Fixed Pattern Noise Compensation in Optical Data Readers
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Solution Overview
Problem
Optical data readers face significant performance limitations due to fixed pattern noise (FPN), particularly in low light conditions, which can be costly to mitigate through component selection or calibration, and existing methods either require additional resources or are inefficient in reducing noise sources like dark current and pixel response non-uniformity.
Innovation Solution
The method involves capturing dark and illuminated images with different exposure times, subtracting the dark image from the illuminated image to compensate for FPN, and using virtual scan lines to reduce noise, allowing for partial compensation of FPN during normal operation without the need for extensive calibration or expensive components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If FPN compensation methods are used to improve signal-to-noise ratio, then measurement precision is improved, but device complexity increases due to additional calibration procedures and processing steps
Solution Approach 1:
The system performs preliminary actions by capturing dark images and calculating FPN compensation data before actual barcode reading operations. The FPN compensation data is pre-calculated and stored, allowing rapid compensation during normal operation without extensive real-time calibration, thus improving signal-to-noise ratio while limiting complexity increase.
Solution Approach 2:
The patent extracts the FPN compensation function as a separate, independent process. By isolating the FPN calculation and compensation steps from the main barcode reading workflow, the system can apply precision improvements without significantly complicating the core device operations. The FPN data is extracted and stored separately for later application.
2Measurement precision
If longer exposure times are used to reduce noise, then measurement precision is improved, but productivity decreases due to slower reading speeds
Solution Approach 1:
The system changes the parameter approach by using FPN compensation data derived from dark images with different exposure times to create a corrected reading from a standard exposure time image. This allows the system to achieve noise reduction benefits without actually using longer exposure times during normal operation, thus maintaining productivity while improving measurement precision.
3Measurement precision
If expensive low-noise components are used to reduce FPN, then measurement precision is improved, but device cost increases
Solution Approach 1:
The system implements self-service by having the image sensor itself provide the data needed for FPN compensation. The dark images are captured using the same sensor that will be used for barcode reading, and the FPN compensation data is derived from the sensor's own characteristics. This eliminates the need for expensive external calibration equipment or specialized low-noise components, improving measurement precision while keeping device cost low.
4Measurement precision
If multiple dark images are captured to estimate different FPN components, then measurement precision is improved, but loss of time increases due to additional image captures
Solution Approach 1:
The system performs the multi-image FPN characterization as a preliminary action during manufacturing or initial setup, separate from normal operation. By completing the time-consuming multiple image captures and FPN component estimation beforehand, the system achieves high measurement precision during actual barcode reading without incurring time losses during productive operations. The FPN compensation data is stored for rapid application during normal use.
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 approach improves the signal-to-noise ratio, enables faster exposure times, and reduces the cost of optical data readers by effectively mitigating FPN, especially in low light conditions, without requiring extensive calibration or expensive components.
Implementation Method 1
A detector generates an electrical signal that has an amplitude determined by the intensity of the collected light
Data Source
AI summary
This disclosure relates generally to systems and methods for estimating and, at least partially, compensating for fixed pattern noise (FPN) in an image sensor. In one configuration, an estimate of the FPN of an image sensor may be obtained by capturing a dark image (either a linear or an area image, depending on the sensor type) using a first exposure time, an illuminated image may be captured using a second exposure time, the second exposure time is greater than the first exposure time, and the dark image may be subtracted from the illuminated image to compensate, at least partially, for FPN. Certain configurations may utilize virtual scan lines. Two or more dark images may also be utilized to estimate FPN in an image sensor.