Moist Fingerprint Imaging Prism Angle Optimization
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Solution Overview
Problem
Conventional fingerprint capturing devices fail to produce high-quality images when the finger is wet or moist, due to artifacts that degrade the captured image, particularly resulting in bridging between adjacent ridges.
Innovation Solution
An apparatus featuring a prism with an imaging plane, a bottom plane parallel to the imaging plane, and a reflective plane intercepting both at an angle α greater than 45° + (arc sin(n1/n2))/2, where n1 is the refractive index of the medium between the finger's valleys and the imaging plane, and n2 is the refractive index of the prism, along with a light source and lens to capture reflected light, optimizing the angle for improved contrast and artifact reduction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional fingerprint capturing devices are used with a moist finger, then the imaging process is simple, but the image quality degrades due to artifacts and bridging between adjacent ridges
Solution Approach 1:
The apparatus divides the imaging function into separate components: a light source positioned at a specific angle, a prism with controlled geometry, and a detector arranged to receive light at a specific observation angle. This segmentation allows each component to be optimized independently for handling moist fingerprints while maintaining overall system functionality.
Solution Approach 2:
The patent changes the critical parameters of the imaging system: the light incident angle is set to a specific value, the observation angle is controlled to be greater than the critical angle, and the prism geometry is optimized. These parameter changes enable the system to eliminate moisture-induced artifacts while preserving ridge-valley contrast.
2Measurement precision
If the angle of observation is increased to reduce moisture artifacts, then image quality improves, but the device complexity increases due to precise angular requirements
Solution Approach 1:
The prism is designed with specific geometric angles that create equipotential optical paths, ensuring that light rays traveling through the prism maintain consistent angular relationships. This geometric design inherently satisfies the angular precision requirements without requiring active control mechanisms.
Solution Approach 2:
The prism acts as an intermediary optical element that mediates between the light source and the detector. It transforms the light paths to achieve the required observation angle greater than the critical angle, thereby reducing moisture artifacts while simplifying the overall angular alignment requirements.
3Measurement precision
If the light incident angle is adjusted to optimize ridge-valley contrast, then image contrast improves, but the device complexity increases due to precise positioning requirements
Solution Approach 1:
The light source and its positioning mechanism are merged with the prism structure. The light source is positioned at a specific angle relative to the prism faces, and this arrangement is integrated into the overall device design, eliminating the need for separate adjustment mechanisms.
Solution Approach 2:
The prism geometry itself provides the necessary angular relationships for optimal imaging. The fixed angles of the prism automatically ensure that light incident at the correct angle will be reflected to the detector at the correct observation angle, making the system self-aligning and reducing positioning complexity.
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 apparatus produces high-quality images with enhanced contrast and reduced artifacts from moisture, achieving better image quality by controlling the angle of incidence and reflection to separate and clearly capture ridge and valley features.
Implementation Method 1
a light source for generating a light with an incident angle of approximately 0° with respect to a surface normal of the imaging plane
Implementation Method 2
a reflective plane intercepting the imaging plane and intercepting the bottom plane at an angle α; and a lens for capturing light reflected from the reflective plane
Implementation Method 3
a lens for capturing light reflected from the reflective plane
Implementation Method 4
an image sensor for generating an image of the valleys and ridges of the finger
Data Source
AI summary
An apparatus for capturing the image of a wet/moist fingerprint. The apparatus includes: a prism having an imaging plane on which a finger having valleys and ridges is place, a bottom plane parallel to the imaging plane and a reflective plane intercepting the imaging plane and intercepting the bottom plane at an angle α; a light source for generating a light with an incident angle of approximately 0° with respect to a surface normal of the imaging plane; and a lens for capturing light reflected from the reflective plane. The apparatus further includes an image sensor for generating an image of the valleys and ridges of the finger, wherein the reflective plane is arranged in such a way to meet the equation of α>45 +(arc sin (n1/n2))/2, where n1 is a refraction index of medium filled between the valleys of the finger and the imaging plane, and n2 is refraction index of the prism.