Electronic Endoscope Strobe Imaging With Multi-Frame Flash Timing
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Solution Overview
Problem
In electronic endoscope systems using a rolling shutter method, the flash exposure period needs to be shorter than the read time of the CMOS image sensor, necessitating high light intensity from the light source, which leads to heat dissipation issues and decreased S/N ratio when gain is increased.
Innovation Solution
An imaging system with a light source unit that emits flashes with a longer period between emissions, allowing for flexible flash exposure times, and an image processing unit that generates display images by combining frames based on flash emission timing, applying gain and spatial filters, and performing interpolation processing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the flash exposure period is set to be shorter than the read time of one line of the CMOS image sensor, then strobe imaging can be performed with the rolling shutter method, but the light intensity of the light source must be increased, causing heat dissipation issues and reduced light source durability
Solution Approach 1:
The patent applies preliminary action by reading and storing pixel signals in the frame buffer before the flash is emitted. Specifically, pixel signals of lines read before strobe light emission are held in advance in a frame buffer as a lower image, and in the next frame, pixel signals of lines above the lower image are directly output. This allows the flash exposure period to be extended beyond the line read time without requiring increased light intensity, as the image data is accumulated over multiple frames rather than captured in a single short exposure.
2Speed
If the flash exposure period is set to be shorter than the read time of one line of the CMOS image sensor, then strobe imaging can be performed, but increasing the gain of the CMOS image sensor causes a decrease in the S/N ratio
Solution Approach 1:
The patent uses preliminary action by accumulating pixel signals in the frame buffer over multiple frames before flash emission. Instead of requiring a short flash exposure that would necessitate high gain amplification, the system pre-reads and stores image data lines in advance, then combines them with subsequent flash-captured lines. This temporal accumulation of signal data improves the S/N ratio without requiring increased gain during the flash exposure period.
3Illumination intensity
If the light intensity of the light source is increased to obtain sufficient brightness for observing vocal cords, then adequate illumination is achieved, but heat dissipation measures must be enhanced and light source durability deteriorates
Solution Approach 1:
The patent applies periodic action by emitting the flash in synchronized periodic intervals with the vocal cord vibration frequency rather than continuously or with extremely short pulses. The flash is emitted at a cycle synchronized with the voice frequency detected by the microphone, with a period from flash end time to next flash start time longer than the flash prohibition period. This periodic timing allows adequate illumination for stroboscopic observation while avoiding excessive heat generation that would compromise light source durability.
4Adaptability or versatility
If the flash exposure period is extended beyond the read time of one line, then the degree of freedom in setting flash exposure period is increased, but the complexity of image processing increases due to need for multi-frame combination
Solution Approach 1:
The patent applies segmentation by dividing the image into distinct segments: an upper image portion captured during the flash exposure period and a lower image portion read in advance and stored in the frame buffer. The image processing unit processes these segmented portions separately and combines them to generate the final display image. This segmentation approach manages processing complexity by handling distinct time-separated data segments rather than requiring complex simultaneous processing of overlapping exposures.
Data Source
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AI summary
According to an aspect of the present invention, provided is an electronic endoscope system including a CMOS image sensor that images an object using a rolling shutter method and a light source device that emits a flash to perform strobe imaging of the object. In the system, the light source device emits a flash such that a period from a flash end time of a certain flash to a flash start time of a next flash is longer than a flash prohibition period during which the emission of the flash is prohibited for at least one frame period. The electronic endoscope system processes a captured image for each frame obtained by the CMOS image sensor on the basis of the emission timing of the flash from the light source device to generate a display image.