Rolling Shutter Flicker Compensation via Phase-Offset Image Averaging
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Solution Overview
Problem
Rolling shutter image sensors struggle to capture images under bright flickering light conditions, resulting in alternating dark and light bands due to the flicker effect, which complicates the generation of high dynamic range (HDR) images.
Innovation Solution
A flicker compensation method involving capturing two images with the same or different exposure times, offset by an integer number of flicker periods plus half a flicker period, and averaging or weighting these images to cancel out the flicker effect, which can be implemented in both simple and multiple exposure sensors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If exposure time is shorter than the flicker period to capture bright scenes, then the sensor can handle high brightness situations, but alternating dark and light bands appear in the image
Solution Approach 1:
The patent applies periodic action by capturing multiple images at different phases of the flicker cycle. Specifically, it takes a first image at one phase and a second image offset by half a flicker period, then combines them to cancel out the periodic flicker effect. This transforms the harmful periodic illumination variation into a solvable phase-difference problem that can be resolved through synchronized multi-phase capture and combination.
Solution Approach 2:
The patent changes the temporal parameter of image capture by introducing a specific time offset (half flicker period) between successive image acquisitions. This parameter change allows the sensor to sample the flickering light at opposite phases of its cycle, enabling the combination algorithm to cancel out the flicker effect and produce a uniform image without requiring longer exposure times.
2Illumination intensity
If exposure time is increased to capture low brightness scenes, then more light is captured, but the image integration time exceeds the flicker period causing visual artifacts
Solution Approach 1:
The patent uses periodic action by sampling the scene at multiple distinct phases of the flicker cycle. Even though each individual exposure may be long enough to cover multiple flicker periods, the combination of images taken at different phases (offset by half a flicker period) allows the algorithm to separate and cancel out the periodic flicker component, preserving image quality while enabling longer exposures for low-light conditions.
Solution Approach 2:
The patent applies preliminary action by capturing reference images at different flicker phases before combining them. The first image is captured at one phase and the second image is captured at another phase (offset by half flicker period), preparing the data in advance so that when combined, they pre-correct for the flicker effect that would otherwise manifest as artifacts in the final image.
3Adaptability or versatility
If multiple integrations per frame are used to produce HDR images, then dynamic range is improved, but flicker compensation becomes more complex
Solution Approach 1:
The patent extends periodic action to HDR by applying the same phase-offset sampling strategy across multiple integration intervals. Instead of complicating the flicker compensation for each integration level separately, it uses the consistent half-flicker-period offset approach across all exposure levels, allowing the flicker compensation to be handled uniformly through the HDR combination algorithm without requiring separate complex compensation mechanisms for each integration.
Solution Approach 2:
The patent applies universality by creating a flicker compensation method that works across multiple integration intervals and exposure levels simultaneously. The same time-offset principle applies whether capturing a single-exposure image or multiple exposures for HDR, making the solution universally applicable to both standard imaging and HDR imaging without requiring separate specialized algorithms for each case.
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 method effectively reduces the flicker effect, improving the image dynamic range and minimizing banding artifacts, while maintaining detail in both bright and dark areas of the image.
Implementation Method 1
picture sensor arrays, especially sensors operating on the principle of an electronic rolling shutter
Data Source
AI summary
A flicker compensation method for images taken by an image sensor operating in rolling-shutter mode may include capturing a first image and capturing a second image offset in time from the first image by an integer or zero number of flicker periods, plus half a flicker period. The method may also include producing a compensated image based on an average of the first and second images.