Phase Difference Autofocus with Pattern Judgment
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Solution Overview
Problem
Existing image forming apparatuses face challenges in accurately focusing due to the effects of specific subject patterns, such as repetitive patterns and high-frequency components, which can lead to false focus detection and errors in phase difference autofocus systems.
Innovation Solution
An image forming apparatus with a plurality of focus detection pixel pairs that detect phase differences and a judging unit to determine if the subject corresponds to a predetermined pattern, allowing for precise focus control by adjusting the focus control based on signals from pixels other than the focus detection pairs, and handling high-frequency subjects by driving the image forming optical system in both front-focused and rear-focused directions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Extent of automation
If phase difference autofocus is used with focus detection pixels, then automatic focusing capability is improved, but false focus detection occurs due to specific subject patterns
Solution Approach 1:
The patent applies preliminary action by detecting subject patterns (repetitive patterns and high-frequency components) before performing phase difference autofocus. The judging unit analyzes the subject image to identify problematic patterns, and only then does the focus detection unit perform phase difference measurement. This prevents false focus detection from occurring in the first place, rather than correcting it afterward.
Solution Approach 2:
The patent introduces a judging unit as an intermediary between the subject image input and the phase difference autofocus execution. This intermediary layer analyzes whether the subject contains problematic patterns (repetitive patterns or high-frequency components) and determines whether phase difference autofocus should be performed. This mediator prevents harmful patterns from directly causing false focus detection.
2Measurement precision
If focus detection pixels are added to the image sensor, then focus detection capability is improved, but device complexity increases
Solution Approach 1:
The patent makes the image sensor pixels universal by enabling them to serve multiple functions. The same pixels are used both for capturing the subject image and for phase difference focus detection. By controlling which pixels are used for focus detection based on subject pattern analysis, the system achieves focus detection capability without adding dedicated focus detection pixels, thus avoiding increased device complexity.
Solution Approach 2:
The patent changes the operational parameters of existing pixels rather than adding new hardware. By dynamically selecting and controlling different pixel groups for different functions (imaging vs. focus detection) based on subject patterns, the system achieves focus detection precision improvement without physical structural changes to the sensor.
3Manufacturing precision
If high-frequency subject components are present, then image detail is improved, but aliasing and moiré issues occur during focus detection
Solution Approach 1:
The patent applies preliminary action by detecting high-frequency components in the subject image before performing phase difference autofocus. The judging unit identifies areas with high-frequency patterns that could cause aliasing or moiré effects, and prevents phase difference measurement in those areas. This preliminary detection and avoidance prevents harmful artifacts from occurring during focus detection.
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 diminishes the impact of specific subject patterns on focus detection, reduces false focus errors, and ensures accurate focusing by adapting focus control based on the detected patterns and spatial frequencies, leading to improved image clarity and reduced aliasing or moiré issues.
Implementation Method 1
an image sensor which has a structure as shown in FIGS. 10A and 10B... a pair of pixels an and bn is placed with respect to a microlens Fn... guides light fluxes from an object... onto the pairs of pixels
Implementation Method 2
a pair of pixels an and bn is placed with respect to a microlens Fn... This structure guides light fluxes from an object, which pass through different areas of a photographing lens, onto the pairs of pixels
Implementation Method 3
The shielding layer 503 has an aperture effect of limiting incident light
Data Source
AI summary
An image forming apparatus includes an image sensor comprising a plurality of pixels at least part of which form a plurality of focus detection pixel pairs, each receiving light rays passing through different pupil areas of an image forming optical system; a detection unit configured to detect a defocus amount, based on a phase difference between signals output from the focus detection pixel pairs in a focusing area; a judging unit configured to determine if a subject corresponds to a predetermined pattern, based on the signals output from the pixels other than the focus detection pixel pairs around the focus detection pixel pairs in the focusing area; and a focus control unit configured to drive the image forming optical system to be in an in-focus state based on the detected defocus amount. The judging unit changes focus control, performed by the focus control unit, based on the determination result.