Flash Band Compensation in Rolling Shutter Image Pickup Apparatus
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Solution Overview
Problem
Conventional flash band compensation techniques fail to properly detect and compensate for flash bands when multiple external flashes are fired in a single frame, leading to uneven luminance in images captured by rolling shutter image pickup devices.
Innovation Solution
An image pickup apparatus equipped with a detection unit to identify flash bands across consecutive frames and a correction unit that adjusts gains to generate a full-screen flash image, calculating gains based on the light quantity ratio between multiple external flashes to correct regions where flash bands overlap.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional flash band compensation technique is used, then flash band can be compensated when single flash is fired, but the compensation circuit cannot function properly when two or more flashes are fired in one frame
Solution Approach 1:
The patent segments the flash band compensation process into distinct detection and correction stages. The detection unit identifies individual flash bands within a frame, and the correction unit applies specific gain corrections to each detected band, allowing proper handling of multiple flashes that would otherwise overlap and confuse conventional single-stage compensation circuits.
Solution Approach 2:
The patent changes the parameter handling approach by calculating gain based on light quantity ratios between multiple external flashes. Instead of assuming uniform flash conditions, the system adjusts gain parameters dynamically according to the detected flash patterns and their relative intensities, enabling proper compensation even when multiple flashes with different light quantities are fired in one frame.
2Productivity
If rolling shutter image pickup device is used, then sequential exposure and readout can be achieved, but band-shaped flash band appears in image when external flash is fired over shorter period than frame rate
Solution Approach 1:
The patent converts the harmful flash band artifact into beneficial information by using the detected flash band patterns to guide the correction process. The detection unit identifies the precise location and characteristics of flash-induced bands, and this information is then used by the correction unit to apply targeted gain adjustments, transforming the previously harmful luminance differences into a basis for accurate compensation.
Solution Approach 2:
The patent implements a feedback mechanism where the detection unit continuously monitors image signals for flash band patterns, and this detection information feeds back to the correction unit which adjusts gain parameters accordingly. This closed-loop approach ensures that flash bands are dynamically identified and corrected in real-time, preventing the artifact from appearing in the final image while maintaining the efficiency of sequential readout.
3Measurement precision
If flash bands from multiple flashes are detected, then proper detection can be achieved, but complex gain calculation based on light quantity ratio is required
Solution Approach 1:
The patent performs preliminary detection of flash band patterns and light quantity ratios before executing the gain correction process. The detection unit pre-identifies all flash bands within a frame and calculates their relative light quantities in advance, organizing this information in a structured manner that simplifies the subsequent correction step. This preliminary organization of data reduces the computational complexity during the actual correction phase, even though multiple flashes are involved.
Data Source
AI summary
An image pickup apparatus which is capable of properly detecting and compensating for flash bands to generate a corrected image with no different levels of luminance. Based on an image signal output from an image pickup device which sequentially starts exposure and reads out signals for each row of pixels, a flash band appearing in a plurality of frames consecutive in terms of time due to an external flash is detected. Gains are changed with rows of the frames. At least one of the frames in which the flash band was detected is corrected to a full-screen flash image. When flash bands caused by a plurality of external flashes fired in one frame is detected, a gain is calculated based on a light quantity ratio between the external flashes, and a region where the flash bands overlay each other is multiplied by the gain to generate the full-screen flash image.