Partial Reset Pixel Rows for CW-ToF Depth Accuracy
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Solution Overview
Problem
Continuous Wave (CW) Time-of-Flight (ToF) camera systems face inaccuracies and blurring due to the time required for emitting laser light and reading charge from the image sensor, especially when imaging moving objects, leading to reduced image quality and increased energy consumption.
Innovation Solution
The implementation of a partial reset technique for a subset of rows in the imaging sensor, allowing charge to accumulate additively on non-reset rows, enabling faster readout times and reduced integration time without compromising accuracy, by approximating the charge from adjacent rows with different integration settings.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the imaging sensor reads out charge from all rows after complete integration, then measurement precision is maintained, but readout time increases causing motion blur and inaccuracies
Solution Approach 1:
The pixel array is divided into multiple rows with different integration timing. Some rows (first row) complete integration and are reset, while other rows (second row) continue accumulating charge. This segmentation allows staggered readout of different row groups, reducing overall readout time while maintaining measurement precision for each row through its optimal integration period.
Solution Approach 2:
The imaging sensor performs periodic integration and readout cycles on different row groups. During each cycle, odd rows may be readout while even rows continue integrating, then vice versa. This periodic staggering reduces the total time the sensor is in readout mode, minimizing motion blur while preserving depth measurement accuracy through multiple sampling opportunities.
2Measurement precision
If integration time is extended to improve depth measurement accuracy, then measurement precision improves, but the system becomes slower and more prone to motion blur
Solution Approach 1:
Different rows are assigned different integration durations based on their position and imaging requirements. This segmentation allows the system to achieve high measurement precision for rows needing longer integration while maintaining high imaging speed for rows that can use shorter integration, effectively resolving the speed-precision tradeoff across the entire image.
Solution Approach 2:
The integration time parameter is varied across different rows of the pixel array. By changing the integration duration parameter for different row groups, the system optimizes depth measurement accuracy for each region while controlling overall imaging speed, allowing flexible adaptation to different scene requirements.
3Measurement precision
If multiple modulation frequencies are used to resolve phase wrapping, then measurement precision improves, but the time required to acquire and process data increases
Solution Approach 1:
The sensor alternates between different modulation frequency measurements in a periodic manner, acquiring data from multiple rows simultaneously at each frequency stage. This periodic multi-frequency approach resolves phase wrapping for accurate depth measurement while reducing total acquisition time through parallel row processing.
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 reduces inaccuracies and blurring in generated image information, enhances imaging speed, and optimizes energy efficiency, particularly beneficial for capturing moving objects and scenes with high dynamic range.
Implementation Method 1
an imaging sensor, the image sensor comprising a pixel array for accumulating charge based on incident light comprising reflected laser light off an object
Data Source
AI summary
There is provided a continuous wave time of flight, CW-ToF, camera system comprising: a laser for emitting laser light; an imaging sensor, the image sensor comprising a pixel array for accumulating charge based on incident light comprising reflected laser light off an object, the pixel array comprising a plurality of rows of pixels; and a control system coupled to the imaging sensor and configured to control the pixel array to: reset at least a first row and a second row of the plurality of rows, wherein the first row and the second row are adjacent one another in the pixel array; accumulate charge in the pixels of the pixel array using a first integration setting for a first time period; reset the first row of the plurality of rows; accumulate charge in the pixels of the pixel array using the first integration setting or a second integration setting for a second time period subsequent to the first time period; read out a set of charge samples, wherein the first row contains a first charge from accumulating after the second time period and the second row contains a second charge from accumulating after the first and second time periods; and use the set of charge samples to approximate a charge from sampling after the first time period.