Time-of-Flight Camera Dynamic Range via Multi-Exposure Phase Correlation
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Solution Overview
Problem
Time-of-flight cameras face challenges in generating high-quality depth maps due to limited dynamic range, leading to poor noise performance and oversaturation of pixels, especially when selecting exposure durations that compromise between bright and dim portions of a scene.
Innovation Solution
A method and system for a time-of-flight camera that determines phase-correlation values at each pixel for multiple exposure durations and phase offsets, accumulates valid correlations, and generates depth maps using these values, while also creating an amplitude image, employing weighting and normalization to improve dynamic range and noise performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If exposure duration is extended to improve noise performance, then signal quality improves, but pixel saturation occurs resulting in invalid depth data
Solution Approach 1:
The patent segments the exposure duration into multiple discrete time intervals or gates, allowing different portions of the reflected light signal to be captured separately. This segmentation enables the system to avoid saturation while maintaining signal quality by selectively integrating photons from specific time windows.
Solution Approach 2:
The patent implements dynamic adjustment of exposure duration based on scene conditions, allowing the system to adaptively optimize the exposure time for different brightness levels. This dynamic control enables the camera to prevent saturation in bright areas while maintaining adequate signal accumulation in darker regions.
2Reliability
If exposure duration is reduced to prevent pixel saturation, then depth data validity is maintained, but noise performance deteriorates
Solution Approach 1:
The patent merges multiple phase-correlation measurements taken at different exposure durations or time intervals to produce a final depth map. By combining these measurements, the system achieves both the reliability of short exposures (avoiding saturation) and the noise performance of long exposures (adequate signal accumulation).
Solution Approach 2:
The patent changes the exposure duration parameter across multiple measurements, capturing phase-correlation data at different exposure times. This parameter variation allows the system to select or combine measurements that are valid (not saturated) while maintaining adequate signal-to-noise ratio through the accumulation of multiple measurements.
3Device complexity
If a single exposure duration is used to simplify the imaging process, then device complexity is reduced, but dynamic range is limited
Solution Approach 1:
The patent employs periodic modulation of the light source and synchronized detection at multiple phase offsets during the exposure period. This periodic action enables the system to extract depth information for multiple distance ranges within a single exposure cycle, effectively expanding the dynamic range without requiring multiple separate imaging operations.
Solution Approach 2:
The patent makes the imaging system multi-functional by capturing both amplitude and phase-correlation information simultaneously at multiple exposure durations. This universal approach allows a single imaging operation to produce multiple depth maps with different exposure characteristics, providing adaptability across various scene conditions without increasing operational complexity.
Data Source
AI summary
A time-of-flight camera for generating a depth map indicating distance(s) to target(s) includes a processor and multi-pixel time-of-flight image sensor. The camera: (a) determines, at each pixel, a plurality of phase-correlation values associated with at least one exposure duration and at least one phase offset; (b) determines for each pixel an accumulated correlation in response to the plurality of phase-correlation values; and (c) generates the depth map in response to a plurality of the accumulated correlations. A set of accumulated correlations may be determined in response to a plurality of sets of phase-correlation values such that each accumulated correlation is associated with one unique phase offset in response to each set of phase-correlation values being associated with one exposure duration, the depth map being generated in response to a plurality of sets of accumulated correlations. A computer-implemented method of generating a depth map using a time-of-flight image sensor is provided.