Fingerprint Image Construction Using Sub-Pixel Interpolation
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Solution Overview
Problem
Conventional fingerprint image construction techniques using sweep type sensors often result in image distortion due to non-integer pixel pitch movement errors, leading to difficulties in fingerprint collation and increased processing requirements for high resolution sensors.
Innovation Solution
The method involves storing partial images and calculating movement vectors with higher resolution through interpolation and weighted averaging, allowing precise alignment of images regardless of sensor resolution, thereby reducing distortion and improving collation accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the pixel pitch of the fingerprint sensor is made small to reduce movement error, then measurement precision is improved, but device complexity and cost increase due to higher processing requirements
Solution Approach 1:
The patent changes the parameter of movement quantity calculation from direct pixel-based measurement to interpolation-based calculation. By computing movement quantity as a real number through interpolation between adjacent pixels rather than using integer pixel displacements, the system achieves high measurement precision without requiring high-resolution sensors, thus avoiding increased device complexity
Solution Approach 2:
The patent replaces the mechanical approach of using high-resolution physical sensors with a computational approach using interpolation algorithms. Instead of relying on hardware with small pixel pitch, the system uses software-based interpolation to achieve sub-pixel measurement precision, substituting mechanical complexity with computational processing
2Device complexity
If conventional movement quantity calculation is used with integer pixel pitch, then device complexity is reduced, but manufacturing precision deteriorates due to accumulated errors in the constructed fingerprint image
Solution Approach 1:
The patent transforms the movement quantity parameter from an integer value (based on pixel pitch) to a real number value through interpolation calculation. This parameter change enables precise representation of finger movement without the quantization errors inherent in integer-based systems, thereby improving fingerprint image construction accuracy while maintaining simple device architecture
Solution Approach 2:
The patent introduces interpolation calculation as an intermediary process between image acquisition and image construction. This intermediary step computes precise movement quantities by interpolating between adjacent pixels, serving as a bridge that eliminates direct pixel-pitch dependency and prevents error accumulation in the final fingerprint image
Data Source
AI summary
In construction processing of a fingerprint partial image, distortion occurs in the general image due to accumulation of coordinate errors at image joining positions. While a latest partial image read by a sweep type fingerprint sensor is being displaced relative to an already acquired partial image, a displacement quantity at each displacement position is found. By interpolation computation using the found values, a first vector component indicating a movement quantity of the latest partial image in the slide direction, and first and second candidates for a second vector component indicating a movement quantity in a direction perpendicular to the slide direction are calculated as values each having a resolution higher than the pixel pitch. The latest partial image is disposed so as to be joined to the already acquired partial image on the basis of a movement quantity vector including the first and second vector components.