Digital Watermark Reader Pose Estimation via Structured Light
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Solution Overview
Problem
Current 2D indicia localization and decoding processes are limited by sensitivity to perspective distortion and irregularly shaped surfaces, which worsens decoding performance due to distortions caused by skewing and complex surface irregularities.
Innovation Solution
A digital watermark reader system that captures images with a light generation system projecting a cross-shaped aiming pattern or collimated light beam, allowing the processor to estimate distortions and decode watermarks based on the target object's pose and distance, using pre-computed distortion models and subsampling techniques to improve decoding accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional grid localization algorithms are used for 2D indicia decoding, then the decoding process is simple, but the system is highly sensitive to perspective distortion and surface irregularities, worsening decoding performance
Solution Approach 1:
The system performs preliminary pose estimation using a light projection system before decoding. The light generation system projects a known pattern onto the target object, and the imaging system captures the distorted pattern to estimate pose parameters (rotation, translation, scale) in advance. This preliminary action compensates for perspective distortion and surface irregularities before the actual decoding process, improving reliability without significantly increasing overall system complexity
Solution Approach 2:
The patent introduces an intermediary pose estimation step between image capture and decoding. The light projection system acts as a mediator that provides reference points for calculating distortion parameters. This intermediary process creates a transformation model that corrects the captured image, allowing traditional decoding algorithms to work effectively on corrected images while maintaining robustness against distortion
2Measurement precision
If the system captures images without light projection to maintain simplicity, then the device complexity is low, but the measurement precision of pose and distortion estimation deteriorates
Solution Approach 1:
The system changes the illumination parameter by projecting structured light patterns onto the target object. This light projection creates high-contrast reference features that significantly improve the precision of pose estimation. The known geometric pattern of projected light provides reliable reference points for calculating transformation parameters, enabling accurate measurement even with complex surfaces or perspectives
Solution Approach 2:
The patent uses optical vibration or modulation in the light projection system. The light generation system projects patterns that can be modulated or pulsed, creating temporal variations that help distinguish the projected pattern from background elements. This temporal modulation enhances the precision of detecting reference points and improving pose estimation accuracy
3Measurement precision
If the system uses active light projection and distortion estimation to improve decoding accuracy, then measurement precision improves, but the loss of time increases due to additional processing steps
Solution Approach 1:
The system uses periodic or pulsed light projection instead of continuous illumination. The light generation system projects patterns in brief pulses synchronized with the imaging system's capture timing. This periodic action reduces the total time required for data collection while providing sufficient information for accurate pose estimation, as the pulsed light creates distinct temporal markers that are easy to detect and process
Solution Approach 2:
The pose estimation using light projection is performed as a preliminary step that quickly establishes transformation parameters. Once these parameters are determined, the actual decoding process can proceed efficiently on corrected images. This preliminary action organizes the processing workflow to minimize total time, as the computationally intensive distortion correction is based on pre-calculated parameters from the light pattern analysis
Data Source
AI summary
Systems and methods of operation for a machine-readable symbol reader for estimating the relative position, orientation and/or distance of a scanned target object or item labeled with two dimensional (2D) indicia, such as a digital watermark. Such estimation information may be provided to a localization process or a decoding process to assist such processes in decoding the 2D indicia from an image of the object labeled with the 2D indicia. The machine-readable symbol reader may include an aiming system which projects a light pattern onto a target object. The reader may capture one or more images of the target object while the light pattern is projected thereon and analyze at least one characteristic of the pattern to estimate position, orientation or distance of the target object relative to the machine-readable symbol reader. Such information may be used to improve decoding of the 2D indicia.