Time-of-flight depth camera indirect reflection suppression
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Solution Overview
Problem
Time-of-flight depth imaging is prone to systematic measurement errors due to indirect reflection of probe light, which falsely increases the measured depth of subjects, especially those with diffuse reflective surfaces, leading to a reduced signal-to-noise ratio.
Innovation Solution
Irradiating the subject with pulsed light of spatially alternating bright and dark features, where the depth sensing method maps the subject based on signals from pixels directly irradiated by bright features while omitting or weighting negatively signals from pixels under dark features, thereby reducing the impact of indirect reflections and enhancing the signal-to-noise ratio.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If uniform pulsed light is used to illuminate the subject, then all pixels receive sufficient signal for depth measurement, but indirect reflections from brightly illuminated areas contaminate the signal and reduce measurement precision
Solution Approach 1:
The illumination pattern is segmented into alternating bright and dark features (e.g., stripes or bars) across the subject. This segmentation allows the system to spatially separate direct reflections (from bright features) from indirect reflections (from dark features), enabling the photodetector to distinguish and preferentially process signals from direct reflections, thereby improving depth measurement precision while reducing contamination from indirect reflections
Solution Approach 2:
Different regions of the subject receive different illumination qualities - some regions (bright features) receive high-intensity pulsed light while adjacent regions (dark features) receive low or zero intensity. This local quality differentiation creates distinct signal characteristics that allow the system to identify and weight signals from direct reflections more heavily, improving measurement precision without suffering from indirect reflection contamination
2Measurement precision
If probe light power is concentrated on specific features, then signal intensity from direct reflections increases, but the area covered by effective illumination decreases
Solution Approach 1:
The system employs periodic pulsed illumination with spatially alternating bright and dark features. The pulsed nature allows time-gated detection to isolate direct reflections, while the spatial alternation ensures that within each pulse cycle, both bright and dark regions are present. This periodic action maintains high signal-to-noise ratio through concentrated power on bright features while the repeating pattern ensures comprehensive area coverage over time
Solution Approach 2:
The illumination pattern adds a spatial dimension (alternating bright/dark features across the field of view) to the temporal dimension (pulsed illumination). This dimensional expansion allows the system to concentrate power on specific spatial regions (bright features) during each pulse while maintaining overall area coverage through the extended illumination pattern, thereby improving signal-to-noise ratio without sacrificing illuminated area
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 effectively increases the signal-to-noise ratio for depth sensing by concentrating the probe light's power on bright features, reducing indirect reflections, and providing a more accurate depth measurement by doubling the signal intensity from direct reflections while eliminating signal from indirect reflections.
Implementation Method 1
In time-of-flight (TOF) depth imaging, a subject is irradiated by pulsed or otherwise modulated probe light. Some of the probe light reflects back from the subject to an imaging photodetector... the pixel-resolved time of flight of the probe light from its origin at the probe emitter, out to the subject, and back to the photodetector
Implementation Method 2
Some of the probe light reflects back from the subject to an imaging photodetector... indirect reflection of the probe light from one subject locus to another, and then to the photodetector
Data Source
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AI summary
A depth-sensing method for a time-of-flight depth camera includes irradiating a subject with pulsed light of spatially alternating bright and dark features, and receiving the pulsed light reflected back from the subject onto an array of pixels. At each pixel of the array, a signal is presented that depends on distance from the depth camera to the subject locus imaged onto that pixel. In this method, the subject is mapped based on the signal from pixels that image subject loci directly irradiated by the bright features, while omitting or weighting negatively the signal from pixels that image subject loci under the dark features.