Time-of-Flight Sensor Phase Estimation via Ambient Light Rejection
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Solution Overview
Problem
Time of flight cameras experience errors in depth value estimation and confidence computation, particularly when used with strong background lights or stroboscopic sources, due to ambient light interference.
Innovation Solution
A device and method that utilize circuitry with an image sensor to obtain differential and common mode signals from pixels, estimating phase based on these signals and a background light rejection ratio to improve depth information accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional depth estimation methods are used in time of flight cameras, then depth information can be obtained, but the accuracy deteriorates under strong background lights and stroboscopic light sources
Solution Approach 1:
The pixel output signal is segmented into two distinct components: differential mode signal (representing depth information) and common mode signal (representing ambient light). This segmentation allows independent processing and estimation of each component, enabling the system to extract depth information while compensating for ambient light effects.
Solution Approach 2:
The common mode signal acts as an intermediary that captures ambient light information. By using this intermediary signal, the system can estimate and remove ambient light contributions from the differential mode signal, thereby improving depth estimation accuracy under varying lighting conditions.
2Measurement precision
If simple phase estimation from differential mode alone is used, then processing is simple, but accuracy deteriorates due to background light variations
Solution Approach 1:
The system employs a feedback mechanism where the common mode signal is continuously monitored and used to adjust the phase estimation process. The estimated ambient light level from the common mode signal feeds back into the differential mode processing to compensate for background light variations, improving accuracy without requiring complex hardware modifications.
Solution Approach 2:
The method changes the processing parameters by introducing a second input (common mode signal) that provides additional information about ambient light conditions. This parameter change enables dynamic adjustment of the phase estimation algorithm to account for varying lighting environments.
3Measurement precision
If additional signals and processing steps are added to improve accuracy, then depth estimation accuracy improves, but device complexity increases
Solution Approach 1:
The image sensor pixels are designed to provide multiple functions: they simultaneously generate both differential mode signals (for depth) and common mode signals (for ambient light measurement) using the same hardware infrastructure. This multi-functionality allows accurate depth estimation under varying lighting conditions without requiring separate dedicated sensors or complex additional circuitry.
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
The solution enhances the accuracy of depth information and reduces noise in time of flight sensors by effectively rejecting background light variations, leading to improved signal-to-noise ratio and robust performance under varying lighting conditions.
Implementation Method 1
an image sensor in the time of flight camera receives part of the reflected light. The time between the emission of light and the detection of its reflection on the image sensor may be measured
Data Source
AI summary
A device includes a circuitry which has an image sensor with a plurality of pixels, wherein the circuitry obtains a differential mode for a quad of each pixel from the plurality of pixels of the image sensor, being representative of a depth information; obtains a first input based on a common mode signal for the quad of the pixel, being representative of an intensity of ambient light; obtains a second input being representative of a background light rejection ratio of the pixel; and estimates a phase for the pixel from the plurality of pixels of the image sensor based on the differential mode, the first input and the second input.