CMOS Imaging System Illumination Control for Rolling Shutter Uniformity
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Solution Overview
Problem
In medical endoscope systems, exposure unevenness due to rolling shutter methods in CMOS sensors leads to degradation in image quality, and existing PWM control techniques for illumination struggle to synchronize with exposure cycles effectively.
Innovation Solution
An imaging system with an illumination controller that emits illumination light during the read periods of adjacent horizontal lines in a CMOS sensor, ensuring equal illumination periods for each line, thereby reducing exposure unevenness and expanding the control range of illumination.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If PWM control is used to synchronize illumination with exposure cycle, then exposure unevenness between lines is prevented, but switching speed between lighting and light extinction becomes limited
Solution Approach 1:
The illumination controller starts emitting illumination light before the readout of each horizontal line begins and continues after readout completes, ensuring that all pixels across multiple lines receive equal illumination duration. This preliminary and extended action compensates for the limited switching speed by proactively establishing uniform illumination conditions before line-by-line readout begins.
Solution Approach 2:
The system employs periodic illumination emission synchronized with the rolling shutter readout cycle, where illumination is emitted in regular intervals corresponding to each horizontal line's readout period. This periodic action ensures that despite limited switching speed, each line receives illumination for equal duration, preventing exposure unevenness while working within the constraints of the illumination device's switching capability.
2Productivity
If rolling shutter method is used for readout, then sequential line-by-line reading is achieved, but exposure unevenness between lines occurs
Solution Approach 1:
The illumination controller merges the illumination periods across multiple horizontal lines by emitting light continuously from before the first line's readout begins through after the second line's readout completes. This merging ensures that despite the sequential nature of rolling shutter readout, all lines are exposed to illumination for equal effective duration, combining what would otherwise be disjointed illumination intervals into a unified exposure period.
Solution Approach 2:
Illumination emission begins before the readout of each horizontal line starts, ensuring that when readout commences, illumination is already established and uniform across all lines. This preliminary action compensates for the time delay inherent in sequential line-by-line reading, ensuring that no line is disadvantaged by the rolling shutter method's inherent time progression.
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 prevents exposure unevenness and allows for finer brightness control, independently managing exposure time and illumination emission, thus enhancing image quality in medical endoscope systems.
Implementation Method 1
pixels that receive light and photoelectrically convert the received light to generate an electric signal
Data Source
AI summary
An imaging system includes: an illumination unit that emits illumination light to illuminate a subject; a light receiving unit in which pixels that receive light and photoelectrically convert the received light to generate an electric signal are two-dimensionally arranged; a read unit that sequentially reads the electric signal from the pixels for each horizontal line; and an illumination controller that controls the illumination unit to emit a pulse of the illumination light during a period straddling a read period of the read unit for a first horizontal line and a read period for a second horizontal line which is adjacent to the first horizontal line and which is read immediately after the first horizontal line.