Camera Autofocus Using Face Size Lookup Table
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Solution Overview
Problem
Autofocus systems in digital cameras, such as those using the hill-climb algorithm, are slow in determining focus settings and struggle in low-light environments due to the need for multiple image captures and comparisons, leading to increased time and power consumption.
Innovation Solution
A digital camera with a moveable lens system, image sensor, and processor that uses a pre-populated autofocus table to directly jump to a lens focus position based on detected face size, eliminating the need for a full sweep of lens positions and enhancing focusing speed.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the hill-climb algorithm is used to determine focus settings, then focusing precision is improved, but focusing speed deteriorates
Solution Approach 1:
The patent pre-calculates and stores focus position mappings for different face sizes in a lookup table before operation. During autofocus, the system only needs to detect face size and retrieve the corresponding pre-determined focus position, eliminating the need for time-consuming iterative hill-climb searches while maintaining accurate focusing results.
Solution Approach 2:
The patent creates a simplified model (lookup table) that copies the essential relationship between face size and optimal focus position without replicating the complex iterative optimization process. This table-based representation allows direct retrieval of focus settings based on detected face characteristics, significantly reducing computation time while preserving focusing accuracy.
2Measurement precision
If multiple image captures and comparisons are performed, then focusing accuracy is improved, but time consumption increases
Solution Approach 1:
The system pre-establishes the relationship between face size and optimal focus position through offline calculations and stores it in a lookup table. During actual operation, only face size detection and table lookup are required, eliminating the need for multiple iterative image captures and comparisons while maintaining focusing accuracy.
Solution Approach 2:
The patent extracts the essential parameter (face size) from the complex image analysis task and uses it to directly query pre-computed focus positions. This extraction approach eliminates the need for processing multiple full images through iterative optimization, significantly reducing time consumption while preserving focusing accuracy.
3Measurement precision
If the hill-climb algorithm processes low-frequency and high-frequency components, then focusing precision is improved, but power consumption increases
Solution Approach 1:
The patent performs the computationally intensive frequency analysis and focus optimization calculations in advance, storing only the final focus position mappings in a lookup table. During battery-powered operation, the system only performs simple face size detection and table retrieval, dramatically reducing power consumption while maintaining focusing precision.
4Reliability
If a full sweep of lens positions is performed, then focusing reliability is improved, but productivity deteriorates
Solution Approach 1:
The system pre-determines optimal focus positions for various face sizes and stores them in a lookup table. During video capture or continuous shooting, the system rapidly detects face size and retrieves the corresponding focus position without performing iterative sweeps, maintaining reliable focusing while achieving high frame rates.
Solution Approach 2:
The patent allows the lens to jump directly to the pre-determined focus position based on face size detection, skipping the time-consuming iterative sweep process entirely. This enables rapid focus adjustment that maintains reliability while supporting high-speed continuous capture modes.
Data Source
AI summary
Autofocus operations in a digital camera are described. In one embodiment, a processor detects a face in an image captured by the camera, and calculates the size of the face. It selects from amongst a number of previously stored face sizes, one that is closest to the calculated face size. It retrieves a previously stored lens focus position that is associated with the selected, previously stored face size. It signals a moveable lens system of the digital camera to move to a final focus position given by the retrieved, previously stored lens focus position. Other embodiments are also described and claimed.