Autofocus Lens Position Correction for Rolling Shutter Timing Deviations

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Solution Overview

Problem

When using a rolling shutter system for image sensing, there is a time difference in charge accumulation between different auto focusing areas, leading to lens position deviations during autofocus, resulting in inaccurate focusing.

Innovation Solution

A focus control method that calculates and corrects the in-focus position of the focusing lens based on the read times and positions of image signals from multiple auto focusing areas, ensuring accurate autofocus control by determining the center time and correcting the focusing lens positions.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Speed

If continuous lens movement is used for autofocus, then autofocus speed is improved, but lens position deviation occurs due to charge accumulation time differences

Engineering Contradiction:

Improveautofocus speedVSAvoidlens position accuracy

Core Design Contradiction:

SpeedVSMeasurement precision

Solution Approach 1:

The patent applies preliminary action by recording the lens position at the start time of charge accumulation for each AF area before the actual reading occurs. This allows the system to compensate for lens movement during the charge accumulation period by using the previously recorded position data, thereby maintaining measurement precision while enabling continuous lens movement for faster autofocus.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The patent implements feedback by using the recorded lens position information and read times to calculate and correct the in-focus position. The system continuously monitors lens position during movement and uses this feedback to adjust the final focus determination, ensuring accurate focusing despite continuous lens movement through multiple AF areas.

Inventive Principle:

Principle #23Feedback

2Measurement precision

If multiple AF areas are read at different times, then comprehensive focus evaluation is improved, but lens position consistency deteriorates

Engineering Contradiction:

Improvefocus evaluation accuracyVSAvoidlens position consistency

Core Design Contradiction:

Measurement precisionVSStability of the object's composition

Solution Approach 1:

The patent records the lens position at the start time of charge accumulation for each AF area before reading the image signals. This preliminary recording ensures that even though different AF areas are read at different times, the lens position data corresponds to the correct time point for each area, maintaining position consistency across all areas.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The system uses the recorded lens positions and read times as feedback to calculate the in-focus position for each AF area. By incorporating this temporal and positional feedback, the system maintains lens position consistency across multiple AF areas read at different times, enabling accurate comparative focus evaluation.

Inventive Principle:

Principle #23Feedback

Data Source

PatentUS7945151B2Focus control method and unit determining in-focus lens position based on read times of the autofocus areas and focus lens position and time

Publication Date: 2011.05.17 CANON KK

AI summary

A focus control method is provided that performs focus control by sensing a plurality of images of an object while moving a position of a focusing lens and determining in-focus positions in auto focusing areas located at a plurality of positions. The focus control method calculates an in-focus position of the focusing lens based on the focusing lens position at the time of reading an image signal of each of the auto focusing areas and a degree of focused state of each of the auto focusing area that is based on the image signal of each of the auto focusing areas.