Phase Difference Pixels Shorten Exposure for AF Prediction
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Solution Overview
Problem
Conventional focus detection techniques in continuous shooting modes face challenges with slow shutter speeds, leading to increased AF time lag and difficulty in predicting object motion, as they require longer accumulation and reading periods, which hinder the ability to quickly adjust focus and maintain image quality.
Innovation Solution
An image capturing apparatus with phase difference detection pixels performs multiple accumulations with shorter exposure periods than the main image exposure period, allowing for faster focus detection and prediction of the in-focus position based on signals from these accumulations, thereby reducing AF time lag and improving prediction performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If continuous shooting is performed with slower shutter speed to blur background, then sense of dynamism is improved, but AF time lag increases making subject tracking difficult
Solution Approach 1:
The patent segments the image sensor into two distinct functional regions: phase difference detection pixels for focus detection and main image pixels for capturing the final image. This segmentation allows the phase difference detection pixels to perform multiple rapid accumulations independently from the main image exposure, enabling fast AF processing without compromising the quality or timing of the main image capture, thus reducing AF time lag while maintaining continuous shooting speed
Solution Approach 2:
The patent performs preliminary focus detection by accumulating signals from phase difference detection pixels multiple times during the main image exposure period. This preliminary action completes the AF processing before the main image is fully exposed, allowing the system to predict subject position and prepare focus adjustment in advance, thereby reducing AF time lag and improving subject tracking performance
2Measurement precision
If accumulation period is extended to improve focus detection accuracy, then measurement precision is improved, but productivity decreases due to longer processing time
Solution Approach 1:
The patent divides the image sensor into phase difference detection pixels and main image pixels, allowing independent operation. The phase difference detection pixels perform multiple rapid accumulations to achieve high measurement precision for focus detection, while the main image pixels continue capturing images at full continuous shooting speed without being bottlenecked by the longer accumulation process
Solution Approach 2:
The patent performs multiple accumulations of phase difference detection pixel signals during the main image exposure period, using more accumulation cycles than the minimum required for a single focus measurement. This excessive action improves focus detection accuracy and provides data for predicting subject motion, while the process is completed within the existing exposure time frame, maintaining productivity
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 enhances AF prediction performance during continuous shooting by shortening the time required for focus detection and improving the accuracy of in-focus position prediction, allowing for faster and more dynamic subject tracking.
Implementation Method 1
an imaging surface phase difference AF technique in which phase difference detection pixels are arranged in an image sensor, a defocus amount is calculated based on a signal from the phase difference detection pixels
Implementation Method 2
an image sensor having phase difference detection pixels for performing focus detection
Data Source
AI summary
An image capturing apparatus is provided with an image sensor having phase difference detection pixels for performing focus detection, an exposure control unit for causing at least the phase difference detection pixels to perform a plurality of accumulations whose exposure periods are a second exposure period shorter than a first exposure period which is a target for obtaining a main image by the image sensor, and a prediction unit for predicting an in-focus position of a subject based on signals of at least two phase difference detection pixels obtained by at least two accumulations among the plurality of accumulations whose exposure periods are the second exposure period.