Image Sensor Autofocus Exposure Variance Control
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Solution Overview
Problem
Existing image capturing apparatuses face challenges in accurately adjusting the focal point due to variations in exposure times across different areas of the imaging plane, especially when autofocus mode is enabled.
Innovation Solution
An image capturing apparatus that includes an image sensor capable of controlling exposure time for each area of the imaging plane, along with processors and memory to determine exposure times based on luminance information. The apparatus adjusts exposure times so that the variance within the autofocus evaluation frame is minimized when autofocus mode is enabled.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If exposure time is controlled for each area based on luminance information, then image quality is improved, but variance of exposure times across areas increases when autofocus mode is enabled
Solution Approach 1:
The patent applies different exposure time control strategies to different regions: within the autofocus evaluation frame, exposure times are uniform across all areas to ensure accurate contrast evaluation, while outside this frame, exposure times are optimized per-area based on luminance information to maintain image quality. This spatial differentiation resolves the contradiction between focus accuracy and exposure consistency.
Solution Approach 2:
The imaging plane is segmented into the autofocus evaluation frame and other regions. The exposure control system operates differently in each segment: uniform exposure control within the evaluation frame for accurate autofocus, and per-area optimized exposure control outside the frame for image quality, thus resolving the exposure time variance issue while maintaining focus accuracy.
2Measurement precision
If exposure time varies across areas for optimal image quality, then image quality is improved, but contrast evaluation accuracy deteriorates
Solution Approach 1:
Different exposure control policies are applied to different spatial regions: uniform exposure times within the autofocus evaluation frame to ensure accurate contrast evaluation, and area-optimized exposure times outside this frame to maintain image quality. This local differentiation resolves the contradiction between contrast evaluation accuracy and overall image quality.
3Adaptability or versatility
If autofocus mode is enabled with area-based exposure control, then focus adjustment capability is improved, but exposure time inconsistency increases
Solution Approach 1:
The system maintains area-based exposure control for overall image quality while implementing uniform exposure control specifically within the autofocus evaluation frame. This localized uniformity ensures exposure time consistency during autofocus operation, resolving the contradiction between autofocus capability and exposure consistency.
Data Source
AI summary
An image capturing apparatus includes an image sensor that controls an exposure time for each of a plurality of areas and sets an exposure time, based on luminance information for each of the plurality of areas in an image captured by the image sensor, and one or more processors that execute instructions comprising determining whether an autofocus mode for adjusting a focus position of an imaging optical system using a contrast evaluation value within an evaluation frame set for the image is enabled, wherein the exposure time is determined for each of the plurality of areas so that, within the evaluation frame, a variance of exposure times of the plurality of areas in a case where the autofocus mode is enabled is smaller than a variance of exposure times of the plurality of areas in a case where the autofocus mode is disabled.