Row-Wise Noise Correction Using Black Reference Pixels
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Solution Overview
Problem
CMOS imagers suffer from row-wise noise, which appears as horizontal lines in images due to correlated noise across pixels in a row, and is exacerbated by warm and hot pixels that can disrupt noise correction.
Innovation Solution
Incorporating optically and electrically black reference pixels in each row of the imager's pixel array, which experience the same noise as active pixels, allowing their signals to cancel out row-wise noise without being affected by warm or hot pixel phenomena by effectively removing the photosensor from the noise correction process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If conventional noise correction methods are used, then row-wise noise appears in images, but using reference pixels without removing photosensors introduces warm and hot pixel artifacts
Solution Approach 1:
The patent extracts the photosensor from the reference pixel structure, creating a pixel that contains only the readout circuitry (floating diffusion region, transfer transistor, reset transistor, source follower transistor) without the light-sensitive photosensor component. This extraction eliminates the source of warm and hot pixel artifacts while preserving the ability to measure and correct row-wise noise through the remaining circuit elements that experience the same noise as active pixels.
Solution Approach 2:
The reference pixel serves as an intermediary element that experiences the same row-wise noise as active pixels but without generating warm or hot pixel artifacts. By measuring the signal from this intermediary structure, the system can determine the row-wise noise component and subtract it from active pixel signals, thereby correcting the noise without introducing artifact contamination.
2Measurement precision
If reference pixels include photosensors, then they can measure row-wise noise, but they become susceptible to warm and hot pixel phenomena
Solution Approach 1:
By removing the photosensor from the reference pixel, the patent eliminates the source of unreliable signals (warm and hot pixels) while preserving the readout circuitry that experiences row-wise noise. The floating diffusion region and associated transistors continue to exhibit the same noise characteristics as active pixels, enabling accurate noise measurement without the reliability issues introduced by photosensor-containing reference pixels.
3Object-affected harmful factors
If all pixels in a row are used for noise correction, then noise cancellation is maximized, but warm and hot pixels disrupt the correction accuracy
Solution Approach 1:
The patent segments the pixel population into active imaging pixels and specialized reference pixels. Each row contains both types, with reference pixels dedicated solely to noise measurement and active pixels dedicated to image capture. This segmentation allows the system to use multiple reference pixels per row for noise correction while excluding them from image formation, thereby maximizing noise cancellation capability without allowing warm and hot pixel artifacts to contaminate the correction process.
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
Effectively mitigates row-wise noise in acquired images while preventing adverse effects from warm and hot pixels, ensuring accurate noise correction and image quality.
Implementation Method 1
each one of the cells including a photosensor, for example, a photogate, photoconductor or a photodiode for accumulating photo-generated charge
Data Source
AI summary
An imager having optically and electrically black reference pixels in each row of the imager's pixel array. Since the reference pixels of each row experience the same row-wise noise as active imaging pixels in the associated row, the signals from the reference pixels are used to cancel out row-wise noise from the row of imaging pixels. The reference pixels are designed such that their photosensors are physically or effectively removed from the row-wise noise correction, thus rendering them electrically black or dark. As such, the reference pixels can be used to provide row-wise noise correction without the adverse effects of warm and hot pixels.