CMOS Image Sensor Dynamic Range Extension via Pixel Grouping
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Solution Overview
Problem
CMOS image sensors in mobile applications face limitations in dynamic range extension due to small pixel size, high read noise, and low signal-to-noise ratio, with existing techniques such as multiple integration, logarithmic sensors, dual sensitivity pixels, and spatial-varying sensitivity pixels being inadequate for mobile devices.
Innovation Solution
The solution involves setting different integration times and signal gains for each pixel in a pixel array, with digital data generated for each pixel and interpolated output data created from grouped pixels in the same color plane, allowing for dynamic range extension through a system comprising pixel configuration circuitry, column analog-to-digital converters, and digital processing circuitry.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If multiple integration approach is used to extend dynamic range, then dynamic range is improved, but extra memory is required which increases device complexity
Solution Approach 1:
The pixel array is divided into multiple pixel groups, where each group contains pixels with different integration times. This segmentation allows different regions to capture light for different durations, extending the overall dynamic range without requiring additional memory to store multiple full images.
Solution Approach 2:
Instead of extending dynamic range by adding more memory (one dimension), the patent introduces a temporal dimension by varying integration times across pixel groups. This transforms the problem from a storage capacity issue to a temporal sampling issue, avoiding the need for extra memory.
2Measurement precision
If dual sensitivity pixels approach is used to extend dynamic range, then dynamic range is improved, but extra transistors and storage inside pixel are required which prevents pixel size reduction
Solution Approach 1:
Different pixel groups within the same pixel array are assigned different integration times based on local lighting conditions. This local quality approach allows each region to be optimized for its specific lighting environment without requiring every pixel to have multiple sensitivity levels, thus avoiding the need for extra transistors and storage in each pixel.
Solution Approach 2:
The pixel array serves multiple functions by having different integration times across pixel groups, effectively making the single pixel array perform the role of multiple pixel types (short integration and long integration pixels) without requiring physically different pixel structures.
3Measurement precision
If spatial-varying sensitivity pixels approach is used to extend dynamic range, then dynamic range is improved, but optical masks are required which add cost and limit pixel size
Solution Approach 1:
The patent replaces the mechanical/optical approach of using physical masks with different sensitivities with an electronic control approach. By programmatically setting different integration times for different pixel groups through control circuitry, the system achieves spatial-varying sensitivity without requiring physical masks, thereby reducing manufacturing cost and simplifying the structure.
4Measurement precision
If extra memory is added to store images of different exposures, then dynamic range is improved, but module size increases which is not suitable for mobile devices
Solution Approach 1:
The pixel array is segmented into multiple pixel groups that simultaneously capture light at different integration times. This eliminates the need to store multiple full-resolution images in memory, as the information is captured in parallel during a single exposure event, thereby avoiding the need for large memory capacity and reducing module size.
Solution Approach 2:
The system continuously captures light information across different integration times simultaneously through parallel pixel groups, rather than requiring sequential capture and storage of multiple images. This continuous parallel operation maximizes the use of the pixel array's capturing capability without requiring additional storage space.
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 extends the dynamic range of CMOS image sensors, enabling the capture of high dynamic range images without increasing pixel size or adding extra hardware, maintaining low cost and high performance even in mobile devices.
Implementation Method 1
light is passed through the camera lens to be exposed on an array of pixels having photodiodes such that the captured amount of light in each pixel can be converted into analog electric signals
Data Source
AI summary
A system for processing images may comprise a pixel configuration circuitry enabled to set for each pixel in a pixel array one of a plurality of integration times and one of a plurality of signal gains. A column analog-to-digital converter may be enabled to generate a corresponding digital data for a pixel in the pixel array, and digital processing circuitry may be enabled to interpolate output data from the corresponding digital data for pixels grouped into pixel groups, wherein the pixel group comprises a target pixel and neighboring pixels in a same color plane.