ToF Range Imaging with Event-Gated Subframes Against Ambient Light
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Solution Overview
Problem
Existing ranging devices using the Time of Flight (ToF) method struggle with ambient light interference and inefficiencies in distance measurement accuracy, particularly when using Single Photon Avalanche Diode (SPAD) sensors for time-gating techniques.
Innovation Solution
A range image generation device employing a pixel array with avalanche photodiodes (APDs) and a signal processing circuit that utilizes global gate driving and event detection to differentiate between ambient and reflected light, generating range images based on signal changes across multiple frame periods.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If time-gating technique with SPAD sensor is used for ranging, then distance measurement capability is achieved, but ambient light interference deteriorates measurement precision
Solution Approach 1:
The patent divides the ranging frame into multiple sub-frames with different exposure timing relative to light emission. By segmenting the measurement process into multiple temporal segments (sub-frames), the system can distinguish reflected light signals at different time delays from ambient light, enabling accurate distance measurement despite ambient light interference.
Solution Approach 2:
The patent employs periodic light emission and periodic exposure gating synchronized with the light emission cycle. The SPAD sensor is gated to detect photons only during specific periods after light emission, creating a periodic detection pattern that allows discrimination between reflected light (returning after known time) and ambient light (random timing), thereby resolving the ambient light interference problem.
2Measurement precision
If multiple sub-frames are acquired for each pixel, then distance measurement accuracy is improved, but processing complexity and time consumption increase
Solution Approach 1:
The patent performs preliminary acquisition of multiple sub-frames for each pixel before final distance calculation. By pre-acquiring multiple sub-frames with different exposure timings, the system builds up sufficient signal statistics in advance, allowing more accurate distance measurement through statistical processing of the accumulated data without increasing real-time processing complexity.
Solution Approach 2:
The patent uses the event detector to monitor signal changes across sub-frames and provides feedback to the image generator. When signal changes are detected between sub-frames, the system identifies these as meaningful events and prioritizes their processing. This feedback mechanism allows the system to focus computational resources on pixels with significant changes rather than uniformly processing all pixels, reducing overall processing complexity while maintaining accuracy.
3Adaptability or versatility
If event detection is performed for signal changes across frame periods, then dynamic object detection capability is improved, but measurement time increases
Solution Approach 1:
The patent implements periodic event detection by comparing sub-frames at regular intervals. The event detector operates periodically, checking for signal changes between consecutive or间隔 sub-frames. This periodic operation allows dynamic objects to be detected through their temporal signal variations while maintaining efficient timing, as the detection rhythm is synchronized with the light emission cycle rather than requiring continuous monitoring.
Solution Approach 2:
The patent applies skipping by not continuously monitoring all pixels at all times, but rather sampling signal changes at specific intervals between sub-frames. The event detector skips intermediate time periods and only performs change detection at defined sampling points, reducing the total measurement time while still capturing dynamic object movements that occur between these sampling points.
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 distance measurement accuracy by reducing ambient light influence and improving range image generation efficiency through adaptive exposure periods and event detection, resulting in precise two-dimensional distance mapping.
Implementation Method 1
a plurality of pixels each including a photoelectric conversion element
Implementation Method 2
Single Photon Avalanche Diode (SPAD) sensor
Implementation Method 3
emitting light from a light source and detecting the light reflected by an object
Implementation Method 4
ranging by emitting light from a light source and detecting the light reflected by an object
Data Source
AI summary
A range image generation device is provided. The device includes an image generator to generate a range image based on outputs from pixels in each of ranging frame periods and an event detector. In each ranging frame period, sub-frames are acquired by detection operations in which time from a light emission timing until an exposure period is different. The event detector detects a change of a signal value in at least two ranging frame periods. In each ranging frame period, the image generator acquires a pixel value based on the sub-frames for a pixel for which the change is detected, and does not acquire a pixel value, or acquires the pixel value based on the sub-frames if a set condition is satisfied for a pixel for which no change is detected.