Optical Structure for Fingerprint Image Distortion Correction
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Solution Overview
Problem
Conventional optical fingerprint acquisition devices suffer from keystone distortion due to inherent optical properties, requiring costly optical correction units or time-consuming software calculations, which can degrade optical performance and are not effective for precise distortion correction.
Innovation Solution
An optical structure comprising a prism, a lighting unit, a reflector unit, and a lens unit with a concave mirror and eccentrically aligned lenses to correct geometric distortion, combined with simple software processing for image magnification adjustment, minimizing overall system size and maintaining optical performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If an optical correction unit is added between the prism and image sensor, then distortion correction is improved, but device complexity and cost increase
Solution Approach 1:
The patent extracts the distortion correction function from a separate optical correction unit and integrates it into the prism structure itself by tilting the image sensor at a specific angle. This eliminates the need for additional optical correction components while achieving the same distortion correction effect.
Solution Approach 2:
The patent uses software processing to create a virtual correction of the fingerprint image, effectively copying the correction function without requiring physical optical correction elements. The software algorithm compensates for distortion by processing the captured image data.
2Measurement precision
If the image sensor is tilted for distortion correction, then distortion is reduced, but manufacturing precision requirements increase
Solution Approach 1:
The patent changes the orientation parameter of the image sensor by tilting it at a specific angle relative to the prism. This parameter change enables the sensor to capture the fingerprint image with minimal distortion while working around the optical limitations of the prism structure.
3Reliability
If software distortion correction is used, then optical performance is maintained, but processing time increases
Solution Approach 1:
The patent performs preliminary optical distortion correction by tilting the image sensor during the capture process, so that the majority of distortion is eliminated before software processing is needed. This preliminary action reduces the computational burden and processing time required for subsequent software correction.
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 high-resolution fingerprint acquisition with minimal distortion, enabling real-time processing of fingerprint images without image distortion, even for rolled or consecutive fingerprints, while maintaining optical performance and reducing product size.
Implementation Method 1
in an optical fingerprint optical system including a total internal reflection prism
Implementation Method 2
a lens unit configured to comprise two or more lenses, each being configured to receive the fingerprint image reflected from the reflector unit
Data Source
AI summary
An optical structure for acquiring a fingerprint image with high resolution and minimum distortion is provided. The optical structure includes a prism configured to comprise an input surface to which light is irradiated, a contact surface formed horizontally to be in contact with a finger, and an output surface through which the light that has been irradiated to the input surface and reflected from the finger in contact with the contact surface passes; a lighting unit configured to emit a beam to the input surface of the prism; a reflector unit configured to reflect a fingerprint image passing through the output surface of the prism; a lens unit configured to comprise two or more lenses, each being configured to receive the fingerprint image reflected from the reflector unit; and an image sensor on which the fingerprint image passing through the lens unit is formed.