Time-of-Flight Image Pixel Background Light Separation
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Solution Overview
Problem
Conventional imaging devices face challenges in capturing depth information effectively, particularly due to difficulties in separating background intensity from reflected light pulse intensity, which can lead to inaccurate distance measurements and confusion from intrinsic brightness variations in real-world scenes.
Innovation Solution
The implementation of time-of-flight image pixels with charge storage regions and transfer transistors that differentiate between background light and reflected light, allowing for the measurement of time-of-flight differences and the extraction of depth information by processing circuitry to form accurate depth images.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If range finders determine depth information based on the brightness of reflected light, then depth information can be captured, but the system may be confused by differences in intrinsic brightness of objects
Solution Approach 1:
The patent segments the light collection process into distinct time intervals: a first time interval for collecting background light, and a second time interval for collecting reflected light pulses. This temporal segmentation allows the system to separately measure and subtract background intensity from the reflected light signal, eliminating confusion from intrinsic brightness variations of objects.
Solution Approach 2:
The system performs preliminary measurement of background light intensity before measuring the reflected light pulse intensity. By collecting background light in a first time interval and storing this information, the system can subsequently subtract this background component from the total light signal, isolating the reflected pulse component for accurate depth calculation.
2Measurement precision
If light sensors collect light for a predetermined time after emission, then closer objects can be detected, but far away objects may not return light during the collection period
Solution Approach 1:
The patent implements dynamic adjustment of the light collection time interval based on the detected time-of-flight characteristics. The system initially uses a first collection interval optimized for nearby objects, then extends to a second, longer collection interval for distant objects. This dynamic adaptation allows the same sensor system to effectively detect objects at varying distances without hardware changes.
Solution Approach 2:
The system employs periodic light emission and corresponding periodic collection intervals. By emitting light pulses at regular intervals and using multiple collection periods with different durations, the system can accommodate the varying return times of reflected light from objects at different distances, ensuring both near and far objects are captured.
3Measurement precision
If arrays of image sensors are used to capture depth information using parallax effect, then depth can be determined, but the system is limited to relatively short distances
Solution Approach 1:
The patent replaces the mechanical parallax-based depth measurement system with an optical time-of-flight measurement system. Instead of using multiple image sensors at fixed positions to triangulate depth, the system uses a single or array of light sensors that measure the time for light to travel to and from objects. This substitution of measurement mechanism enables accurate depth measurement at much longer distances beyond the effective range of parallax methods.
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 solution enables improved capture of depth images by effectively removing background light contamination and accurately determining object distances, even in complex scenes with varying brightness, thereby enhancing the precision and reliability of depth information.
Implementation Method 1
A time-of-flight image pixel may include a photosensitive element such as a photodiode
Data Source
AI summary
Electronic devices may include time-of-flight image pixels. A time-of-flight image pixel may include first and second charge storage regions coupled to a photosensor and a transfer transistor with a gate terminal coupled to the first storage region. An electronic device may further include a light pulse emitter configured to emit pulses of light to be reflected by objects in a scene. Reflected portions of the emitted pulses of light may be captured along with background light by the time-of-flight image pixels. Time-of-flight image pixels may be configured sense the time-of-flight of the reflected portions of the emitted pulses. The electronic device may include processing circuitry configured to use the sensed time-of-flight of the reflected portions to generate depth images of a scene. Depth images may include depth-image pixel values that contain information corresponding to the distance of the objects in the scene from the electronic device.