Focus Adjustment Device for Mixed Subject Scenes
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Solution Overview
Problem
The contrast AF method for focus adjustment in imaging devices may incorrectly focus on a subject different from the desired subject in scenes with mixed far and near objects, as it struggles to accurately determine the focus direction in such complex environments.
Innovation Solution
A focus adjustment device and method that sets multiple focus detection regions of varying sizes on an imager, calculates evaluation values from these regions, and uses a control unit to determine the focus direction based on monotonous changes in evaluation values, specifically addressing far-and-near mixing subjects by adjusting the focus lens drive direction and frequency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Extent of automation
If the contrast AF method is used for focus adjustment, then the focus can be adjusted automatically based on image signals, but the focus lens may incorrectly focus on a subject different from the desired subject in scenes with mixed far and near objects
Solution Approach 1:
The imaging region is divided into multiple focus detection regions (first focus detection region and second focus detection region) with different sizes. Each region independently calculates evaluation values to determine focus direction, allowing the system to segment the analysis to avoid confusion between far and near subjects, thereby resolving the contradiction between automated focus adjustment and focus detection accuracy.
2Measurement precision
If multiple focus detection regions are used to improve focus accuracy in mixed subjects, then the focus detection accuracy is improved, but the device complexity increases
Solution Approach 1:
The system segments the imaging region into multiple focus detection regions with different sizes, where each region independently calculates evaluation values. This segmentation approach improves focus detection accuracy by analyzing different spatial zones separately, while the modular structure of independent region processing helps manage system complexity through distributed computation.
Solution Approach 2:
The system performs focus evaluation in multiple focus detection regions rather than a single region. By using at least two regions (first and second focus detection regions) to calculate evaluation values and determine focus direction, the system achieves more accurate focus detection in complex scenes, accepting increased computational effort as a trade-off for improved precision.
3Measurement precision
If the focus lens is driven frequently to determine monotonous changes in evaluation values, then the focus adjustment accuracy is improved, but the time required for focus adjustment increases
Solution Approach 1:
The focus lens is driven a first number of times in a first direction and then driven a second number of times (smaller than the first number) in a second direction opposite to the first direction. This periodic back-and-forth driving pattern allows the system to determine whether evaluation value changes are monotonous, improving focus adjustment accuracy by verifying consistent focus trends while managing adjustment time through controlled drive sequences.
Data Source
AI summary
A direction judgment unit calculates a first evaluation value based on an image signal of a first focus detection region among focus detection regions to judge a drive direction of a focus lens to be in focus and calculates a second evaluation value based on an image signal of at least one second focus detection region smaller than the first region, the focus detection regions being at least partly the same and being different in size. A control unit determines whether a change of the second evaluation value is a monotonous change when the focus lens is slightly driven a first number of times in a first direction judged on the basis of the first evaluation value and the focus lens is slightly driven a second number of times smaller than the first number of times in a second direction opposite to the first direction, and the control unit performs focus adjustment on the basis of the second evaluation value when the change of the second evaluation value is not a monotonous change.