Rolling Shutter Image Pickup Light Adjustment for Gradation Reduction
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Solution Overview
Problem
In rolling shutter type image pickup systems, especially in endoscope applications, the simultaneous exposure of all horizontal lines and non-exposure periods lead to light amount changes that cause unwanted gradations in images, which existing techniques attempt to mitigate through global exposure and PWM light adjustments, but these methods have limitations in dynamic range and fringe reduction.
Innovation Solution
An image pickup system and method that control exposure and light adjustment by setting a predetermined exposure period longer than the readout time for all horizontal lines, allowing for simultaneous all-line exposure and non-all-line exposure periods, with a light source capable of adjusting illumination light amounts using current and PWM control, specifically in a first light adjustment mode maintaining a constant level during all-line exposure and adjusting during non-all-line exposure periods.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the exposure period is set to be longer than the readout period of all horizontal lines, then an all-line exposure period can be generated to improve image consistency, but a non-all-line exposure period is also generated which causes light amount changes and image gradations
Solution Approach 1:
The light source is controlled to emit light periodically with different patterns: during the all-line exposure period, the light source emits at a first light amount, and during the non-all-line exposure period, it emits at a second light amount. This periodic light emission control synchronizes with the rolling shutter exposure cycles to ensure consistent illumination across all horizontal lines while preventing gradations caused by light amount changes during readout periods.
Solution Approach 2:
Different light amounts are applied to different time periods: a first light amount is used during the all-line exposure period when all horizontal lines are simultaneously exposed, and a second light amount is used during the non-all-line exposure period when only some lines are exposed. This local differentiation of light quality in the time domain resolves the contradiction by providing appropriate illumination for each exposure scenario.
2Stability of the object's composition
If current light adjustment is used to control the light source, then gentle light amount change can be achieved, but the adjustment speed is limited to about 10 Hz at the highest
Solution Approach 1:
PWM (Pulse Width Modulation) control is employed to periodically switch the light source on and off at high frequency, enabling rapid light amount adjustment that overcomes the speed limitation of current-based gentle adjustment. This periodic switching allows precise control of average light output while maintaining high response speed, suitable for synchronizing with the rolling shutter exposure periods.
3Speed
If PWM driving is used for the light source, then fast light amount adjustment can be achieved, but the minimum pulse width is about several μs which may cause harsh light changes
Solution Approach 1:
The invention applies different light amounts (first light amount and second light amount) to different time periods (all-line exposure period and non-all-line exposure period) rather than using a single uniform light amount. This local differentiation ensures that during the all-line exposure period, sufficient light is provided for proper exposure, while during the non-all-line period, the light amount is adjusted to prevent gradations, thus maintaining overall light amount stability despite using fast PWM switching.
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 enables gentle gradation in images while maintaining a high light amount during all-line exposure and reducing light and dark fringes, allowing for wide dynamic range adjustments and minimizing conspicuous gradations, even at changing speeds of about 10 Hz, with optional correction for more severe gradations.
Implementation Method 1
a plurality of pixels for performing photoelectric conversion are arrayed in a two-dimensional shape in units of horizontal lines
Implementation Method 2
a light source configured to emit illumination light emitted to an object which is a target of image pickup by the image pickup device
Data Source
AI summary
An image pickup system that performs image pickup control of a rolling shutter type such that an all line exposure period and a non-all line exposure period are generated and controls a light source of illumination light to increase or decrease, in a first light adjustment mode, while maintaining a light amount of the illumination light in a first period during the all line exposure period at a predetermined level, a light amount of the illumination light during a second period including the all line exposure period other than the first period and the non-all line exposure period compared with an immediately preceding second period.