Image Sensor Shading Correction for Focus Detection
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Solution Overview
Problem
Existing image capturing systems face challenges in achieving accurate focus detection due to differences in light reception and shading correction between normal pixels and focus detection pixels, leading to decreased image quality and longer calculation times for defocus amounts.
Innovation Solution
An image capturing apparatus and method that utilize separate shading correction data and coefficients for normal pixels and focus detection pixels, allowing for efficient and accurate shading correction and focus detection by distinguishing between different pixel types and applying optimized correction methods.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If separate shading correction data and coefficients are stored for each pixel type (imaging pixels, first focus detection pixels, second focus detection pixels), then focus detection accuracy is improved, but device complexity and memory requirements increase
Solution Approach 1:
The patent divides the image sensor pixels into three distinct types (imaging pixels, first focus detection pixels, second focus detection pixels) and stores separate shading correction data for each type. This segmentation allows each pixel type to be corrected with data optimized for its specific light reception characteristics, thereby improving focus detection accuracy while managing complexity through systematic organization.
Solution Approach 2:
The patent applies the principle of local quality by providing customized shading correction data for each pixel type based on their specific positions and light reception properties. Imaging pixels receive correction data suited for image capture, while focus detection pixels receive correction data optimized for phase difference measurement, ensuring each component receives appropriate correction tailored to its function.
2Manufacturing precision
If separate shading correction data is stored for each pixel type, then image quality is improved, but storage memory capacity requirements increase
Solution Approach 1:
The correction data is segmented by pixel type, with separate storage areas allocated for imaging pixels, first focus detection pixels, and second focus detection pixels. This organized segmentation improves image quality through targeted correction while enabling efficient memory management through structured data organization.
3Measurement precision
If focus detection pixels have openings offset from microlens optical axes to receive pupil-divided light, then focus detection capability is improved, but light reception efficiency decreases
Solution Approach 1:
The patent converts the potential harm of reduced light reception efficiency into a benefit by deliberately offsetting the openings of focus detection pixels from the microlens optical axes. This offset allows the pixels to receive pupil-divided light from different directions, which is essential for phase difference detection. The shading correction data further compensates for the reduced light reception, transforming the disadvantage into an advantage for focus detection capability.
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
Enables high-accuracy focus detection and reduces the time required for calculating defocus amounts by optimizing shading correction for each pixel type, improving image quality and processing efficiency.
Implementation Method 1
an image sensor for collecting via a microlens light incident through an optical system to capture an image
Implementation Method 2
a photoelectric conversion unit group including a plurality of photoelectric conversion units
Data Source
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AI summary
An image capturing apparatus comprises an image sensor compring an imaging pixel for receiving light through an opening with a center position coincident with the optical axis of a microlens, first and second focus detection pixels for receiving pupil-divided light through a first and second opening offset in first and second directions from the optical axis of a microlens, respectively; ROM for storing shading correction data; correction coefficient generation unit for generating shading correction coefficients respectively for the imaging pixel, and the first and second focus detection pixels from the shading correction data; and correction unit for subjecting a signal for the imaging pixel to shading correction with the use of the shading correction coefficient for the imaging pixel, and subjecting signals for the first and second focus detection pixels to shading correction with the use of the shading correction coefficients for the first and second focus detection pixels.