dToF Anti-Flicker Filtering With Confidence-Weighted Target Tracking
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Solution Overview
Problem
ToF devices suffer from flicker effects due to temporal fluctuations in target detection, which existing methods like hysteresis filters and spatial correlation fail to adequately address, particularly in single-zone sensors, introducing latency and reducing spatial resolution.
Innovation Solution
A confidence-based flicker filtering method and system that uses temporal filtering with short and long-term memory, employing weighted filters like IIR and FIR to reduce flicker while maintaining low latency and spatial resolution, handling multiple targets and false detections.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If statistical detection is used to identify targets in ToF sensor, then target detection capability is enabled, but flicker occurs where targets are detected at one instant then lost at the next
Solution Approach 1:
The system performs preliminary actions by maintaining a history of previously detected targets and their parameters. Before making a detection decision at the current instant, the system checks against historical data to anticipate and prevent flicker, ensuring stable target identification without introducing harmful latency.
Solution Approach 2:
The system implements feedback by continuously comparing current detection results with historical detection data. The histogram pipe firmware uses feedback from previous frames to adjust threshold decisions and maintain consistent target detection, reducing flicker while keeping latency minimal through efficient feedback loops.
2Stability of the object's composition
If hysteresis filter is used to reduce flicker, then temporal stability is improved, but latency is introduced
Solution Approach 1:
The system applies partial hysteresis filtering only when necessary - specifically when detection confidence is near the threshold. Instead of applying strong filtering always (which would cause excessive latency), the system uses subtle threshold adjustments based on historical confidence levels, achieving stability with minimal latency penalty.
Solution Approach 2:
The hysteresis threshold is made dynamic rather than fixed. The threshold adapts based on the detected target's history and confidence levels, allowing the system to be more aggressive when confident and more conservative when uncertain, thereby reducing overall latency while maintaining stability.
3Reliability
If spatial correlation is exploited to reduce flicker, then detection stability improves, but spatial resolution is reduced
Solution Approach 1:
The system segments the spatial processing from temporal processing. Spatial resolution is maintained by keeping the pixel-level detection independent, while temporal stability is achieved by applying the anti-flicker filter at the target-level in firmware. This segmentation allows full spatial resolution to be preserved while still exploiting temporal correlations for flicker reduction.
Solution Approach 2:
The histogram pipe firmware acts as an intermediary layer between the sensor hardware and the application. It receives high-resolution spatial data from the sensor, applies temporal filtering to reduce flicker, and outputs stable target information without degrading the original spatial resolution. The intermediary preserves spatial fidelity while adding temporal stability.
4Device complexity
If single-zone sensor is used, then device complexity is reduced, but spatial correlation cannot be exploited for flicker reduction
Solution Approach 1:
The system makes the single-zone sensor self-sufficient by implementing the anti-flicker functionality within the histogram pipe firmware itself. Instead of relying on spatial correlation from multiple zones (which would increase complexity), the firmware uses temporal history and confidence tracking to provide flicker reduction, allowing the simple single-zone sensor to achieve reliable detection.
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
Drastically reduces flicker by up to 90% at the output of the Histogram Pipe, maintains reasonable latency, and smoothly handles multiple targets without reducing spatial resolution, offering a tunable trade-off between stability and latency.
Implementation Method 1
A photon may generate a carrier in the SPAD through the photoelectric effect
Implementation Method 2
The photo-generated carrier may trigger an avalanche current in one or more of the SPADs in the SPAD array
Implementation Method 3
Time-of-Flight (ToF) devices directly measure the time taken by the signal to travel to the object and travel back to the device
Implementation Method 4
Indirect Time of Flight (iToF) devices calculate the time the signal takes to travel by measuring the phase shift between the signal coming out of the light source and the signal reflected from the object
Data Source
AI summary
Method, having detecting from a first histogram signal delivered by a sensor device, successive sets of targets at respective successive instants, determining for a current set of current detected targets, a current histogram output, the current histogram output having for each current detected target of the current set, a current group of parameters stored in a memory including a confidence indicator, performing a matching operation between the current set of detected targets and previous sets of detected targets stored in the memory, and performing a filtering operation of at least one parameter of the current group of parameters of at least some of the current detected targets of the current set, on the basis of the result of the matching operation, the filtering operation being weighted on the basis of at least the confidence indicators of current and previous sets of detected targets.