Imaging Apparatus Autofocus Control Using Subareas
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Solution Overview
Problem
Conventional autofocus systems in imaging apparatuses face challenges in maintaining focusing accuracy at low illuminance or low contrast, leading to decreased signal-to-noise ratio and potential misfocus on objects other than the main subject.
Innovation Solution
The system sets a main area and multiple subareas around it, acquiring focusing states and in-focus points at various focus lens positions, and performs focusing control using subareas with in-focus points within a predetermined range to improve focusing accuracy when the main area's focusing state does not meet predetermined conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the focus adjustment area is expanded to improve signal-to-noise ratio at low illuminance, then focusing accuracy is improved, but the apparatus may focus on objects other than the main object
Solution Approach 1:
The invention divides the image area into a main focus adjustment area and multiple sub focus adjustment areas. By segmenting the area, the system can selectively use subareas with sufficient focus evaluation values to supplement the main area, improving signal-to-noise ratio without expanding the main area to include unwanted background objects.
Solution Approach 2:
The invention applies different processing strategies to different regions. The main area is processed with standard focus evaluation, while subareas are processed separately and selectively combined only when the main area has insufficient focus evaluation value. This local differentiation allows the system to maintain focus accuracy on the main object while utilizing additional area information when needed.
2Measurement precision
If the focus adjustment area is expanded to improve signal-to-noise ratio, then focusing accuracy is improved, but background objects may enter the focus adjustment area causing misfocus
Solution Approach 1:
The image is segmented into a main focus adjustment area and multiple sub focus adjustment areas. The main area remains defined and controlled, while subareas serve as supplementary sources only when the main area has insufficient focus evaluation values, preventing background objects from contaminating the main focus adjustment area.
Solution Approach 2:
The sub focus adjustment areas act as intermediary sources that provide focus evaluation values only when the main area is insufficient. These subareas serve as a buffer or supplement, allowing the system to maintain focus accuracy without directly expanding the main area to include background objects.
3Reliability
If multiple focus adjustment areas with similar peak positions are selected and averaged to improve reliability at low illuminance, then focusing reliability is improved, but the apparatus cannot cancel randomly generated noises
Solution Approach 1:
The invention evaluates focus evaluation values locally in the main area and selectively in subareas. By comparing focus evaluation values across different regions and selecting only those with sufficient values, the system can improve reliability while maintaining the ability to reject noisy or spurious peak positions through local quality assessment.
Data Source
AI summary
An imaging apparatus sets a main area and a plurality of subareas around the main area in an image obtained from an image sensor, and acquires each focusing state and each in-focus point based on the each focusing state of the main area and the plurality of subareas in an image obtained from the image sensor at each of a plurality of focus lens positions while moving a focus lens. If the focusing state of the main area does not satisfy a predetermined condition, the imaging apparatus performs focusing control using the focusing state of the main area and a focusing state of a subarea having an in-focus point located within a predetermined range from the in-focus point of the main area among the plurality of subareas.