Weighted Filtering for SPAD Dark Current Compensation
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Solution Overview
Problem
Conventional image sensors, particularly CMOS and CCD sensors, suffer from high read noise and motion blur under low light conditions, affecting image quality and other operations in mixed-reality systems, while SPAD sensors face challenges with dark current noise that degrades image quality and consistency.
Innovation Solution
Implement systems and methods for generating dark current residual images to compensate for dark current noise in SPAD imagery, using template matching, non-maximum suppression, and weighted filtering to refine dark current images, and combine them with motion-compensated previous images based on ambient light conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If SPAD sensors are used to improve signal detection in low light conditions, then sensitivity to photons is improved, but dark current noise increases and degrades image quality
Solution Approach 1:
The patent extracts and removes dark current noise from SPAD sensor data by generating a dark current image separately and subtracting it from the original captured image. This extraction process isolates the harmful dark current component while preserving the useful signal information, thereby improving image quality while maintaining the sensor's high sensitivity.
Solution Approach 2:
The patent converts the harmful dark current noise into a useful tool for improving image quality. By capturing a separate dark current image and using it to create a corrected image through subtraction, the system transforms the previously detrimental dark current into a compensatory element that enhances the overall image quality and reduces noise artifacts.
2Reliability
If conventional CMOS/CCD sensors are used, then device maturity is improved, but read noise and motion blur increase under low light conditions
Solution Approach 1:
The patent replaces the conventional CMOS/CCD imaging system with a SPAD-based system that uses single-photon avalanche detection. This substitution eliminates the read noise and motion blur problems inherent in conventional sensors by using a different detection mechanism that counts individual photons without requiring readout operations that introduce noise.
3Measurement precision
If dark current images are generated and subtracted, then dark current compensation is improved, but image processing complexity increases
Solution Approach 1:
The patent performs preliminary action by capturing a separate dark current image under controlled conditions before processing the main captured image. This pre-captured dark current image serves as a reference that simplifies the subsequent subtraction process, as the dark current characteristics are already characterized and stored, reducing the complexity of real-time 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
Improves image quality and consistency in low light conditions by accurately compensating for dark current noise, reducing false counts and noise in SPAD imagery, and enhancing user experiences in mixed-reality environments.
Implementation Method 1
Some MR systems include one or more cameras for facilitating image capture, video capture, and/or other functions. For instance, cameras of an MR system may utilize images and/or depth information obtained using the camera(s)
Implementation Method 2
image sensing pixel arrays where each pixel is configured to generate electron-hole pairs in response to detected photons
Data Source
AI summary
A system for facilitating dark current compensation by weighted filtering is configurable to (i) receive an input dark current image; (ii) generate a corrected dark current image at least by scaling pixel values of the input dark current image based upon ambient light conditions; and generate a weight map comprising a weight value for each pixel of the corrected dark current image. For each pixel of the corrected dark current image, the weight value of the weight map may be based upon a light level of the pixel of the corrected dark current image. The system is also configurable to generate an output image by utilizing the weight map to filter an input image.