CW ToF Depth Filtering with Coded-Modulation Masks
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Solution Overview
Problem
Conventional continuous-wave (CW) TOF measurements suffer from phase ambiguity due to periodic correlation waveforms, leading to unwanted background responses from highly reflective objects, and additional measurements are required to resolve this ambiguity, increasing data storage and processing demands.
Innovation Solution
A method combining continuous-wave phase measurements with coded-modulation measurements to generate a mask, where the coded-modulation measurement is used to determine a mask value applied to the CW phase measurements, effectively filtering out ambiguous distance values and reducing the need for additional exposures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional CW TOF measurements are performed with periodic correlation waveforms, then depth measurements can be obtained, but phase ambiguity occurs leading to erroneous background responses from highly reflective objects
Solution Approach 1:
The patent segments the measurement process into two distinct parts: (1) performing conventional CW TOF phase measurements to obtain initial depth values, and (2) performing separate coded-modulation measurements to generate a mask that identifies valid measurements. This segmentation allows the system to maintain the simplicity of CW measurements while adding a validation layer to eliminate ambiguous responses.
Solution Approach 2:
The patent introduces a mask generated from coded-modulation measurements as an intermediary element that mediates between the CW phase measurements and the final depth map. The mask acts as a filter that selectively validates or invalidates depth measurements based on coded-modulation correlation values, thereby eliminating erroneous background responses without modifying the original CW measurement process.
2Reliability
If additional phase set measurements are performed with different reference signal frequencies to resolve ambiguity, then measurement reliability improves, but data storage and processing requirements increase
Solution Approach 1:
The patent extracts the ambiguity resolution function from the main measurement process by using coded-modulation measurements specifically for generating a validation mask. Instead of performing multiple complete phase measurement sets with different frequencies, the system extracts only the necessary validation information through coded-modulation correlation measurements, thereby reducing data storage and processing requirements.
Solution Approach 2:
The patent changes the measurement parameter from multiple frequency sets to a single frequency with coded-modulation validation. By using coded-modulation sequences with distinct autocorrelation properties, the system achieves ambiguity resolution through parameter changes in the correlation function rather than through multiple frequency measurements, reducing computational complexity.
3Measurement precision
If multiple sequential exposures are performed for CW TOF measurements, then depth map accuracy improves, but measurement time increases
Solution Approach 1:
The patent merges two measurement approaches by performing coded-modulation measurements alongside the conventional CW phase measurements. By combining these measurements in a unified process and using the coded-modulation results to validate the phase measurements, the system achieves accurate depth maps without requiring additional sequential exposures, thereby reducing measurement time.
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 combined approach provides unambiguous depth measurements without increasing measurement count, reducing data storage and processing requirements, while maintaining depth resolution and eliminating erroneous background responses.
Implementation Method 1
depth measurements, i.e., measurements of the distance to various features of an object or objects in view of an image sensor may be performed as so-called time-of-flight (ToF) measurements, which are distance measurements determined using the speed of light
Implementation Method 2
performing a coded-modulation measurement for the first pixel... using a reference signal having a cross-correlation function, relative to a waveform that modulates emitted light illuminating an object of interest
Data Source
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AI summary
An example method for performing depth measurements with an image sensor comprises, for at least a first pixel, performing one or more continuous-wave phase measurements for the first pixel and performing a coded-modulation measurement for the first pixel. The method further comprises determining a mask value for the first pixel, based on the coded-modulation measurement, and applying the mask value to a distance value calculated from the one or more continuous-wave phase measurements, to obtain a masked distance value for the first pixel that has no ambiguity due to phase wrapping.