Autofocus Selection Unit Prioritizing High Contrast Frames
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Solution Overview
Problem
Existing autofocus (AF) methods struggle with stability in low luminance or low contrast conditions due to a decreased signal-to-noise ratio when focus detecting points are divided into smaller blocks, leading to scattered focus detecting results.
Innovation Solution
An apparatus that calculates defocus amounts for multiple focus detecting frames and selects one frame for AF control based on the ratio of low contrast frames, prioritizing high contrast frames or switching between different priority areas to ensure reliable AF operations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If focus detecting points are divided into smaller blocks, then measurement precision is improved, but reliability deteriorates due to decreased S/N ratio in low luminance or low contrast states
Solution Approach 1:
The patent dynamically adjusts the focus detecting method based on contrast evaluation. When contrast is high, it uses the divided block method for high precision. When contrast is low, it switches to an undivided method or alternative evaluation to maintain reliability, making the system adaptive to changing conditions rather than fixed
Solution Approach 2:
The patent changes the evaluation parameters (contrast values, S/N ratios) and detection methodology based on the imaging conditions. By monitoring contrast levels and statistical properties of the focus detecting signals, it adjusts which detection method to use, effectively changing system parameters to match environmental conditions
2Manufacturing precision
If focus detecting points are divided into division blocks, then manufacturing precision is improved for detailed focus control, but object-generated harmful factors increase due to noise and scattering in low contrast conditions
Solution Approach 1:
The patent converts the harmful effect of low contrast conditions into a useful diagnostic tool by evaluating contrast metrics and S/N ratios. This evaluation allows the system to detect when divided block detection would be harmful and switch methods accordingly, turning a potential failure mode into a control mechanism
Solution Approach 2:
The system dynamically selects between divided and undivided focus detecting methods based on real-time contrast evaluation. This dynamic adaptation prevents noise and scattering from degrading focus control by switching to a more robust method when conditions are unfavorable
3Measurement precision
If multiple focus detecting frames are used, then measurement precision is improved through statistical evaluation, but device complexity increases
Solution Approach 1:
The patent extracts only the essential information from multiple focus detecting frames - specifically contrast metrics and statistical properties - rather than processing all frame data fully. This extraction approach maintains precision benefits while reducing computational complexity by focusing only on the most relevant features
Data Source
AI summary
An apparatus includes a calculation unit that calculates a plurality of defocus amounts corresponding to a plurality of focus detecting frames obtained by dividing an area corresponding to a display frame, and a selection unit that selects one focus detecting frame which corresponds to one defocus amount used for an AF control. The selection unit changes an AF operation for selecting the one focus detecting frame based on the number of low contrast frames to the number of focus detecting frames or based on reliability selected from part of the area and a ratio of focus detecting frames having a high reliability in the area, or performs an AF operation for selecting the one focus detecting frame so that a high contrast frame is prioritized over a low contrast frame.