Image Sensor Black Noise Clamping for Long Exposure
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Solution Overview
Problem
Digital image sensors face challenges in maintaining image quality during long exposure periods due to electric noise, optical black noise, and signal clipping, which existing technologies do not effectively address.
Innovation Solution
An image sensor system that uses an electric black reference signal to clamp and adjust the image signal, reducing electric black noise and preventing clipping, while also correcting for optical black noise using shielded pixel values.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If long exposure times are used for imaging under dark light conditions, then the ability to capture dark light conditions is improved, but electric noise and optical black noise significantly degrade image quality
Solution Approach 1:
The patent extracts and separates the black noise component from the image signal by using shielded pixels that only capture optical black noise. This extracted black noise signal is then subtracted from the full pixel signals to remove both optical and electric noise components, thereby improving image quality during long exposure imaging.
Solution Approach 2:
The patent introduces shielded pixels as an intermediary element between the light source and the full pixels. These shielded pixels serve as mediators that capture only the optical black noise component, which is then used as a reference to eliminate noise from the actual image signal through subtraction operations.
2Device complexity
If amplifier circuits are located close to the image sensor, then the device complexity is reduced, but localised heating causes localised noise
Solution Approach 1:
The patent applies local quality by identifying and treating different regions of the image sensor differently. Shielded pixels are strategically placed in specific locations to capture local black noise characteristics, which are then used to correct local noise in adjacent full pixels, addressing the localised heating problem region-by-region.
3Power
If the image signal is amplified to increase signal strength, then the signal-to-noise ratio is improved, but the signal may be clipped by the analogue-to-digital converter
Solution Approach 1:
The patent performs preliminary noise subtraction using the black noise reference signal before the image signal is amplified and converted to digital form. By removing the black noise component in advance, the subsequent amplification operates on a cleaner signal, reducing the risk of clipping while maintaining signal strength and dynamic range.
Data Source
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AI summary
The invention relates to an image sensor system which includes an image sensor (CCD). The image from the image sensor is read out as a video signal. In addition to image values, the video signal also contains electrical and optical black noise. Such noises should be removed from the video signal. A value corresponding to the electrical black noise can be obtained from the image sensor by reading out same additional pixel values which does not originate from image pixels. By subtracting this value from the video signal, a clamped video signal is obtained in which the electrical black noise has been reduced or removed. Additionally, by subtracting the electric block noise value, it is achieved that the clamped video signal is not clipped in the analogue-to-digital converter. The optical black noise may be removed from the signal outputted by the ADC.