Focus Adjustment Apparatus Steepness Normalization
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Solution Overview
Problem
Existing focus adjustment systems using phase difference detection methods face instability in evaluating defocus amount reliability due to variations in image pickup apparatus settings and subject conditions, leading to inaccurate AF control.
Innovation Solution
A focus adjustment apparatus that includes a signal generating unit, a two-image displacement amount calculating unit, a steepness calculating unit, a steepness normalizing unit, and an evaluating unit to assess the reliability of displacement amounts based on normalized steepness, thereby stabilizing AF control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If reliability of defocus amount is evaluated by using inclination of correlation change amount and similarity level of subject images, then focus adjustment can be performed, but evaluation accuracy deteriorates due to variations in image pickup apparatus settings and subject conditions
Solution Approach 1:
The patent introduces a normalization process that transforms the correlation change amount using a normalization value derived from image signal characteristics (such as standard deviation or mean intensity). This parameter transformation converts absolute correlation values into normalized values that are independent of aperture settings, subject brightness, and contrast conditions, thereby resolving the contradiction between reliable evaluation and measurement precision across varying conditions
Solution Approach 2:
The patent introduces a normalization value as an intermediary parameter that mediates between the raw correlation change amount and the reliability evaluation. This intermediary normalizes the correlation data by dividing by a reference value (such as standard deviation of image signals or mean intensity), creating a standardized metric that can be reliably compared across different shooting conditions without directly altering the original measurement process
2Adaptability or versatility
If aperture value or subject brightness/contrast varies, then different shooting conditions are accommodated, but reliability evaluation becomes unstable
Solution Approach 1:
The patent applies parameter transformation by normalizing the correlation change amount with a normalization value that reflects the actual image signal characteristics under current shooting conditions. This normalization process (e.g., dividing by standard deviation or mean intensity) transforms condition-dependent parameters into condition-independent normalized parameters, enabling stable reliability evaluation across varying aperture values, subject brightness, and contrast levels
Solution Approach 2:
The patent creates an equipotential evaluation framework where all shooting conditions (different apertures, brightness levels, contrast values) are transformed to an equivalent reference state through normalization. By dividing correlation changes by normalization values derived from image signal statistics, the system establishes an equipotential basis for reliability evaluation that eliminates the adverse effects of varying shooting conditions
Data Source
AI summary
A focus adjustment apparatus includes a signal generating unit configured to generate signals of two images respectively corresponding to a pair of light fluxes passing through different pupil regions of a focusing lens, a two-image displacement amount calculation unit configured to calculate a displacement amount of the two images with respect to each other based on a phase difference of the signals of the two images, a steepness calculating unit configured to calculate a steepness of change in a correlation change amount of the two images, a steepness normalization unit that normalizes the steepness, and an evaluating unit configured to evaluate reliability of the displacement amount of the two images based on the normalized steepness.