Solid-State Image Sensor Linearity via Multi-Exposure Segmentation
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Solution Overview
Problem
In image sensors used for illuminance measurement, the linearity of illuminance values is often deteriorated due to saturation in some pixels during long-term accumulation and increased noise from A/D conversion in short-term accumulation values.
Innovation Solution
A solid-state image-capturing element that expands the dynamic range of pixel values based on different exposure times, integrating these values to generate illuminance values, and selectively choosing between short-term and long-term accumulation values based on saturation and noise levels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If long-term accumulation is used to expand dynamic range, then dynamic range is improved, but linearity deteriorates due to saturation in some pixels
Solution Approach 1:
The pixel array is divided into first pixels and second pixels with different accumulation time periods. First pixels accumulate for a longer time to capture low illuminance scenes, while second pixels accumulate for a shorter time to avoid saturation in high illuminance scenes. This segmentation allows the system to maintain linearity across different illuminance levels by selecting appropriate pixel data based on saturation status.
2Adaptability or versatility
If short-term accumulation value is multiplied by gain to expand dynamic range, then dynamic range is improved, but noise increases
Solution Approach 1:
The system uses saturation detection as feedback to determine whether to use long-term or short-term accumulation values. By detecting saturation status in real-time, the system can selectively combine data from different accumulation periods, reducing noise while maintaining expanded dynamic range. The feedback mechanism allows optimal selection between low-noise long-term data and high-dynamic-range short-term data.
3Adaptability or versatility
If multiple exposure times are used for each frame, then dynamic range is expanded, but device complexity increases
Solution Approach 1:
The patent merges the functions of multiple exposure times into a single frame by simultaneously capturing data from first pixels (long-term accumulation) and second pixels (short-term accumulation) within the same frame period. This combining approach expands dynamic range without requiring multiple separate frames, thereby reducing processing complexity while maintaining the benefits of multi-exposure imaging.
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
Improves the linearity of illuminance values by reducing noise and maintaining dynamic range without the need for additional frame memory, enhancing the accuracy of illuminance measurements.
Implementation Method 1
a photodiode that accumulates photoelectric charge
Data Source
AI summary
The present disclosure relates to a solid-state image-capturing element and electronic device capable of improving the linearity of illuminance values. The dynamic-range expander 118 expands dynamic range of a pixel value for each pixel based on the pixel value having different exposure times of a plurality of pixels. The integrator 119 integrates pixel values having the dynamic range expanded by the dynamic-range expander 118 and generates an illuminance value. The present disclosure is applicable to complementary metal-oxide semiconductor (CMOS) image sensor or the like used in, for example, an illuminometer.