Image Sensor Dark Current Correction via Pixel Cluster Segmentation
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Solution Overview
Problem
Image sensors face inaccuracies in representing external scenes due to non-uniform dark current, particularly in low-light conditions and high temperatures, leading to suboptimal image reproduction.
Innovation Solution
An imaging system with a dark pixel array generates black reference signals to determine a global black level value, which is adjusted on a per-pixel or per-pixel cluster basis using a local gain correction factor, compensating for non-uniform dark current through comprehensive black level correction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If dark current correction is applied using a single global black level value, then processing complexity is reduced, but image accuracy deteriorates due to non-uniform dark current across the sensor
Solution Approach 1:
The pixel array is divided into multiple pixel clusters, with each cluster having its own local black level value. This segmentation allows the system to account for spatial non-uniformity in dark current while maintaining manageable processing complexity through localized rather than fully individual pixel correction.
Solution Approach 2:
Instead of applying a uniform global black level correction across the entire sensor, the patent implements local black level values for different pixel clusters. This local quality approach matches the physical reality of non-uniform dark current distribution, improving image accuracy by adapting the correction to local conditions.
2Measurement precision
If per-pixel black level correction is implemented, then image accuracy is improved, but device complexity increases due to additional processing requirements
Solution Approach 1:
The patent segments the pixel array into pixel clusters, applying black level correction at the cluster level rather than individual pixel level. This reduces the number of parameters that need to be stored and processed compared to full per-pixel correction, while still capturing the spatial non-uniformity of dark current.
Solution Approach 2:
The patent applies partial correction by using pixel clusters as the unit of correction rather than individual pixels. This partial action approach provides sufficient correction for most practical purposes while avoiding the excessive processing complexity of complete per-pixel correction.
3Ease of operation
If dark current is not corrected, then processing simplicity is maintained, but image fidelity deteriorates in low-light and high-temperature conditions
Solution Approach 1:
The patent performs preliminary measurement of dark current characteristics during a calibration phase, storing local black level values for different pixel clusters. This preliminary action enables the system to compensate for dark current effects during actual image capture without adding real-time processing complexity, improving image fidelity while maintaining operational simplicity.
Solution Approach 2:
The system performs self-calibration by measuring its own dark current characteristics and generating correction parameters automatically. This self-service approach eliminates the need for external calibration equipment or complex real-time correction algorithms, improving image fidelity through simple pre-computed correction values.
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 effectively corrects for dark current non-uniformity, enhancing image accuracy and fidelity in low-light and high-temperature environments by adjusting the global black level value with a local gain correction factor.
Implementation Method 1
The image sensor includes an array of pixels having photosensitive elements (e.g., photodiodes) that absorb a portion of the incident image light and generate image charge upon absorption of the image light
Data Source
AI summary
An imaging system comprises an image pixel array, a dark pixel array, and a controller. The image pixel array includes a plurality of pixel clusters adapted to generate image signals. The dark pixel array is adapted to generate one or more black reference signals corresponding to a global black level value of the imaging system. The controller includes logic that when executed by the controller causes the system to perform operations including determining local black level values for each of the pixel clusters and correcting a first image signal included in the image signals based, at least in part, on the global black level and a first local black level value included in the local black level values.