Depth Mapping MPI Mitigation Using Reference Illumination Pattern
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Solution Overview
Problem
Indirect Time of Flight (iTOF) depth mapping systems face inaccuracies due to multi-path interference (MPI) caused by stray reflections, leading to errors in computing depth coordinates, particularly in wide-angle illumination setups.
Innovation Solution
The system employs a dual illumination approach, using both wide-field and narrow-field modulated optical radiation, where the wide-field radiation is corrected using the more precise but noise-prone narrow-field depth coordinates to mitigate MPI effects, enabling accurate depth mapping by processing circuitry.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If wide-field optical radiation is used for depth mapping, then the coverage area and field of view are improved, but multi-path interference increases causing measurement precision to deteriorate
Solution Approach 1:
The illumination is segmented into multiple angular components using separate VCSEL emitter groups (first group for wide angles, second group for narrow angles). This segmentation allows the system to capture both wide coverage and high precision measurements by processing signals from different angular ranges separately and combining them appropriately.
Solution Approach 2:
Different regions of the illumination field are assigned different qualities - the center region uses narrow-angle illumination for high precision measurements, while the peripheral regions use wide-angle illumination for broad coverage. This local quality differentiation resolves the contradiction by optimizing each region for its specific requirements.
2Measurement precision
If narrow-field optical radiation is used for depth mapping, then measurement precision is improved, but the coverage area and field of view are reduced
Solution Approach 1:
The system merges the measurement data from both wide-field and narrow-field illumination by combining signals from multiple VCSEL emitter groups. The processing circuitry integrates the high-precision narrow-angle measurements with the broad-coverage wide-angle measurements to produce a complete depth map that achieves both precision and coverage.
Solution Approach 2:
The solution adds the angular dimension as a separate measurement variable. By measuring depth at multiple angular ranges (wide angles and narrow angles) and combining these dimensional measurements, the system achieves both wide coverage and high precision without sacrificing either requirement.
3Measurement precision
If multiple VCSEL emitter groups are used to mitigate MPI, then measurement precision is improved, but device complexity increases
Solution Approach 1:
Multiple VCSEL emitter groups serve multiple functions - they provide both wide-field illumination for coverage and narrow-field illumination for precision measurements. The same hardware infrastructure (VCSEL array, photodetector array, processing circuitry) handles both measurement modes, making the system multi-functional and reducing overall complexity despite the added capability.
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 method enhances the precision and accuracy of depth measurements by correcting for MPI-induced errors, resulting in improved depth maps with reduced artifacts and increased reliability in iTOF-based systems.
Implementation Method 1
Indirect Time of Flight (iTOF) depth mapping systems face inaccuracies due to multi-path interference (MPI) caused by stray reflections
Implementation Method 2
A receiver, such as a sensitive, high-speed photodiode (for example, an avalanche photodiode) or an array of such photodiodes, receives the light returned from the scene
Data Source
AI summary
Apparatus for optical sensing includes an illumination assembly, which directs first optical radiation toward a target scene over a first range of angles and second optical radiation over at least one second range of angles, which is smaller than and contained within the first range, while modulating the optical radiation with a carrier wave having at least one predetermined carrier frequency. A detection assembly includes an array of sensing elements, which output respective signals in response to the first and the second optical radiation. Processing circuitry drives the illumination assembly to direct the first and the second optical radiation toward the target scene in alternation, and processes the signals output by the sensing elements in response to the first optical radiation in order to compute depth coordinates of points in the target scene, while correcting the computed depth coordinates in response to the second optical radiation.