Image Sensor Calibration Using Clear Pixels
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Solution Overview
Problem
The manufacturing of image sensors is hindered by production variations in color filter arrays (CFAs) and IR cutoff filters, leading to inconsistent color responses and requiring special targets and uniform lighting for calibration, which increases costs and slows down the manufacturing process.
Innovation Solution
The use of clear or neutral density pixels, unaffected by CFA production variations, allows for calibration using reasonably uniform surfaces or memory colors, eliminating the need for special targets and uniform lighting, and enabling calibration during routine camera use.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If per module calibration process is performed on RGB image sensors during manufacturing, then color response accuracy is improved, but manufacturing time increases and cost increases due to requiring uniform lighting and special targets
Solution Approach 1:
The image sensor performs self-calibration using its own clear pixels or neutral density pixels as reference, eliminating the need for external calibration equipment. The sensor uses internally available resources (clear pixels that are unaffected by CFA variations) to correct its own color response, thereby avoiding the time-consuming and costly external calibration process while maintaining accuracy.
Solution Approach 2:
The calibration reference function is extracted from the main pixel array by using dedicated clear pixels or neutral density pixels that are physically separated from the color-filtered pixels. These reference pixels are taken out of the CFA structure entirely, allowing them to serve as stable calibration references independent of CFA production variations.
2Measurement precision
If per module calibration process is performed on RGB image sensors during manufacturing, then color response accuracy is improved, but manufacturing cost increases due to requiring uniform lighting and special targets
Solution Approach 1:
The image sensor performs self-calibration using its own clear pixels or neutral density pixels as reference, eliminating the need for external calibration equipment. The sensor uses internally available resources (clear pixels that are unaffected by CFA variations) to correct its own color response, thereby avoiding the time-consuming and costly external calibration process while maintaining accuracy.
Solution Approach 2:
The calibration reference function is extracted from the main pixel array by using dedicated clear pixels or neutral density pixels that are physically separated from the color-filtered pixels. These reference pixels are taken out of the CFA structure entirely, allowing them to serve as stable calibration references independent of CFA production variations.
3Productivity
If clear or neutral density pixels are used for calibration, then calibration process is simplified and manufacturing yield is improved, but device complexity increases due to additional pixel types
Solution Approach 1:
The pixel array is segmented into different functional regions: color-filtered pixels (RGB) for normal imaging and clear pixels or neutral density pixels for calibration references. This segmentation allows each region to serve its specific purpose optimally while the overall structure remains integrated and manageable.
Solution Approach 2:
The clear pixels and neutral density pixels serve multiple functions: they act as calibration references during manufacturing, serve as additional light-sensitive elements for imaging in certain modes, and provide reference data for white balance and color correction algorithms. This multi-functionality justifies their inclusion despite the increased complexity.
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 simplifies the calibration process, reduces costs, and improves the yield of image sensors by compensating for production variations, ensuring consistent color rendering across units.
Implementation Method 1
clear or neutral density pixels, which are free from the types of production variations that affect CFA materials
Data Source
AI summary
Systems and methods are provided for calibrating image sensors. In some embodiments, a processing module of an image system can automatically perform a self-calibration process after a production unit of an image sensor has been integrated into an end product system. For example, the processing module can calibrate a production unit based on one or more reference pixels of the production unit, where the one or more reference pixels have minimal color filtration. In some embodiments, the processing module may perform local calibrations by correcting specifically for spatial variations in a color filter array (“CFA”). In some embodiments, the processing module can perform global calibrations by correcting for optical density variations in the CFA. In some embodiments, a processing module can determine whether the cause of production variations is related to production variations of a CFA or production variations of an infrared (“IR”) cutoff filter.