Pupil-Divided Autofocus Shading Correction for Image Quality
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Solution Overview
Problem
In imaging apparatuses using pupil division for auto focus adjustment, shading corrections are challenging due to variations in light amount across image divisions, affecting image quality if not adequately addressed.
Innovation Solution
The imaging apparatus performs a shading correction process on each pupil division after photographing, utilizing a correction value table to adjust image signals based on factors like image height and lens parameters, ensuring accurate correlation calculations and improved image quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If pupil division process is performed for auto focus adjustment, then focus detection capability is improved, but shading variation across image divisions occurs
Solution Approach 1:
The patent applies local quality by performing shading correction specifically on pupil-divided image data used for focus detection, rather than uniformly processing all image data. The correction is applied locally to the divided image portions where shading variations occur, preserving the focus detection capability while correcting the shading non-uniformity in those specific regions.
Solution Approach 2:
The patent changes the parameter of shading correction by applying it post-photographing to pupil-divided image data. Instead of attempting to correct shading during the pupil division process itself, the system captures the divided image data first, then applies shading correction as a subsequent processing step, thereby adjusting the shading parameter after the fact.
2Manufacturing precision
If shading correction is performed after photographing, then image quality is improved, but correction accuracy is reduced due to unavailable real-time optical parameters
Solution Approach 1:
The patent applies preliminary action by storing correction values in advance in a correction value table during manufacturing or calibration. These pre-calculated correction values account for various optical parameters (F numbers, exit pupil distances) and are saved for later use, enabling accurate post-photographing shading correction without needing real-time optical parameter measurements.
Solution Approach 2:
The patent introduces an intermediary element - the correction value table - that mediates between the pupil-divided image data and the final corrected output. This table stores pre-computed correction factors that bridge the gap between captured image data and properly corrected images, eliminating the need for complex real-time optical parameter analysis.
3Adaptability or versatility
If pupil-divided image data is saved separately as RAW image, then focus adjustment functionality is enhanced, but data processing complexity increases
Solution Approach 1:
The patent merges the pupil-divided image data with normal image data by applying the same shading correction process to both. Instead of maintaining completely separate processing pipelines, the system uses a unified shading correction approach that works on both image types, thereby reducing overall system complexity while preserving the enhanced focus adjustment functionality.
Data Source
AI summary
An imaging apparatus has a focus adjustment mechanism based on auto focus adjustment of an imaging plane phase difference scheme. An imaging element has a plurality of micro-lenses and a plurality of photoelectric conversion units corresponding to the micro-lenses and acquires a pupil-divided image signal. An auto focus (AF) signal processing unit and a camera control unit perform shading correction on a image for each pupil division acquired from the imaging element. The recording medium control unit controls an operation of recording a correction value to be used in shading correction in a recording medium when the image signal before correction for each pupil division is recorded in the recording medium.