Fringe Pattern Phase Offset Correction for 3D Topology
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Solution Overview
Problem
Fringe projection techniques face limitations in deriving accurate 3D surface information due to the need for exact synchronization between the projector and camera frame rates, which is not always feasible, leading to phase ambiguity and reduced accuracy in phase unwrapping and surface normal estimation.
Innovation Solution
The technique involves projecting shifted fringe patterns at a projector frame rate and capturing images at a camera frame rate, allowing for real-time derivation of topology information without exact synchronization by determining and correcting phase offsets using a processor, and utilizing additional depth sensors for phase unwrapping and surface normal estimation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If exact synchronization between projector and camera frame rates is implemented, then measurement precision of phase information is improved, but device complexity and ease of operation deteriorate due to complex synchronization requirements
Solution Approach 1:
A processor acts as an intermediary to analyze captured images and determine phase offset information between the projector and camera. Instead of requiring complex hardware synchronization, the processor computationally determines the phase relationship by analyzing the fringe patterns captured in images, thereby resolving the timing mismatch between the two devices.
Solution Approach 2:
The system changes the parameter being measured from absolute synchronized timing to relative phase offset. By determining the phase offset information from the captured images rather than relying on precise frame rate synchronization, the system transforms the problem from a timing-critical operation to a computational analysis task.
2Measurement precision
If exact synchronization between projector and camera frame rates is implemented, then measurement precision of surface normals is improved, but ease of operation deteriorates
Solution Approach 1:
The processor serves as an intermediary that computationally determines phase offset from captured images, eliminating the need for operators to manually synchronize frame rates. This automated computational approach maintains high measurement precision while significantly improving ease of operation.
3Device complexity
If phase offset determination and correction is implemented without exact synchronization, then device complexity is reduced, but measurement precision of phase information deteriorates
Solution Approach 1:
The system implements feedback by analyzing the captured images to determine phase offset information and then using this information to correct the phase measurements. The processor continuously monitors the fringe patterns and adjusts the phase calculations based on the determined offset, ensuring high measurement precision even without exact synchronization.
Solution Approach 2:
The system transforms the phase measurement problem by introducing phase offset as a correctable parameter. Instead of assuming perfect synchronization, the system explicitly determines and corrects for the phase offset, thereby maintaining measurement precision while reducing device complexity.
4Measurement precision
If additional depth sensors are used for phase unwrapping, then measurement precision of 3D data is improved, but device complexity increases
Solution Approach 1:
The camera serves multiple functions: it captures both the fringe pattern information needed for phase measurement and the depth information needed for phase unwrapping. By making the camera a multi-functional device, the system improves 3D measurement precision without adding separate depth sensing hardware, thereby avoiding increased device complexity.
Data Source
Figure 1
Figure 2A~2B
Figure 3
AI summary
An example apparatus has a processor to analyze images of projected shifted versions of a fringe pattern onto a scene to obtain phase information associated with the pixels in the image. Topology information is derived by correcting the phase information using a phase offset associated with a combination of two subsequent versions of the fringe pattern in the images or by estimating a surface normal for each pixel using a partial derivative of the phase information of the pixel in a first spatial direction and a partial derivative of the phase information of the pixel in a second spatial direction.