Kalman Filter Black-Level Calibration for CMOS Image Sensors
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Solution Overview
Problem
Conventional black-level calibration technologies for CMOS image sensors fail to accurately account for changes in exposure or gain values, leading to estimation errors and inaccurate image quality, especially in varying light conditions or high-temperature environments.
Innovation Solution
An image-sensing device with a pixel array and control circuit that implements a Kalman filter-based black-level calibration process, using analog-to-digital conversion and computation circuits to generate calibrated digital signals, accounting for exposure and gain value changes by predicting and updating black-level estimates.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional black-level calibration technology is used to smooth jitter over time, then the black-level phenomenon caused by dark current is improved, but the system cannot respond to switching exposure value or gain value, causing estimation error
Solution Approach 1:
The patent implements a dynamic black-level calibration system that adapts to changing exposure and gain values. The control circuit continuously monitors current exposure and gain parameters, and the computation circuit dynamically updates the black-level estimation using a recursive algorithm that incorporates current measurement values and previous estimation results, allowing the system to respond to parameter changes rather than using a static smoothing approach
Solution Approach 2:
The patent employs feedback mechanisms where the control circuit receives current exposure and gain values, compares them with previous values, and uses this feedback information to adjust the black-level calibration process. The computation circuit uses the feedback from current measurements and previous estimations to continuously refine the black-level estimation, ensuring accuracy across varying operating conditions
2Quantity of substance
If dark current is measured from dark pixels in varying light conditions or high-temperature scenes, then more comprehensive calibration data is obtained, but the dark current jitters over time causing inaccurate image brightness
Solution Approach 1:
The system uses feedback from continuous measurements of dark pixel signals to continuously update the black-level estimation. The control circuit receives dark current measurements under varying conditions and feeds them back to the computation circuit, which uses these feedback values to dynamically adjust the calibration, maintaining stability despite environmental variations
Solution Approach 2:
The patent accounts for parameter changes in exposure value and gain value by incorporating these parameters into the black-level calibration algorithm. The computation circuit adjusts the black-level estimation based on current exposure and gain parameters, allowing the system to maintain accurate calibration across different lighting conditions and temperatures
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
The solution effectively stabilizes dark current measurements, improving image quality and consistency across different lighting conditions and temperature environments by accurately calibrating black levels using a Kalman filter-based method.
Implementation Method 1
A photosensitive pixel in a complementary metal-oxide semiconductor (CMOS) image sensor can detect different brightness and wavelengths of light emitted by different objects to obtain corresponding analog signals
Implementation Method 2
due to thermal action of electrons, CMOS image sensors will still generate current even in the absence of light, which can be called dark current
Data Source
AI summary
A method for black-level calibration for an image-sensing device is provided. The image-sensing device includes a pixel array that has a first non-light-sensing region, a second non-light-sensing region, and an image-pixel region. The method includes the following steps: receiving a first analog signal, a second analog signal, and a third analog signal respectively from the first non-light-sensing region, the second non-light-sensing region, and the image-pixel region every predetermined scanning period; utilizing an analog-to-digital converter (ADC) of the image-sensing device to convert the first analog signal, the second analog signal, and the third analog signal to a first digital signal, a second digital signal, and a third digital signal, respectively; and performing a black-level-calibration (BLC) process on the first digital signal, the second digital signal, and the third digital signal to generate a black-level-calibrated digital signal, wherein the BLC process is implemented using a Kalman filter.