Flicker Detection Circuit for Rolling Shutter Imaging Sensors
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
CMOS imaging sensors with electronic rolling shutters face challenges in detecting flicker caused by fluorescent lighting, especially in non-stationary sequences, due to the spatial variation of illuminance, which is exacerbated by low spatial flicker frequencies in real-time imaging systems.
Innovation Solution
A multi-frame approach that aligns frames to detect misalignment and adjusts exposure time by comparing luminance data from realigned frames to reduce flicker, using motion estimation and compensation circuitry to reposition pixels and generate exposure control information.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a rolling shutter is used in CMOS imaging sensors, then the device complexity is reduced and manufacturing is easier, but spatial flicker is generated under fluorescent lighting
Solution Approach 1:
The patent applies preliminary action by performing frame alignment and flicker detection before final image processing. The system aligns consecutive frames to compensate for rolling shutter effects, then detects flicker patterns in the aligned sequence, enabling proactive correction of illumination artifacts before they manifest as final image defects.
Solution Approach 2:
The patent implements feedback by using the detected flicker signal to adjust exposure timing parameters. The system continuously monitors flicker patterns in real-time and dynamically modifies the exposure schedule to synchronize with the illumination source frequency, thereby eliminating the harmful flicker effect while maintaining the rolling shutter architecture.
2Productivity
If real-time imaging is used to operate at 15 or 30 fps, then productivity is improved, but the spatial flicker frequencies are reduced making detection more challenging
Solution Approach 1:
The patent transitions from analyzing single-frame spatial information to multi-frame temporal-spatial analysis. By examining sequences of aligned frames, the system extracts flicker signals in the temporal dimension while maintaining spatial resolution, thereby detecting low-frequency flicker that would be imperceptible in individual real-time frames.
Solution Approach 2:
The patent performs preliminary frame alignment and temporal signal extraction before flicker detection. This preprocessing step concentrates the flicker signal energy across multiple frames, enhancing its detectability despite the low frequencies present in real-time imaging sequences.
3Measurement precision
If frame alignment is performed to improve flicker detection, then measurement precision is improved, but device complexity increases
Solution Approach 1:
The patent replaces complex mechanical or hardware-based alignment mechanisms with computational image processing methods. The system uses software-based frame registration and temporal signal analysis to achieve precise flicker detection without requiring additional physical components or complex hardware modifications.
Solution Approach 2:
The patent creates temporal copies of the image sequence through frame buffering and digital replication. By working with copied frame data in memory rather than requiring simultaneous physical sensors, the system achieves precise multi-frame analysis without increasing the physical sensor array complexity.
Data Source
Figure 1~2
Figure 3
Figure 4
AI summary
Circuitry, apparatus and methods provide flicker detection and improved image generation for digital cameras that employ image sensors. In one example, circuitry and methods are operative to compare a first captured frame with a second captured frame that may be, for example, sequential and consecutive or non-consecutive if desired, to determine misalignment of scene content between the frames. A realigned second frame is produced by realigning the second frame with the first frame if the frames are determined to be misaligned. Luminance data from the realigned second frame and luminance data from the pixels of the first frame are used to determine if an undesired flicker condition exists. If an undesired flicker condition is detected, exposure time control information is generated for output to the imaging sensor that captured the frame, to reduce flicker. This operation may be done, for example, during a preview mode for a digital camera, or may be performed at any other suitable time.