Dithered Focus Evaluation for Autofocus Shutter Lag Reduction
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Solution Overview
Problem
Current autofocus systems in digital cameras suffer from slow focusing speeds, resulting in shutter lag and a high number of out-of-focus frames during still image and video capture, especially in changing scenes, due to the need for multiple focus adjustments and sensitivity to environmental conditions.
Innovation Solution
Implementing a fast autofocus method that captures autofocus images before and after each frame in a series, evaluating focus quality between these images to make adjustments, using rapid focus systems like piezoelectric motors or liquid lenses to adjust focus settings quickly, and employing a dithered focus evaluation approach to reduce the number of out-of-focus frames by bracketing focus settings around the intended image setting.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If through-the-lens autofocus systems capture multiple autofocus images to determine focus quality, then focus accuracy is improved, but shutter lag increases and focusing speed decreases
Solution Approach 1:
The system performs preliminary focus evaluation by capturing autofocus images at different focus positions before the final image capture. The hill climb method pre-determines the optimal focus position by analyzing contrast values from multiple preliminary autofocus images, allowing the focus lens to be positioned accurately before the actual shot, thereby reducing shutter lag while maintaining focus accuracy.
Solution Approach 2:
The system captures more autofocus images than the minimum single image (typically 5-20 images) to ensure accurate focus determination. This excessive action of capturing multiple images with the focus lens moved to different positions provides redundant data for robust focus evaluation, improving reliability of focus accuracy while the system optimizes the process to manage the time cost.
2Measurement precision
If through-the-lens autofocus systems capture multiple autofocus images for focus evaluation, then focus quality measurement is improved, but the number of out-of-focus frames increases during video capture
Solution Approach 1:
During video capture, the system performs preliminary focus evaluation using a reduced set of autofocus images (e.g., 2-5 images) at different focus positions between video frames. This preliminary evaluation determines whether focus adjustment is needed, allowing the system to maintain focus quality while minimizing the number of out-of-focus frames by making focus decisions more efficiently between video captures.
Solution Approach 2:
The system dynamically adjusts the autofocus evaluation process based on video capture requirements. Instead of using the full still image autofocus sequence, the system adapts by capturing fewer autofocus images during video mode, and uses continuous focus tracking to maintain focus quality across video frames, thereby improving video frame focus rate while preserving measurement precision.
3Speed
If dual lens rangefinder modules are used for fast focus evaluation, then focusing speed is improved, but measurement accuracy decreases due to environmental sensitivity
Solution Approach 1:
The dual lens rangefinder module serves as an intermediary system that provides fast initial focus estimation through triangulation of offset between two lens images. This rangefinder module quickly determines approximate focus distance, which then guides the through-the-lens autofocus system to make precise final focus adjustments, combining the speed of rangefinder with the accuracy of contrast-based evaluation.
Solution Approach 2:
The system replaces the mechanical movement-based dual lens rangefinder measurement with an electronic image processing approach. Instead of relying solely on physical lens separation and triangulation geometry that is sensitive to environmental changes, the system uses digital image correlation and offset calculation from the two lens images, making the measurement more stable against temperature and humidity variations while maintaining fast response.
4Measurement precision
If the focus lens is moved to multiple positions for autofocus evaluation, then focus determination accuracy is improved, but the complexity of the autofocus system increases
Solution Approach 1:
The same image sensor and lens system used for final image capture are also used for autofocus evaluation. The focus lens itself is moved to different positions during autofocus, and the same sensor captures both the autofocus evaluation images and the final image. This multi-functionality eliminates the need for separate autofocus sensors or complex additional optical paths, reducing device complexity while maintaining focus determination accuracy.
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 significantly reduces shutter lag and out-of-focus frames by enabling fast and accurate focus adjustments frame-by-frame, improving focus resolution and stability across varying environmental conditions.
Implementation Method 1
using rapid focus systems like piezoelectric motors or liquid lenses to adjust focus settings quickly
Implementation Method 2
using rapid focus systems like piezoelectric motors or liquid lenses to adjust focus settings quickly
Implementation Method 3
the 5-20 or more autofocus images are analyzed for contrast to determine the focus lens condition that delivers the image with the highest contrast which is deemed the best focus condition
Implementation Method 4
The matched pairs of low resolution images are then analyzed for correlation between the two images to determine the offset between the two images caused by the separation between the two lenses. The offset information is then used along with the lens separation distance to calculate the distance to the scene by triangulation.
Data Source
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AI summary
The invention utilizes an autofocus system (806) that is capable of very fast changes in focus over a relatively small portion of the focus range of the focusing system. When operating continuously in a repeating series of images or frames such as are found in preview mode or in video capture, autofocus images are captured before and after each video frame wherein the autofocus images have different focus settings than the images in the series. The autofocus images are then evaluated for focus quality to determine whether focus adjustments are needed.