultaneously provides sufficient illumination intensity while maintaining the linear dynamic range necessary for accurate gray level discrimination.
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
This method ensures a wide linear dynamic range, allowing for accurate interpretation of markings on lottery playslips by calibrating the optical reader system, enhancing its reliability and integrity by maintaining a consistent gray scale response across the document.
Implementation Method 1
Light or photo-sensitive receivers also are distributed along the length of the bar and are positioned to receive light that is reflected from the document as it passes the bar. In this environment, each photo-sensitive receiver represents a pixel and the intensity of the reflected light corresponds to the scene on the document
Implementation Method 2
Illumination is typically provided from light emitting diodes (LEDs) distributed along the length of the bar
Data Source
AI summary
A method and system for calibrating optical reader systems employs a target with areas comprising linear gray scale levels. The gray scale levels include the darkest and the lightest scenes. The gray scale levels are illuminated by an array of LEDs and the light reflected from target impacts photo-transistors. The photo-transistors are biased in their linear ranges and the target is scanned while the LED drive current is changed. The photo-transistor responses to the different gray scale levels at the different LED drive currents are analyzed, and the LED rive current that produces a linear output from the photo-transistors over the gray scale dynamic range is selected. Several video channels may be used and their offsets and gains are normalized. Black offsets and black to white gain correction functions are generated for balancing or correcting each pixel. The correction functions may be applied by a processor for later raw image data of scenes scanned by the optical reader.