Image Sensor Gain Control for HDR S/N Ratio Improvement
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Solution Overview
Problem
Existing image pickup apparatuses face challenges in achieving a better signal-to-noise ratio (S/N ratio) due to limitations in gain settings for amplifying signals from photoelectric conversion units, particularly in determining optimal gains for outputting video signals without clipping and maintaining high dynamic range.
Innovation Solution
An image pickup apparatus with a processor and memory that controls amplification gains, allowing signals to be amplified with multiple gains, including a first and second gain, where the second gain is smaller, and a controller adjusts the gains to maintain the first gain while changing the second gain for different exposures, enabling the generation of images with improved S/N ratio through HDR image composition.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If the amplifier changes plurality of gains used for amplification in different exposures, then the dynamic range is improved, but the S/N ratio deteriorates due to gain instability
Solution Approach 1:
The patent applies dynamics by making the gain configuration adaptable to different exposure conditions. The amplifier can switch between different gain configurations (first and second gains) depending on the exposure level, allowing the system to optimize for either S/N ratio or dynamic range based on lighting conditions while maintaining overall system stability through controlled transitions between states.
Solution Approach 2:
The patent changes the gain parameter based on exposure conditions. By switching between a first gain configuration (for low light) and a second gain configuration (for bright light), the system optimizes the S/N ratio for each exposure condition. The controller manages these parameter changes to ensure stable operation and prevent S/N ratio deterioration.
2Stability of the object's composition
If multiple column circuits with different gains are used to output video signals, then the dynamic range is expanded, but the device complexity increases
Solution Approach 1:
The patent makes the single amplifier unit universal by enabling it to perform multiple functions through different gain configurations. The same amplifier can operate in a first gain mode for low-light exposures and a second gain mode for bright-light exposures, eliminating the need for separate dedicated amplifiers for each gain level and reducing overall device complexity.
Solution Approach 2:
The patent merges the functionality of multiple column circuits with different gains into a single amplifier unit. By combining the gain-switching capability within one amplifier, the system achieves the dynamic range expansion of multiple circuits while reducing the actual hardware complexity through consolidation.
3Measurement precision
If one gain is set to the lowest gain value to determine input signal level, then the measurement precision is improved, but the S/N ratio worsens for other signal levels
Solution Approach 1:
The patent applies dynamics by transitioning from a static single-gain approach to a dynamic multi-gain approach. The system adapts the gain level based on the input signal characteristics, using the lowest gain for accurate level detection and switching to higher gains when appropriate to maintain S/N ratio, creating a responsive and adaptive measurement system.
Solution Approach 2:
The patent changes the gain parameter based on signal level requirements. By switching between different gain configurations (lowest gain for level detection, higher gains for signal amplification), the system achieves both measurement precision and acceptable S/N ratio across different operating conditions.
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 enhances the S/N ratio of images by maintaining a constant high gain for bright areas and adjusting the gain for dark areas, resulting in improved image quality and noise reduction, even when gain settings are changed by user instruction or automatic control.
Implementation Method 1
a two-dimensionally arranged pixel portion that performs photoelectric conversion
Implementation Method 2
an amplifier that outputs, for each gain, a signal obtained by amplifying a signal based on an output from the photoelectric converters
Data Source
AI summary
An object of the present invention is to obtain an image having a better S/N ratio in accordance with gain settings in an image pickup apparatus that enables amplifying a signal based on output of a photoelectric conversion unit, with a plurality of gains. An image pickup element provided in an image pickup apparatus has a photoelectric conversion unit in which unit pixels are arranged in a matrix and a signal voltage is generating by photoelectric conversion. A column amplifier of the image pickup element can amplify the signal voltage photoelectrically converted with a plurality of gains. An image pickup element control unit performs drive control of the image pickup element to perform gain settings. An image composition unit performs image composition by using a plurality of image signals having different gains. When the image pickup element changes an amplification factor of the column amplifier to output image signals with a plurality of gains, the image pickup element control unit changes a value of a second gain that is smaller than that of a first gain among the gains and performs control so as not to change the value of the first gain.