ToF Pixel Array Homogenization for SPAD Detection Holes
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Solution Overview
Problem
High-resolution Time of Flight (ToF) sensors face sensitivity non-uniformity and defects in single-photon avalanche diodes (SPADs), leading to false detection holes and inconsistent sensitivity across the pixel array, which current interpolation methods fail to accurately address.
Innovation Solution
A method and system for homogenizing pixel values by analyzing neighboring targets, computing an equivalent target detection confidence indicator, and deciding whether to fill holes based on sensitivity and pattern analysis, using parameters like ambient noise, SPAD count, and integration time.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If classical interpolation methods are used to fill detection holes, then the processing is simple and fast, but the accuracy is poor because real target holes cannot be distinguished from false detection holes
Solution Approach 1:
The patent applies preliminary action by pre-calculating and storing sensitivity correction factors for each pixel based on their individual sensitivity characteristics. This pre-processing step allows the system to quickly compensate for sensitivity variations during target detection without adding complex real-time processing, thereby improving detection accuracy while maintaining processing efficiency.
Solution Approach 2:
The patent changes the detection parameter by introducing an equivalent target detection confidence indicator that incorporates pixel sensitivity information. Instead of using raw detection values, the system transforms the detection parameter to include sensitivity compensation, which enables accurate distinction between real target holes and false detection holes while maintaining computational feasibility.
2Measurement precision
If sensitivity compensation is applied to correct pixel non-uniformity, then detection accuracy improves, but processing time increases due to additional calculations
Solution Approach 1:
The patent performs sensitivity compensation calculations in advance during system initialization or calibration phase, storing the results as lookup tables or correction factors. During actual target detection, the system simply applies these pre-computed corrections rather than performing complex calculations in real-time, thus achieving uniform detection accuracy across all pixels without significant processing time penalty.
Solution Approach 2:
The patent creates an equivalent virtual pixel response by computing what the detection confidence indicator would be if a target were present at the hole pixel location. This copied or simulated response allows the system to evaluate potential targets without requiring actual photon detection at every pixel location, reducing processing time while maintaining detection uniformity.
3Measurement precision
If the detection threshold is lowered to detect faint targets, then detection sensitivity increases, but false detection holes increase due to noise
Solution Approach 1:
The patent transforms the detection parameter by computing an equivalent target detection confidence indicator that incorporates pixel sensitivity information. This parameter transformation allows the system to maintain high detection sensitivity while filtering out false detections, because the confidence indicator accounts for each pixel's noise characteristics and sensitivity variations, enabling reliable distinction between true targets and noise-induced false holes.
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
Accurately determines the presence of targets in holes, mitigating sensitivity variations, correcting dead pixels, and increasing maximum range without latency, all within the sensor's embedded firmware processing.
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 a SPAD pixel array
Implementation Method 3
This method comprises sending a light signal towards the object and measuring the time taken by the signal to travel to the object and to travel back to the device
Implementation Method 4
iToF (indirect Time of Flight) devices calculate the time taken by the signal for this travel by measuring the phase shift between the signal coming out of the light source and the signal reflected from the object
Data Source
Figure 1~2
Figure 3
Figure 4
AI summary
The method (200) for homogenizing values of a pixel array, comprises: - identifying (210, 212) pixels where a target has been detected, and correctable hole pixels (px_k) where no target has been detected, surrounded with at least one neighboring pixel where a target has been detected, - computing (220) an equivalent target detection confidence indicator for each correctable hole pixel (px_k), according to target feature values calculated for the neighboring pixels (px_i) of the correctable hole pixel, the equivalent target detection confidence indicator being representative of the target detection confidence indicator that the target detected in the neighborhood would have at the correctable hole pixel if the target detected in the neighborhood was also present at the correctable hole pixel position, in accordance with parameters including a sensitivity of the hole pixel, - if the computed equivalent target detection confidence indicator is lower than a detection threshold, computing (222) a correction target feature value, associated to the hole pixel.