Adaptive Black Level Compensation for Image Sensor Flickering
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Solution Overview
Problem
The reduction in pixel size and finer fabrication processes in image sensors lead to increased dark current noise, photon shot noise, and MOS device noise, causing screen flickering and slow convergence of black level values, especially in low-intensity illumination environments, which affects device performance and Auto-Exposure speed.
Innovation Solution
An apparatus and method that adaptively calculates a weight for each frame using luminance differences and current frame information to compensate for black level values without increasing the number of black pixels, involving a black pixel average value extraction unit, luminance value extraction unit, black level extraction unit, and black level compensation unit to determine and apply a black level value to valid pixel values.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the number of black pixels is increased to reduce black level value variation, then screen flickering is reduced, but the image sensor size increases
Solution Approach 1:
The patent implements dynamic weighting of black level values from multiple frames based on luminance conditions. The weighting factor is adjusted adaptively: when luminance changes significantly between frames, more recent frames are weighted higher to maintain responsiveness; when luminance is stable, historical frames are weighted more to reduce noise. This dynamic approach achieves stable black level compensation without requiring additional black pixels.
2Reliability
If black level value is obtained by averaging multiple frames, then screen flickering is reduced, but convergence speed decreases
Solution Approach 1:
The patent uses dynamic weighting with a frame-weighting factor that adapts based on luminance changes. When luminance changes significantly (indicating AE adjustment), the weighting factor increases to prioritize current frame black level values, enabling fast convergence. When luminance is stable, the weighting factor decreases to emphasize historical averages, reducing noise and improving stability. This resolves the contradiction between convergence speed and stability.
Solution Approach 2:
The patent changes the weighting parameter dynamically based on luminance conditions. The frame-weighting factor is calculated as a function of luminance change magnitude, allowing the system to transition between emphasizing current frames (fast convergence) and historical frames (noise reduction) based on real-time conditions.
3Power
If analog gain is increased to improve signal in low intensity illumination, then pixel output value increases, but inter-frame deviation and screen flickering increase
Solution Approach 1:
The patent implements feedback by continuously monitoring luminance changes between frames and adjusting the weighting factor accordingly. When analog gain changes cause significant luminance shifts, the system increases the weight of current frame black level values to quickly adapt. This feedback mechanism maintains frame consistency even when analog gain is high by dynamically compensating for the increased noise and deviation.
Data Source
AI summary
An apparatus and method for compensating for a black level in order to solve a screen flickering phenomenon and a problem of convergence speed of a black level value. The apparatus for compensating for a black level includes: a black pixel average value extraction unit averaging black pixel values of a current frame to determine a black pixel average value; a luminance value extraction unit extracting a luminance value from an analog gain and concentration time information of an image sensor; a black level extraction unit calculating a frame weight by using the luminance value and acquiring a black level value of a current frame by using the frame weight, the black pixel average value, and a black level value of a previous frame; and a black level compensation unit compensating for valid pixel values of the current frame by using the black level value of the current frame.