Rolling Shutter Flicker Detection via Fourier Spectrum Analysis
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Solution Overview
Problem
Imaging apparatuses with rolling shutter type image sensors face challenges in detecting flicker caused by periodic light source changes, particularly when imaging timing is fixed, leading to difficulties in distinguishing between flicker-induced and subject-induced stripes, especially during moving-image capturing.
Innovation Solution
The implementation of a flicker detection method using Fourier spectrum analysis on two captured images with different imaging timings, calculating amplitudes and phases, and judging flicker occurrence based on predetermined conditions, including amplitude and phase differences, to differentiate between flicker and subject-induced stripes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If Fourier spectrum analysis is performed on two captured images with different imaging timings, then flicker detection accuracy is improved, but device complexity increases
Solution Approach 1:
The patent segments the image processing task by analyzing two specific captured images with different imaging timings separately, then comparing their Fourier spectrums. This segmentation allows focused computation on flicker detection rather than processing all images, improving accuracy while managing complexity.
Solution Approach 2:
The patent performs preliminary Fourier spectrum analysis on two selected images before making flicker detection judgment. By pre-processing these specific images and comparing their spectrums in advance, the system achieves accurate flicker detection without requiring complex real-time analysis of all captured images.
2Measurement precision
If amplitude and phase conditions are evaluated for Fourier spectrums, then differentiation between flicker and subject-induced stripes is improved, but measurement precision requirements increase
Solution Approach 1:
The patent uses the Fourier spectrum as an intermediary tool that transforms complex image data into frequency-domain representations. By analyzing amplitudes and phases of this intermediate spectrum, the system can differentiate between flicker and subject-induced stripes without directly measuring the difficult-to-detect phase differences in the original images.
Solution Approach 2:
The patent changes the analysis parameters from direct image pixel values to Fourier spectrum amplitudes and phases. This parameter transformation simplifies the differentiation process by converting spatial frequency information into measurable spectral characteristics, making phase measurement more manageable while maintaining differentiation precision.
3Speed
If rolling shutter type image sensor is used, then imaging speed is improved, but flicker detection difficulty increases
Solution Approach 1:
The patent exploits the dynamic nature of the rolling shutter by capturing images at different imaging timings. This dynamic approach allows the system to detect flicker patterns that arise from the interaction between the rolling shutter's sequential scanning and the periodic light source, converting the imaging speed advantage into a detection benefit.
Solution Approach 2:
The patent leverages the periodic action of both the rolling shutter scanning and the flickering light source. By analyzing the Fourier spectrums of images captured at different timings, the system identifies periodic patterns in the brightness variations, enabling flicker detection that utilizes the inherent periodicity of the rolling shutter operation itself.
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 allows for effective flicker detection even under fixed imaging timing conditions, enabling accurate differentiation between flicker and subject-induced stripes, thereby maintaining appropriate exposure and improving image quality during moving-image capturing.
Implementation Method 1
calculates a Fourier spectrum including an amplitude and a phase for each of two captured images acquired by the image sensor of the rolling shutter type and having different imaging timings, by performing Fourier spectrum analysis based on a flicker period serving as a detection target
Data Source
AI summary
An imaging apparatus equipped with a flicker detection function and including an image sensor of a rolling shutter type calculates a Fourier spectrum including an amplitude and a phase for each of two captured images acquired by the image sensor and having different imaging timings by performing Fourier spectrum analysis based on a flicker period serving as a detection target, and judges that flicker with the flicker period serving as the detection target has occurred, when the amplitude of a calculated Fourier spectrum and the phases of the two Fourier spectrums satisfy predetermined conditions and a sum of squares of a pixel value difference between the two captured images for each pixel is larger than a predetermined sum of squares.