Scene-Independent Autofocus via Power Spectrum Ratio
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Solution Overview
Problem
Existing autofocus systems based on spectral signatures are not efficient for all types of scenes, as they rely on scene-specific criteria, leading to inefficiencies in focus error estimation and correction.
Innovation Solution
A method that adjusts a lens by acquiring images at different focus positions, producing power spectra, and calculating a focus error criterion based on the ratio of radial averages of these spectra, independent of scene content, using stored reference criteria to correct focus positions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If spectral signature-based autofocus is used, then focus estimation can be performed, but the system becomes inefficient for certain scene types due to scene-specific criteria dependencies
Solution Approach 1:
The patent transforms the defocus criterion from a scene-dependent spectral signature to a scene-independent parameter by using the ratio of power spectra. This parameter change eliminates variability introduced by different scene contents while maintaining sensitivity to focus errors, thereby improving both productivity and adaptability simultaneously
Solution Approach 2:
The patent introduces an intermediary transformation process that converts raw spectral data into a ratio-based criterion. This intermediary step (computing the ratio of power spectra at different focus positions) acts as a mediator that filters out scene-specific variations while preserving focus-related information, resolving the contradiction between efficiency and adaptability
2Measurement precision
If scene-specific spectral criteria are used for focus estimation, then focus error can be detected, but the measurement precision varies across different scene types
Solution Approach 1:
By changing the measurement parameter from absolute spectral signature to ratio of power spectra, the system achieves consistent measurement precision across all scene types. The ratio operation normalizes the data, making the focus error estimation accurate and universal regardless of scene content
Solution Approach 2:
The patent creates a universal focus estimation criterion that works across all scene types by using the ratio of power spectra. This universal criterion replaces multiple scene-specific criteria, achieving both high measurement precision and broad adaptability simultaneously
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 method provides an objective and scene-independent defocus criterion, allowing for efficient focus error estimation and correction, even under varying conditions, by filtering out noise and focusing on essential spectral components, thereby improving autofocus accuracy.
Implementation Method 1
adjusting a lens (1) comprises adjusting the lens (1) at a first focus position; acquiring a first image of a scene through the lens (1)
Implementation Method 2
producing respective power spectra of the first and second images; and producing a criterion representing the ratio of the power spectra
Data Source
AI summary
A method of adjusting a lens may include adjusting the lens at a first focus position, and acquiring a first image of a scene through the lens. The method may further include adjusting the lens at a second focus position, and acquiring a second image of the same scene through the lens. In addition, the method may include producing respective power spectra of the first and second images, and producing a criterion representing the ratio of the power spectra to estimate a focus error of the lens.