TOF Camera Signal De-aliasing via Dual-Frequency Correlation
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Solution Overview
Problem
Conventional Time-of-Flight (TOF) camera systems face challenges with aliasing, which leads to measurement ambiguity due to the periodic nature of the illumination source, limiting the unambiguous distance range and requiring complex techniques that are computationally intensive and prone to bandwidth overheads.
Innovation Solution
The method involves using two correlation processes, one for determining distance and another for identifying aliasing, with the first process prioritized and potentially longer integration time, and employing multiple frequencies to reduce aliasing ambiguity, along with confidence thresholds based on distance-dependent factors like reflectivity and speckle size.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a single high-frequency correlation process is used for distance determination, then depth accuracy is improved, but aliasing occurs leading to measurement ambiguity
Solution Approach 1:
The patent divides the single correlation process into two separate correlation processes operating at different frequencies. The first correlation process operates at a higher frequency for accurate distance measurement, while the second correlation process operates at a lower frequency to detect aliasing. This segmentation allows the system to maintain high measurement precision while simultaneously detecting and correcting for aliasing errors, thus resolving the contradiction between depth accuracy and measurement reliability.
2Length of stationary object
If multiple frequencies are used for de-aliasing, then unambiguous distance range is increased, but computational overhead increases
Solution Approach 1:
The patent extracts the aliasing detection function from the main distance measurement process by implementing a separate, dedicated second correlation process. This extracted function specifically identifies aliasing conditions without interfering with the primary high-frequency distance measurement. By separating these functions, the system extends the unambiguous distance range while minimizing computational overhead, as each process is optimized for its specific purpose rather than attempting to do both simultaneously.
3Measurement precision
If longer integration time is used for aliasing detection, then aliasing identification accuracy is improved, but processing time increases
Solution Approach 1:
The patent implements dynamic prioritization where the first correlation process (distance measurement) is given higher priority and longer integration time, while the second correlation process (aliasing detection) operates with shorter integration time. The system dynamically adjusts the allocation of processing resources based on the functional requirements of each process, ensuring that the primary measurement function receives sufficient integration time for accuracy while the secondary detection function operates efficiently with reduced time overhead.
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 allows for efficient de-aliasing of TOF signals, increasing the unambiguous distance range, reducing reflectivity limitations, and improving depth accuracy while minimizing computational overhead and noise impact.
Implementation Method 1
each pixel effectively comprises a photosensitive element which receives incident light and converts it into an electrical signal
Implementation Method 2
The time-of-flight can be calculated in a separate processing unit which is coupled to the sensor or may be integrated into the sensor
Data Source
AI summary
Described herein is a method and sensor of processing time-of-flight (TOF) signals in a TOF camera system including an illumination unit and an imaging sensor. The method comprises illuminating the scene with light at a first frequency, detecting reflected light from at least one object in the scene at the first frequency, and determining a phase measurement using I and Q values. In addition, the scene is illuminated with light at a second frequency, the second frequency being 2−n of the first frequency where n=1, 2, . . . , etc., and the signs of I and Q values for both the first and second frequencies is used to determine the presence of aliasing in the phase measurement so that it can be corrected. The phase measurement is then corrected for aliasing and the effective range of the TOF camera system is extended by multiples of 2n. In addition, relative signal strength needs to be considered in accordance with the reflectivity of objects within the scene. For a reflectivity of 4% and no aliasing, the ability to detect an object decreases with distance (30). For an aliased phase measurement for an object with a reflectivity of 100%, the ability to detect the object is substantially constant (35).