Dynamic Focus Threshold Adjustment for Noise-Resistant AF
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Solution Overview
Problem
Conventional focus adjustment systems using contrast AF face errors in determining the in-focus position due to noise fluctuations in AF evaluation values, especially under varying conditions such as imaging sensitivity, HPF cut-off frequency, and brightness level, leading to false focus issues.
Innovation Solution
A focus adjustment device and method that utilize an image sensor and a processor to calculate and correct AF evaluation values based on image signals, adjusting the determination threshold values dynamically according to conditions, ensuring accurate focus detection by making the threshold stricter when the evaluation value is below a certain threshold and more lenient when it exceeds it.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single low contrast threshold value is used for focus detection, then the device complexity is reduced, but measurement precision deteriorates due to erroneous determination under varying imaging conditions
Solution Approach 1:
The patent applies dynamics by making the low contrast threshold value variable rather than fixed. The threshold is dynamically adjusted based on imaging sensitivity conditions, allowing the system to adapt to different imaging scenarios (high sensitivity, medium sensitivity, low sensitivity) and prevent erroneous peak detection while maintaining accurate focus detection across varying conditions
Solution Approach 2:
The patent changes the parameter of the threshold value based on imaging sensitivity. By establishing different threshold values for different sensitivity conditions (first threshold for high sensitivity, second threshold for medium sensitivity, third threshold for low sensitivity), the system optimizes measurement precision without excessive complexity
2Illumination intensity
If imaging sensitivity is increased to improve signal quality, then brightness level improves, but noise component increases causing false focus determination
Solution Approach 1:
The patent addresses this contradiction by changing the threshold parameter based on imaging sensitivity. When imaging sensitivity is high (resulting in higher brightness but also higher noise), a first (stricter) threshold is applied. When sensitivity is low (lower brightness but lower noise), a third (more lenient) threshold is applied. This dynamic parameter adjustment resolves the contradiction by adapting the detection criteria to the actual signal-to-noise conditions
3Reliability
If a strict threshold is applied to prevent false focus, then reliability improves, but false negatives increase where valid focus positions are missed
Solution Approach 1:
The patent applies local quality by using different threshold criteria for different imaging sensitivity conditions. Instead of a uniform strict threshold, the system applies: (1) first strict threshold for high sensitivity conditions where noise is problematic, (2) second threshold for medium sensitivity conditions, and (3) third more lenient threshold for low sensitivity conditions where signal strength is the limiting factor. This localized adaptation of threshold quality ensures both reliability and detection success rate are optimized for each condition
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach effectively prevents erroneous focus determination by stabilizing tail portions of the AF evaluation value curve, ensuring the focus lens is accurately moved to the in-focus position even under changing conditions, thereby improving focus accuracy and reducing false focus occurrences.
Implementation Method 1
an image sensor that subjects subject light that has passed through an photographing optical system to photoelectric conversion and outputs an image signal
Data Source
AI summary
A focus adjustment device, comprising a focus detection section that, if, at the time of correction of an evaluation value by a correction section, it is determined that the corrected evaluation value is smaller than a specified threshold value, makes a determination threshold value for detection of a focus position at which the evaluation value exhibits an extreme value, stricter than for a case when it is determined that the corrected evaluation value is greater than the specified threshold value.