CW-TOF Camera Structured Light Multipath Interference
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Continuous wave time of flight (CW-TOF) cameras face challenges in accurately determining distances to features due to multipath interference (MPI), which introduces errors in phase delay and distance measurements.
Innovation Solution
The CW-TOF camera employs structured light with different illumination zones and perturbation phase shifts to reduce MPI errors by making the contribution of multipath light photocharge independent of the sampling phase offset, using a structured illumination pattern and optical pattern modifiers synchronized with perturbation phase shifts to isolate and minimize MPI contributions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional CW-TOF camera uses uniform illumination to determine distances, then the device complexity is low, but measurement precision deteriorates due to multipath interference errors
Solution Approach 1:
The illumination is segmented into different illumination zones with distinct patterns. Each zone receives a specific structured light pattern (e.g., different phases or amplitudes) that enables the system to distinguish between direct light and multipath reflected light based on the spatial distribution of returned photons, thereby reducing MPI errors without requiring complex hardware modifications
Solution Approach 2:
Different regions of the scene are illuminated with locally optimized structured light patterns tailored to their specific geometric characteristics and expected MPI conditions. This allows the system to adapt the illumination quality locally to minimize multipath interference in critical measurement zones while maintaining simplicity in other areas
2Measurement precision
If CW-TOF camera applies structured light with perturbation phase shifts to reduce MPI errors, then measurement precision improves, but device complexity increases due to additional optical components and control mechanisms
Solution Approach 1:
The system employs periodic perturbation phase shifts applied to the structured light illumination. By modulating the light phase in a periodic sequence across different illumination zones, the system can distinguish direct path photons from multipath photons based on their different phase characteristics, improving phase delay measurement accuracy through temporal modulation rather than spatial complexity
Solution Approach 2:
The optical pattern modifiers dynamically adjust the structured light patterns in real-time according to the perturbation phase shift sequence. This dynamic control allows the system to encode spatial and temporal information that enables MPI rejection, achieving high measurement precision through adaptive optical control rather than static complex hardware
3Reliability
If CW-TOF camera uses multiple perturbation phase shifts for each sampling phase offset, then reliability of distance measurement improves, but productivity decreases due to increased exposure periods required
Solution Approach 1:
The system applies a limited sequence of perturbation phase shifts (e.g., 2-4 shifts) rather than exhaustive sampling. This partial action approach provides sufficient information to reliably distinguish direct from multipath light while minimizing the number of exposure periods required, thus maintaining imaging speed while achieving reliable measurements
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
This approach significantly enhances the camera's resistance to MPI errors, providing more accurate phase delay and distance measurements by isolating and minimizing the impact of multipath interference, resulting in improved range imaging accuracy.
Implementation Method 1
a light source operable to transmit structured light modulated at a modulation frequency to illuminate the scene
Implementation Method 2
a photosensor having a plurality of pixels configured to register amounts of light reflected from the transmitted light by features in the scene
Implementation Method 3
modulate sensitivity of the photosensor at the frequency of modulation of the transmitted light but phase shifted relative to phase of the transmitted light by a phase theta k,n
Data Source
Figure 1A
Figure 1B
Figure 2
AI summary
A method of determining distances to features in a scene comprising transmitting structured light modulated at a modulation frequency to illuminate the scene with a structured illumination pattern and for each combination of a sampling phase offset and a perturbation phase shift λη, modulating sensitivity of a photosensor at the frequency of modulation of the transmitted light, but phase shifted relative to phase of the transmitted light by a phase θk,n = (ψk + λη), and for each value of θk,η modulo 360°, registering light reflected by features in the scene during a different exposure and using the registered light to provide a range image of the scene.