Solid-State Image Pickup Expanding Dynamic Range via Multi-Sensitivity Pixel Signals
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Solution Overview
Problem
Conventional solid-state image pickup apparatuses face challenges in achieving a wider dynamic range due to limitations in exposure time, leading to information loss and degraded signal-to-noise ratio (S/N) when increasing analog gain, especially in low luminance conditions.
Innovation Solution
A solid-state image pickup apparatus that reads pixel signals from multiple systems with different sensitivities and amplifies them at various rates, synthesizing signals in a later stage to expand the dynamic range without exceeding the input range of analog-to-digital (AD) conversion, thereby maintaining good S/N.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the exposure time is extended to obtain information of low luminance parts, then the sensitivity is improved, but the exposure time cannot be extended beyond a certain limit (e.g., 1/30 second in moving images) due to hand shake or subject blurring
Solution Approach 1:
The pixel array unit is divided into multiple pixel groups, each with different exposure times. This segmentation allows simultaneous capture of signals with different sensitivities, enabling the system to obtain both low luminance information (from longer exposure pixel groups) and high luminance information (from shorter exposure pixel groups) without exceeding the maximum exposure time limit that would cause hand shake or subject blurring.
2Measurement precision
If the analog gain is increased to improve signal amount in low luminance conditions, then the sensitivity is improved, but the bright parts of the screen exceed the input range of AD conversion causing information loss
Solution Approach 1:
Different pixel groups are assigned different exposure times based on their local requirements. Pixel groups capturing low luminance scenes use longer exposure times to accumulate sufficient signal, while pixel groups capturing bright scenes use shorter exposure times to prevent saturation. This local quality differentiation allows the system to optimize signal amount for each region without causing information loss in bright parts.
3Measurement precision
If digital gain is increased to improve signal amount, then the sensitivity is improved, but the gradation becomes coarse
Solution Approach 1:
The system performs analog amplification before AD conversion as a preliminary action to increase signal amount. By amplifying the signal in the analog domain before digitization, the system improves sensitivity without degrading gradation, because the amplification occurs before the quantization process that would otherwise coarseen the gradation.
4Adaptability or versatility
If multiple pixel groups with different exposure times are used to expand dynamic range, then the dynamic range is improved, but the device complexity increases
Solution Approach 1:
Multiple pixel groups with different exposure times are merged into a single pixel array unit structure. The signals from these pixel groups are read out and synthesized in the signal processing system. This merging approach allows the system to expand dynamic range while avoiding the complexity of completely separate imaging systems, as the multiple exposure time paths share common hardware resources.
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 effectively expands the dynamic range and prevents information loss, ensuring high S/N even when increasing analog gain, particularly in low luminance conditions, by varying amplification rates based on sensitivity ratios.
Implementation Method 1
pixels including photoelectric conversion elements
Data Source
AI summary
In a solid-state image pickup apparatus having a pixel array unit composed by two-dimensionally arranging pixels for detecting a physical quantity in a row-column manner, pixel signals of a plurality of systems having different sensitivities are read from the pixel array unit in an analog manner, the pixel signals of the plurality of systems are amplified at respective basis amplification rates when a gain setting of the analog pixel signals is lower than a predetermined gain, and a pixel signal of at least one system having a high sensitivity among the plurality of systems is amplified at a plurality of amplification rates including an amplification rate higher than a basis amplification rate of the system having the high sensitivity when the gain setting is equal to or higher than the predetermined gain.