Biometric Image Acquisition Compensation Filter
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Solution Overview
Problem
Existing biometric image acquisition systems face challenges in correcting non-homogeneous light intensity distributions due to unknown or variable distances between the light source and the target, leading to suboptimal image analysis performance.
Innovation Solution
A biometric image acquisition assembly with a lighting system that includes a compensation filter with an inverted spatial distribution of transparency, which homogenizes the light intensity before it reaches the target, independent of the target's position or distance, using a pattern of tints etched by photolithography to correct the light beam's intensity distribution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If software correction is applied to acquired images to correct light intensity distribution, then image quality can be improved, but the correction requires knowledge of light beam characteristics and target distance which are often unavailable or variable
Solution Approach 1:
The compensation filter is placed in the illumination path before the light reaches the target, performing the correction action in advance. The filter's transparency distribution is designed to be the inverse of the light beam's intensity distribution, so that when the beam passes through the filter, the intensity is homogenized before illuminating the target area.
Solution Approach 2:
A compensation filter is introduced as an intermediary element between the light source and the target. This filter mediates the light beam by modifying its intensity distribution through its spatially varying transparency, thereby correcting the non-homogeneous illumination without requiring post-processing software correction.
2Measurement precision
If post-processing software correction is used, then light intensity distribution can be corrected, but it requires precise knowledge of target distance from light source which varies in dynamic environments
Solution Approach 1:
The compensation filter performs the correction action in advance, before the light reaches the target. By designing the filter's transparency distribution to be the inverse of the light beam's intensity distribution, the system achieves distance-independent correction, as the filter is positioned at a fixed location in the illumination path.
Solution Approach 2:
The system changes the physical parameter of the light beam (intensity distribution) by passing it through a medium (compensation filter) with spatially varying transparency. This physical correction approach replaces the need for software-based parameter adjustment that would require knowledge of target distance.
3Reliability
If laser light source is used, then coherent and monochromatic light is provided for analysis, but the light beam exhibits non-homogeneous spatial intensity distribution
Solution Approach 1:
The compensation filter applies different local properties (transparency values) at different spatial locations to correct the non-homogeneous intensity distribution. Each region of the filter has a transparency specifically tailored to compensate for the intensity variation at the corresponding region of the light beam.
Solution Approach 2:
The compensation filter utilizes variations in optical density or transparency (analogous to color changes) across its surface to modulate the light beam's intensity distribution. The filter's transparency pattern, created by photolithography, effectively 'colors' different regions with different light transmission properties to achieve homogenization.
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 solution ensures consistent and improved image quality by correcting light intensity homogeneously, enhancing the accuracy of biometric analysis and fraud detection methods, particularly in dynamic environments like airport checkpoints.
Implementation Method 1
the compensation filter has a transparency with a spatial distribution inverted with respect to the spatial distribution of the light intensity at the level of the light beam emitted by the light source, so that the intensity of the light beam is homogenized by its passage through the compensation filter
Data Source
Figure 1~2b
Figure 3
AI summary
The invention relates to a biometric image acquisition system comprising a lighting system for projecting light onto a target area (2) of an individual, said lighting system comprising a light source (1) configured to emit a light beam towards the target area (2) in a direction of illumination, said light beam having a spatial distribution of its light intensity, a compensation filter (5) disposed in the direction of illumination (3) and adapted to compensate for the spatial distribution of the light intensity emitted by the light source (1) towards the target area (2). The invention also relates to a method for manufacturing and using this system.