CMOS Image Sensor Clip Voltage Control for Black Sun Phenomenon
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Solution Overview
Problem
Conventional image pickup apparatuses face challenges in maintaining image quality, particularly in varying shooting conditions, due to the 'black sun phenomenon' caused by high-intensity light, which can lead to fixed pattern noise and poor image visibility, especially in nighttime shooting.
Innovation Solution
An image pickup apparatus equipped with a CMOS image sensor and a correlation double sampling (CDS) circuit that generates a difference image between two exposure conditions, detects black spot areas, and dynamically controls the clip voltage to prevent image quality deterioration by setting an optimal clip voltage based on the detected black spot amount.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a clip circuit is provided to limit the N signal voltage when high-intensity light is incident, then the black sun phenomenon is mitigated, but fixed pattern noise is generated and image quality deteriorates
Solution Approach 1:
The clip voltage is made dynamically adjustable rather than fixed. The voltage controller changes the clip voltage value based on shooting conditions (daytime/nighttime) and detected black spot area, allowing the system to adapt between suppressing black sun phenomenon during daytime and minimizing fixed pattern noise during nighttime.
Solution Approach 2:
The clip voltage parameter is changed according to different operating conditions. The system switches between different clip voltage values (first clip voltage for daytime, second clip voltage for nighttime) and adjusts the degree of clipping based on the detected black spot area, optimizing performance for each scenario.
2Measurement precision
If gain is increased to improve sensitivity for nighttime shooting, then image sensitivity is improved, but fixed pattern noise increases and image quality deteriorates
Solution Approach 1:
The system uses feedback from black spot detection to dynamically adjust the clip voltage. The detector identifies black spots caused by the black sun phenomenon, and this information feeds back to the voltage controller, which then adjusts the clip voltage to an appropriate level that suppresses the black sun phenomenon while minimizing fixed pattern noise generation.
3Measurement precision
If different accumulation times are applied to different pixel groups to detect black sun phenomenon, then black sun detection capability is improved, but manufacturing cost increases and resolution deteriorates
Solution Approach 1:
The invention extracts only the necessary information for black sun detection by analyzing black spot areas in the picked-up images, rather than implementing a complex dual-accumulation-time pixel structure. This approach achieves black sun detection capability while avoiding the increased manufacturing cost and structural complexity of differentiated pixel groups.
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
The solution effectively suppresses the black sun phenomenon while maintaining high image quality across different shooting conditions, preventing fixed pattern noise and ensuring clear images in both daytime and nighttime scenarios.
Implementation Method 1
a photoelectric converter that converts incident light into electric charge
Data Source
AI summary
An image pickup apparatus outputs a picked-up image signal based on a difference between an electric charge signal and a noise signal generated by a photoelectric converter. The apparatus has a generating unit that generates a difference image that is based on a difference between a first image picked up under a first image pickup condition and a second image picked up under a second image pickup condition in which an exposure amount of the photoelectric converter is smaller than the exposure amount of the photo electric converter in the first image pickup condition, a detector that detects a black spot area on the basis of the difference image generated by the generating unit, and a voltage controller that controls a clip voltage that is set to limit a voltage of the noise signal, on the basis of the detected black spot area.