Time-of-Flight Histogram Filtering for Reliable Object Detection
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Solution Overview
Problem
Existing time-of-flight sensors face challenges in accurately identifying bins representative of object presence due to photon dispersion, leading to false detections and reduced detection range, especially for low-reflective objects and autofocus applications.
Innovation Solution
A method involving transforming histogram bins into a transformed domain using a scatter graph to distinguish bins representative of object presence from those obscured by dispersion, utilizing a threshold function to identify and select bins based on their position relative to a defined limit.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a fixed threshold is used to identify bins representative of object presence, then the identification process is simple, but bins obscured by photon dispersion are misidentified leading to false detections
Solution Approach 1:
The patent transforms the one-dimensional histogram bins into a two-dimensional transformed domain using a scatter graph. Each bin is represented by coordinates (x, y) where x is the acquisition time and y is the number of detected photons. This dimensional transformation allows the use of a threshold function that varies with acquisition time, enabling reliable distinction between true object bins and dispersion bins while maintaining operational simplicity.
2Reliability
If the comparison threshold is raised to ignore bins with low photon counts, then false detections from dispersion are reduced, but detection of low-reflective objects and distant objects is compromised
Solution Approach 1:
The patent replaces the static fixed threshold with a dynamic threshold function that varies with acquisition time. The threshold function adapts to the expected photon dispersion pattern at different time points, allowing low thresholds at times when dispersion is minimal (enabling detection of low-reflective objects) and high thresholds at times when dispersion is expected (reducing false detections). This dynamic adaptation resolves the contradiction between reducing false detections and maintaining detection sensitivity.
3Productivity
If all bins following the main bin are considered representative of object presence, then detection coverage is maximized, but detection accuracy decreases due to inclusion of dispersion bins
Solution Approach 1:
The patent extracts and removes dispersion bins from the set of bins considered representative of object presence. By transforming bins into the two-dimensional domain and applying the time-varying threshold function, the method identifies and excludes bins that fall above the threshold (dispersion bins) while retaining bins below the threshold (true object bins). This extraction process maintains detection coverage for all true objects while eliminating false detections from dispersion.
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
Enhances the reliability of object detection by distinguishing true object bins from dispersed bins, improving detection accuracy and range, particularly for low-reflective objects and autofocus functions.
Implementation Method 1
a time-of-flight sensor is configured so as to be able to emit an optical light radiation, for example of the infrared or laser type, towards an object and to measure a flight time, that is to say the time elapsed between the emission of this radiation and its reception by the sensor after reflection of the radiation on the object
Implementation Method 2
The reception of the radiation may be performed using single-photon sensitive detectors. In particular, as single-photon sensitive detectors, there are known Single Photon Avalanche Diodes, commonly referred to by the acronym 'SPAD' by persons skilled in the art
Data Source
AI summary
A method can be used to detect the presence an object within a field of view of a time-of-flight sensor. A histogram generated by the time-of-flight sensor is obtained. The histogram includes a number of bins associating a number of detected photons to a given acquisition time. A portion of the bins of the histogram is transformed into points in a transformed domain that features a first area containing only points associated to bins representative of the presence of the object and a second area having only points associated to bins not representative of the presence of the object. The bins of the histogram representative of the presence of the object are identified from the points located in the first area.