Intra-frame Autofocus Scanning for Image Sensors
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Solution Overview
Problem
Traditional inter-frame autofocus methods in image sensors are slow due to the need for multiple frames to compare contrast values, which delays the focusing process.
Innovation Solution
Implementing an intra-frame autofocus system where a subset of lines or pixels within an image frame are scanned at a faster rate multiple times, allowing for contrast or phase value comparison within a single frame to adjust lens movement in real-time.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional inter-frame autofocus method is used, then focus adjustment can be achieved by comparing contrast values, but the focusing process is slow because two image frames must be obtained to make a single comparison
Solution Approach 1:
The image frame is divided into multiple line groups, where specific lines are designated as focus detection lines. By segmenting the frame acquisition process and scanning focus detection lines multiple times within a single frame period, the patent enables contrast comparison without waiting for the next frame, thus reducing focusing time while maintaining measurement precision.
Solution Approach 2:
The patent performs preliminary scanning of focus detection lines multiple times within the current frame before proceeding to scan the remaining lines. This preliminary action allows contrast value comparison to be completed earlier in the frame period, reducing the overall focusing time while maintaining the ability to make accurate contrast comparisons.
2Productivity
If a subset of lines are scanned at a faster rate multiple times, then autofocus speed is improved, but the device complexity increases due to differential scanning rates
Solution Approach 1:
The patent implements dynamic scanning where different line groups are scanned at different rates within the same frame period. The focus detection lines are scanned multiple times at a faster rate, while other lines are scanned at a normal rate. This dynamic approach enables fast autofocus without requiring permanent hardware modifications, achieving high productivity while managing device complexity through software-controlled timing.
Data Source
AI summary
A method of focusing an image sensor includes scanning a first portion of an image frame from an image sensor a first time at a first rate to produce first focus data. A second portion of the image frame from the image sensor is scanned at a second rate to read image data from the second portion. The first rate is greater than the second rate. The first portion of the image frame is scanned a second time at the first rate to produce second focus data. The first focus data and the second focus data are compared, and the focus of a lens is adjusted in response to the comparison of the first focus data and the second focus data.