Autofocus System Using Dynamic Mode Switching for Focus Speed
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Solution Overview
Problem
Current autofocus systems in digital image acquisition devices, such as those in mobile phones, suffer from slow and inefficient focus hunting processes, particularly in low-light conditions and when dealing with subjects that do not prioritize focus on specific image regions, leading to blurred images during preview.
Innovation Solution
An autofocus system that utilizes image acquisition parameters like camera and subject motion, ambient light, and lens position to determine sharpness thresholds and adjust focus accordingly, switching between face-detection autofocus and contrast-detection autofocus modes based on performance and stability, with the option to recalibrate and switch to alternative modes if necessary.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If contrast detection autofocus (CDAF) is used to measure focus across image points, then focus coverage is improved, but focus speed deteriorates and low-light performance worsens
Solution Approach 1:
The patent applies local quality by selecting specific regions of interest (such as faces or eyes) within the image to perform autofocus measurements, rather than evaluating the entire image. This localized approach concentrates computational resources on critical areas, improving both focus speed and low-light performance while maintaining adequate focus coverage for the most important subjects.
2Speed
If face detection autofocus (FDAF) is used to prioritize focus on face regions, then focus speed is improved and low-light performance is improved, but focus coverage deteriorates
Solution Approach 1:
The patent implements dynamics by dynamically switching between FDAF and CDAF modes based on scene conditions. When a face is detected, FDAF is used for rapid focusing; when no face is present or for secondary subjects, CDAF provides broader coverage. This dynamic adaptation resolves the contradiction by allowing the system to optimize for speed when possible while maintaining coverage flexibility.
3Measurement precision
If a sweep through multiple points of interest (POI) is performed to determine optimal focus, then focus accuracy is improved, but acquisition time increases
Solution Approach 1:
The patent applies preliminary action by using initial sharpness measurements from a single POI to predict the optimal focus position, thereby avoiding the need to sweep through multiple POI. The system calculates an expected optimal focus position based on the first measurement and directly navigates to that position, significantly reducing acquisition time while maintaining focus accuracy through subsequent verification measurements.
Solution Approach 2:
The patent implements feedback by using the sharpness measurement from the first POI to inform and adjust the focus position for subsequent measurements. The system continuously monitors sharpness values and uses this feedback to refine the focus position, achieving accurate focus without requiring an exhaustive sweep through all POI, thus reducing acquisition time while maintaining precision.
Data Source
AI summary
A method for acquiring an image comprises acquiring a first image frame including a region containing a subject at a first focus position; determining a first sharpness of the subject within the first image frame; identifying an imaged subject size within the first image frame; determining a second focus position based on the imaged subject size; acquiring a second image frame at the second focus position; and determining a second sharpness of the subject within the second image frame. A sharpness threshold is determined as a function of image acquisition parameters for the first and/or second image frame. Responsive to the second sharpness not exceeding the first sharpness and the sharpness threshold, camera motion parameters and/or subject motion parameters for the second image frame are determined before performing a focus sweep to determine an optimal focus position for the subject.